Selected FY 2006 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
Nanofluidic transistor.
Imagine a valve to precisely control the flow
of liquids but with dimensions so tiny that only one
molecule at a time can pass through it. Controlled flow of
ions in a liquid was recently demonstrated through very
small nanochannels barely large enough to pass large
molecules. Named “nanofluidic transistors,” the nanochannel
assembly functions in a way similar to ordinary transistors
where the flow of electrons can be regulated by applying a
voltage. Demonstrations were carried out on a 35-nanometer
channel constructed between two silicon dioxide plates; the
channel was filled with water and potassium chloride salt.
The flow of potassium ions could be completely stopped by
applying an electric current across the channel. The
regulation of the flow (or current) of charged molecules was
also demonstrated. This exciting discovery now makes
possible detection and separation of individual molecules in
a fluid. Among the important implications of this discovery
are advanced nanoscale chemical analysis with extreme
sensitivity and the capability of sorting individual
molecules.
Unexpected spontaneous
reversal of magnetization in nanoscaled structures.
New and unexpected magnetic phenomena have
been discovered in ultrathin bilayers of ferromagnetic and
antiferromagnetic films. Ferromagnetic materials (e.g.,
iron) have a positive magnetization due to the alignment of
the magnetic moments. Antiferromagnet materials (e.g.,
nickel oxide) have no net magnetization due to the
anti-parallel alignment of the magnetic moments. In bulk
magnetic materials, regions of aligned magnetic moments,
termed magnetic domains, are expected to align with an
external applied magnetic field. The magnetic strength is
determined by the degree of alignment of the magnetic
domains. In contrast to naturally occurring bulk magnetic
materials, an ultrathin ferromagnetic layer in close contact
with an antiferromagnetic layer will spontaneously align
opposite to the applied magnetic field upon cooling. The
close proximity of the two different layers also results in
an increase in magnetic strength. The ability to control and
detect the magnetic alignment in ultrathin magnetic
materials could lead to new concepts in computer data
storage design. The fundamental understanding of the
unexpected phenomena may also influence future research and
development of magnetic based biological and chemical
sensors.
Nano-electronic
hydrodynamics and turbulence.
Electrons moving across a nanometer-sized
wire have been found to behave hydrodynamically, i.e., like
a liquid flowing from one bucket to another through a small
opening. This behavior is exactly contrary to expectations
from a quantum mechanical prediction, and it has prompted
theoretical predictions of new phenomena. Most striking is
the prediction of possible turbulent electrical transport
with eddy currents in nanoscale conductors that could
seriously limit current flow. Such turbulent currents could
then lead to extremely high electronic temperatures due to
the “friction” of the electrons as they move against each
other, resulting in potential premature failure at much
reduced current flow. Experiments are being carried out to
test these theoretical developments.
Using bioinspired
methods to synthesize and assemble materials.
Biological systems are renowned for
synthesizing inorganic materials under mild conditions and
assembling them into exquisitely shaped structures with high
precision and control. Recently, by emulating the underlying
chemistry and approaches of biology, several inorganic
materials have been synthesized under mild conditions (room
temperature, neutral pH, etc.), with a potential for
significant energy savings in their large-scale manufacture.
Some of the materials synthesized include semiconducting
titanium dioxide, gallium oxide, and zinc oxide for solar
energy conversion; ferroelectric barium titanate
nanoparticles for energy storage; magnetite nanoparticles
for ultra-high density magnetic information storage; and
nanocrystalline palladium for hydrogen storage. Furthermore,
by exploiting the ability of biological macromolecules
(e.g., DNA, proteins, viruses) to self-assemble into large,
well-defined structures and to nucleate the growth of
inorganic materials, researchers have shown that complex
electronic circuit elements and large ordered arrays of
nanoparticles can be assembled with a precision that far
exceeds the current top-down fabrication capabilities.
Unveiling the
superconductor mystery.
Understanding the phenomena of
superconductivity and its mechanism has been among the most
challenging issues facing the condensed matter and materials
physics communities. The mystery of superconductivity is
being tackled by a concerted effort, coupling synthesis and
characterization with theory, modeling, and simulation. The
recent discovery of superconductivity in actinide- and
boron-containing materials indicates superconductivity may
exist in many material systems yet to be discovered. The
search for new materials is augmented by sophisticated
techniques to modify the electronic properties of known
superconducting materials, both chemically and electrically.
Advances in new characterization tools, including proximal
probes, have made possible the discovery of new phenomena,
including competing phases within the superconducting phase.
First principles calculations assisted by generalized
density functional theory enabled accurate predictions of
the electronic structure of superconducting materials. When
coupled to an electron pairing mechanism, numerical models
are being developed to predict the superconducting
transition temperature as a first step towards a priori
design of new superconductors.
Chemical
Sciences, Geosciences, and Energy Biosciences Subprogram
Measuring the
ultrafast motion within a molecule using its own electrons.
Modern ultrafast lasers make it possible, in principle, to
follow in real time the motions of the atoms that comprise a
molecule. However, optical lasers are only indirect probes
of atomic motion. This problem will be alleviated with the
advent of the world’s first x-ray free-electron laser, the
Linac Coherent Light Source (LCLS), since x-rays allow
direct tracking of atomic positions. Until the LCLS is
available, optical laser pulses can be used in clever ways
to track atomic motion in molecules. In one recently
demonstrated example, the molecule’s own electrons are used
as the probe of atomic motion in a highly excited molecule.
The electric field from an intense, optical laser pulse
initially pulls electrons away from the molecule and then
accelerates them back toward it. The highly energetic
electrons scatter from the molecule. Rather than measure the
scattered electrons, as might be done in an electron
diffraction experiment, the new method exploits another
phenomenon that is particularly sensitive to atomic motion.
When the electrons re-collide with the molecule, they emit
x-ray radiation in a process known as high-harmonic
generation (HHG), and it is these x-rays that are detected.
The wavelength of the re-colliding electrons is comparable
to distances between atoms in a molecule; thus, the HHG
x-rays emitted are highly sensitive to atomic motion within
the molecule. This new method shows great promise as a way
of imaging energetic molecules undergoing ultrafast
structural transformations, including the fundamental action
of all of chemistry, and the making and breaking of chemical
bonds.
Sunlight-driven
transformation of carbon dioxide into methanol. The
first step in the chemical transformation of carbon dioxide
into a transportable fuel such as methanol involves the
interaction of light with a catalyst in a process known as
photocatalysis. It has long been known that the
photocatalytic formation of methanol from carbon dioxide can
be initiated by high-energy ultraviolet radiation. Recent
work has demonstrated that the critical first reaction that
splits carbon dioxide into carbon monoxide and a free oxygen
atom can also be triggered with visible light. This advance
makes it feasible to consider harnessing sunlight to drive
the photocatalytic production of methanol from carbon
dioxide. The key to the new advance is to perform the
initial photocatalytic reaction on the walls of the
nanometer-sized channels of a porous silica solid through
the excitation by visible light of a bimetallic catalyst.
The energy from the absorption of light causes an electron
to transfer from one metal in the catalyst to the other and
subsequently activates the gaseous carbon dioxide to
eliminate an oxygen atom to yield the carbon monoxide
product. Various combinations of metals are now being
explored with the goal of designing a complete and
sustainable system to produce methanol.
Catalytic synthesis
of alternative fuels and chemicals. Current
manufacturing technologies for fuels and chemicals are often
inefficient. The need to dramatically improve efficiency in
fuel and chemical production is motivating the search for
new chemical pathways using new catalysts tailored to guide
chemical reactions with precision toward a selected product
without wasteful sub-products. Recent approaches enlist
different catalysts to cooperate in parallel to transform
molecular intermediates. Sometimes referred to as tandem
catalysis, this approach can potentially yield ultrahigh
selectivity. An example is the venerable Fisher-Tropsch
production of diesel fuel from carbon monoxide and hydrogen.
Model catalysts for this polymerization reaction are
typically unselective and yield a mixture of hydrocarbons or
alcohols with carbon-chain lengths varying over a wide
range. For minimum energy consumption and maximum yield, the
ideal process should provide a very narrow carbon-chain
range. Two recent advances may rejuvenate the Fisher-Tropsch
process: the discovery of efficient metathesis catalysts,
which led to the Nobel Prize in Chemistry for 2006, and the
selective activation of carbon-hydrogen bonds. Two catalysts
are necessary to carry out these two very different
functions simultaneously on the same growing polymers. The
carbon-hydrogen activation catalyst limits the yield of
low-end hydrocarbons, and the metathesis polymerization
catalyst simultaneously controls the high-end hydrocarbons.
This can potentially lead to an ideal diesel-oil without the
need for energy-intensive separations. This new tandem
catalysis application is being followed intensely by
researchers worldwide for its potential to revolutionize the
science of alternative fuels and chemicals synthesis.
Carrier
multiplication: a possible revolutionary step toward highly
efficient solar cells. In a normal solar cell, a single
photon from the sun is converted into a single carrier of
electrical current (an electron-hole pair) in a bulk crystal
material called a semiconductor. This process is inherently
inefficient because much of the energy of the solar photon
is wasted as excess heat in the semiconductor. Recent
experiments on the interaction of photons with nanocrystalline samples of semiconductors have demonstrated
a remarkable effect, known as carrier multiplication, in
which a single photon creates multiple charge carriers.
Recent work has demonstrated that as many as seven charge
carriers can be created with a single photon and that the
process is universal, i.e., it occurs in all types of
nanocrystalline semiconductors. These new results suggest
that nanoscale confinement plays an important role in the
carrier multiplication mechanism, which is now thought to be
an instantaneous excitation of multiple electrons by a
single photon. Critical issues must be addressed before an
operational solar cell based on carrier multiplication can
be created, such as separating and harvesting the charge
carriers to create electrical current. However, present
estimates of the conversion efficiency for a solar cell
based on carrier multiplication are as high as 50 percent,
which is about twice that of the best solar cell in current
operation. Doubling solar cell conversion efficiency would
represent a revolutionary advance in our ability to harness
renewable energy from the sun.
Visualizing
chemistry: the promise of advanced chemical imaging. The
emerging possibility of “chemical imaging” is transforming
the way scientists follow the chemical transformation of
molecules on surfaces, within cells, or immersed in other
complex environments. Chemical imaging is the term given to
a set of experimental techniques that use photon beams,
electron beams, or proximal electromechanical probes to
track molecules in two- or three-dimensional space and real
time, while keeping track of chemical identity and even
molecular structure. In the ideal limit, chemical imaging
means nanometer spatial resolution, femtosecond temporal
resolution, and “fingerprint” recognition of the molecular
mass and structure. As a recent example, researchers are
using focused laser beams (space and time information)
coupled with mass spectrometry (chemical identification), to
track specific metabolites in functioning cells.
Multiplexing the mass information allows the simultaneous
mapping of several species. Understanding the metabolic
transformation of important biomolecules in cells is the
first step toward influencing them in service of improved
biochemical processes. Other examples include the use of
chemical imaging to examine single-site catalysts as they
influence reactions on surfaces and light-harvesting
“antenna molecules” that are key participants in
photochemical charge-transfer processes.
Selected FY 2006 Facility Accomplishments
§
The Advanced Light Source (ALS) at LBNL
Experiments begin on new femtosecond X-ray beamline.
Experiments using ultrafast soft x-rays began in FY 2006 on
Beamline 6.0.1.2. High-resolution x-ray spectroscopy and
diffraction at photon energies from 150–1800 eV are now
possible using the new, high-brightness, in-vacuum-undulator
beamline, which increases the flux by a factor of 1000
relative to its predecessor. Beamline 6.0.1, a complementary
hard x-ray beamline using the same insertion device and
extending the photon energy available to users from 2.2–10
keV, was also installed, and its commissioning was begun. In
the first measurements, soft x-ray pulses of 200-femtosecond
duration were used to study phase transitions in vanadium
oxide.
§
The Advanced Photon Source (APS) at ANL
Record nanofocusing with an innovative lens design. A new device, the Multilayer Laue Lens,
developed at Argonne National Laboratory jointly between the
APS and the Center for Nanoscale Materials, has set a
world's record for line size resolution produced with a hard
x-ray beam. The wafer from which the device was made won a
2005 R&D 100 award, given to the world's top 100 scientific
and technological innovations. Enhancements to the device
have now increased its ability to focus the x-rays with an
energy level of 19.5 keV to less than 20 nanometers. Using
the lens, researchers will be able to visualize
three-dimensional electronic circuit boards to find circuit
errors, map impurities in biological or environmental
samples at the nanometer scale, or analyze samples inside
high-pressure or high-temperature cells because hard x-rays,
unlike soft x-rays, are able to penetrate container walls.
This device has potential for a multitude of uses, including
possible incorporation at the nanoprobe beamline at APS
associated with the Center for Nanoscale Materials facility.
§
The National Synchrotron Light Source (NSLS) at BNL
Novel undulator design developed and installed.
A custom-designed, cryogenic-ready, in-vacuum, miniature-gap
hybrid undulator has been installed in the X25 straight
section of the NSLS x-ray ring. The new radiation source,
the first of its kind, will be an order of magnitude
brighter than the original wiggler. By cooling the magnet
array, this insertion device can have a higher magnetic
field and a higher radiation resistance, resulting in a
larger photon energy tuning range. Consequently, unlike
previous miniature-gap undulators in use at the NSLS, this
new undulator will be continuously tunable from 2 to 20 keV
by employing all harmonics up through the 9th. This upgrade
will provide significant benefits to the macromolecular
crystallography program at the NSLS. This technology will be
useful to all medium-energy storage rings in the world.
§
The Stanford Synchrotron Radiation Laboratory (SSRL) at SLAC
Operation at high current of 500 mA.
The SPEAR3 accelerator reached its design current of 500 mA
for the first time during a special run last year. Under
similar test conditions, a selected beam line (BL 6) was
subsequently operated successfully at 500 mA to test the
performance of newly designed optical components, including
the liquid-nitrogen-cooled double crystal monochromator. The
success of this test paves the way for commissioning the
other beam lines. The SPEAR3 accelerator received permission
to operate routinely at 500 mA following an extensive
accelerator readiness review. Authorization for operating
beam lines for users at 500 mA is expected during the
FY 2007 user run, when selected time periods will be
allocated to commission, characterize, and operate beam
lines at high current. SSRL is planning to operate full time
with high current in FY 2008.
§
The Spallation Neutron Source (SNS) at ORNL
Commissioning and initial instrument results. Construction and commissioning of the Spallation Neutron
Source, an accelerator-based neutron source that will
provide the most intense pulsed neutron beams in the world
for scientific research and industrial development, was
completed, and the facility began operations in late
FY 2006. The backscattering spectrometer that is part of the
initial suite of instruments has unprecedented dynamic range
and an energy resolution of better than 3 x 10-6
electron volts. Initial operation of this hardware involved
test measurements of excitations in picoline (a
hydrocarbon), which confirmed the performance of the
instrument.
Selected FY 2005 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
Synchrotron X-Rays Demonstrate Nanoscale Ferroelectricity.
Films only a few atoms thick have been made that retain the
controllable electric polarization needed for next
generation nanoscale devices. Such ultrathin ferroelectric
films have the potential to revolutionize future
electronics, sensors, and actuators. Previous studies
suggested that, as devices are miniaturized, they lose their
ferroelectric character. These studies showed that
ferroelectricity persists in films only 6 atoms thick. This
landmark success was achieved using a unique instrument to
observe thin film growth with high intensity x-rays from the
Advanced Photon Source. X-rays reveal in real time the film
structure as it grows, atomic layer by atomic layer. The
in-situ x-ray techniques developed for this study can now be
used to understand the synthesis and environmental
interactions of other complex materials, thus addressing a
wide range of energy-related challenges.
A Superconductor that Tolerates Magnetic Fields.
One of the biggest obstacles to the practical use of
superconductors is the motion of magnetic flux due to an
electric current in a superconductor. This motion of
magnetic flux reduced the superconducting properties. A
large research effort has gone into finding ways to prevent
energy loss occurring from the movement of magnetic flux in
copper oxide high temperature superconductors. It has been
found that the magnetic flux in certain magnesium diboride
films is intrinsically motionless, or “frozen,” in applied
magnetic fields up to 14 Tesla. Such a complete apathy to an
applied magnetic field has never been seen before in any
other superconductor. While the theoretical explanation for
this behavior has eluded scientists, the experimental
finding has drawn a lot of attention. This behavior may make
it possible to fabricate superconducting wire that can carry
very large electric currents.
Using Electron Spin, not
Electron Charge, to Carry Information. Today’s computers are
based on resistive circuitry using the movement of charged
electrons. The resistance generates heat, and the removal of
this heat is a fundamental limiting factor in creating the
next generation of ultra small and ultra fast circuit
elements. In a remarkable discovery, theorists have
determined that in certain materials a spin current can be
created with the application of a suitably oriented electric
field, with no dissipation of energy. The spin current could
potentially be used to carry out the same logic operations
with no energy loss. This has been verified recently with
experiments on gallium arsenide. This discovery may lead to
computers with much greater capabilities including speed and
capacity due to smaller circuit elements and with a
significant reduction in energy loss.
Plutonium Helps Understand Superconductivity’s Mysteries.
Magnetic resonance studies of the fundamental mechanism
responsible for superconductivity in PuCoGa5
reveal strong similarities to the high-Tc copper
oxide materials. These results confirm earlier theories that
this unique family of plutonium superconductors is nearly
magnetic. This is a new class of superconducting materials
and forms a conceptual bridge between two families of
magnetically mediated superconductors, the heavy fermion
metals and the copper oxides. The discovery of additional
classes of superconducting materials enhances our ability to
understand the mechanisms responsible for high temperature
superconductivity.
Ultrafast Studies of Nanocrystals.
The fastest phase transition between nanocrystal structures
ever recorded has been observed by ultrafast laser
techniques. The reversible structural change in nanocrystals
of vanadium dioxide switches the material from a
semiconductor to a metallic phase, increasing the electrical
conductivity by a factor of 100-10,000 depending on
nanoparticle size. Correspondingly large changes from
optical transparency to high reflectivity occur at the same
time. Lasers with pulses as short as one ten-trillionth of a
second were used to track the phase change in vanadium
dioxide nanoparticles. This discovery may be key to possible
applications requiring extremely rapid switching from
transparent to reflective states. These include protective
overlayers for sensitive infrared detectors, nonlinear
optical switches, fiber-optic pressure sensors, and
electrically or optically triggered transistors that could
switch hundreds of times faster than conventional silicon
devices.
First Direct Observations of Quasiparticles.
Quasiparticles provide a convenient simplification to
describe the behavior of electrons in a superconductor. A
quasiparticle can be thought of as a single particle moving
through a system, surrounded by a cloud of other particles
either pushed away or dragged along by its motion. Prior
investigations of their dynamics have been indirect. Through
the use of a new optical technique it was possible to
perform the first direct study of the dynamics of
quasiparticles in a superconductor. It was discovered that
the quasiparticles can propagate remarkably far, several
hundreds of nanometers. Knowledge of the dynamics of
quasiparticles, specifically their rates of diffusion,
scattering, trapping, and recombination, is critical for the
both the applications and fundamental understanding of
superconductivity.
Confining Electrons in New
Two-dimensional Materials. Transition metal oxides,
like semiconductors, are materials that confine electrons to
a plane. It may now be possible to construct near-perfect
layered materials of two perovskite structured materials. It
has been shown through computational models that a single
layer of LaTiO3 in SrTiO3 will serve
as an electron donor and positive charge layer to retain
those electrons in a thin layer as a two-dimensional
electron gas (2DEG). Electrons behaving like a 2DEG appear
to be an exotic phenomenon, but they are not. Many
semiconductor electronic devices operate by creating just
such a gas by an applied electric field inducing a thin
conducting region at an interface—the field effect
transistor being the prime example. Such thin electron
layers have become a valuable tool for scientists studying
the ways in which electrons organize their collective
behavior. By expanding the materials available to create
2DEGs, new, more diverse opportunities have been created to
expand our knowledge of electronic behavior that in turn can
produce new applications.
Inexpensive Route to Solar Cells Using Nanomaterials.
New and novel semiconductor nanocrystal-polymer solar cells
with surprisingly high efficiencies have been fabricated. In
a solar cell, the conversion of light energy to electrical
current occurs at the nanometer scale. Thus the development
of methods for controlling materials on this scale creates
new opportunities for more advanced solar cells. These
advances are required because, although solar cells based on
silicon and gallium arsenide have achieved high efficiencies
and have found a variety of markets, more widespread
applications remain limited by their high cost of
production. These new cells are formed in an inherently
inexpensive process from a colloidal solution of
semiconductor nanocrystals in a semiconducting polymer. The
unique features of nanosized objects are exploited to
optimize the cell performance by controlling the shape of
the nanocrystals. The performance of the new cells already
rivals that of the best polymer-based devices. While the
power conversion efficiency is still below that of current
amorphous silicon and single crystal devices, there are
opportunities to increase performance further by adding
additional nanocrystal components to capture more of the
solar spectrum. Furthermore, the same methods can be
extended to address other optoelectronic applications, such
as photodetectors and light emitting diodes.
Predicting Magnetism in
Nanomaterials. As recording media and sensors become smaller
and ever-denser, it is increasingly important to control
magnetism in nanostructures. But the physical properties of
magnetic nanostructures are linked in complex ways and are
difficult to predict, much less control. In this work, the
magnetic properties of a cobalt nano-wire next to a platinum
surface step were predicted from first-principles. The
results are in perfect agreement with experiment and show
the importance of a proper quantum mechanical description of
the interplay of different magnetic phenomena. This work,
based on newly developed quantum mechanical models
implemented on high-performance computers, shows that
accurate predictions can be made for a nanostructure
comprised of a few hundred atoms. With continued theoretical
development and more powerful computers, this paves the way
toward prediction and control of more complex and useful
magnetic structures.
Explaining Materials Deformation Mechanisms from
Atomic-scale Measurements.
Using the world's most advanced electron microscope, the
first direct observations of atomic details in complex
crystalline dislocation cores revealed the atomic mechanisms
underlying the deformation of intermetallic compounds with
complex crystal structures. It was discovered that the
diffusion of chromium atoms into and out of the crystal
dislocation cores hinders dislocation motion in Laves-phase
Cr2Hf, a model intermetallic compound, thus
providing a clue as to the origin of the brittleness and
poor low temperature ductility of these intermetallic
alloys. The poor low-temperature ductility of these
intermetallic alloys has prevented their fabrication and use
for decades. Some of the most attractive high-strength
alloys for advanced high-temperature fission and fossil
energy conversion applications possess similar complicated
atomic configurations and lack the low-temperature ductility
required for their fabricated by conventional cold
deformation processes without crack formation. This
discovery provides new atomistic insight into the behavior
of crystal dislocations in complex intermetallic compounds
necessary to design new fabricable alloys with the required
strength at high service temperatures.
Discovery of Mechanism of Surface Mass Transport.
Researchers have discovered that trace concentrations of
sulfur can enhance the rate of mass transport on copper
surfaces by many orders of magnitude and have established
the atomic scale mechanism by which this enhancement occurs.
This discovery was enabled by low-energy electron microscopy
measurements of the motion of singe-atom-high steps on
copper exposed to calibrated doses of sulfur. By comparing
observations of the motion of these steps with theoretical
predictions based on calculations of the electronic
structure of the surface, this research established that
surface mass transport is catalyzed by the formation of a
large number of mobile copper sulfide clusters. Such highly
mobile clusters are believed to be a common feature of
impure surfaces. The enhanced mass transport allows the
formation of much flatter and more defect free surfaces.
This discovery provides insight to many previous puzzling
observations of anomalous surface mass transport. It is an
important advance towards the capability to control the
nanoscale morphology of surfaces, a critical necessity for
nanoscale applications.
Superior Iron-based Alloys and
Steels.
Fundamental laws of alloying
coupled with advanced microanalytical characterization led
to the discovery that yttrium containing iron-based alloys
substantially enhance the stability of the amorphous
(non-crystalline) state. Two technical implications are: (1)
large bulk physical dimensions of this class of amorphous
alloys can be made and (2) this understanding provides a new
direction for designing bulk amorphous metals for structural
and functional applications. Bulk tool steel was fabricated
that was twice as hard as conventional tool steel. These
achievements are milestones in the science of amorphous
metals and the design of functional complex metallic alloys.
Even more important, this research has demonstrated that
microalloying is a new approach for designing bulk amorphous
alloys. Their unique atomic configurations and the absence
of a crystalline lattice allow bulk amorphous metals to
outperform their crystalline counterparts by exhibiting
superior magnetic and mechanical properties and corrosion
resistance coupled with high thermal stability.
Fracture Resistance Mechanism in
Ceramics.
Structural ceramics are complex
structures of micron-sized matrix grains separated by a
nanoscale intergranular film. For many years it has been
observed that certain additives, specifically rare-earth
atoms, influence the ceramic’s fracture resistance. But
detailed information about how this effect is achieved and
how it can be controlled had been inaccessible with current
diagnostic capabilities. Now, new scanning transmission
electron microscopy (STEM) and associated chemical analysis
techniques have revealed the local atomic structure and
bonding characteristics of the grain boundaries with close
to atomic resolution. Applied to silicon nitride ceramics
containing a range of rare-earth additives, these methods
together have revealed how each atom bonds at a specific
location depending on atom radius, electronic configuration
and the presence of oxygen; this variation in bonding sites
can be directly related to the fracture resistance or
toughness of the ceramic.
Better Protective Coatings.
Previously unattainable insight into stress development and
failure mechanisms in thermally grown surface oxides on
metal alloys has been obtained by a new in-situ synchrotron
x-ray technique. This technique enabled, for the first time,
the uncoupling and isolation of mechanical stress
contributions from oxide growth, phase transformations, and
creep deformation processes. For pure thermally-grown
alumina, steady state oxidation creates compressive
stresses. However, when certain “reactive elements” are
added to the alloy, it is found that tensile stresses
develop instead. Maximizing the tensile offset can lead to
dramatic improvement in performance of a protective oxide. A
10 percent shift in the tensile direction can translate to a
40 percent improvement in operating lifetime. Better control
of early stage oxidation leads to thinner, and thus longer
lifetime protective oxides by speeding the transformation to
a stable oxide structure. These results underpin future
alloy development for high-temperature nuclear and fossil
energy generation technologies and more fuel efficient jet
engine applications where operating lifetime has great
economic value.
New Composite Materials that
Respond to Magnetic Fields. Magnetic-field-structured composites are a novel class
of material in which magnetic particles, dispersed in a
polymerizable medium, are organized into chains and other
structures by magnetic fields while the polymer solidifies.
These chains of particles can be electrically conductive,
and this electrical conductivity can be extremely sensitive
to temperature, pressure, and chemical vapors that penetrate
and swell the polymer.
In the present work it was
demonstrated that even modest magnetic fields produced by
simple copper coils cause these materials to contract
significantly, like artificial muscles. This contraction was
found to be accompanied by an enormous, 50,000-fold increase
in electrical conductivity. This is by far the largest
“magnetoresistance” effect ever observed in such modest
magnetic fields and paves the way to using magnetic fields
to control heat and current transport in micro and nano
machines, and to tailoring the sensing response of these
materials.
The “Giant Proximity Effect.”
The reproducible confirmation of the existence of a Giant
Proximity Effect (GPE) has challenged experimentalists for
over a decade. In the traditional Proximity Effect (PE), a
very thin layer of normal metal, when placed between two
thicker superconductor slices, behaves like a
superconductor. That is, superconducting or paired electrons
retain phase coherence even while separated by the normal
metal gap. In the newly discovered GPE, the normal-metal
barrier layer is as much as 100 times thicker than in the PE
case, a result that stands outside of any present theories.
In addition to challenging the theoretical community and
providing new clues to the causes of high-temperature
superconductivity, this result may lead to new advances in
superconducting circuitry as it is relatively easy to
prepare reproducible thick barriers which will improve
device uniformity and yield.
World’s Smallest Nanomotor.
The smallest synthetic motor—a 300 nanometer gold rotor on a
carbon nanotube shaft—has been demonstrated. This
“nanomotor” continues the dramatic advances in the
miniaturization of electromechanical devices and is a key
step in the realization of practical synthetic
nanometer-scale electromechanical systems (NEMS). In initial
testing, the rotor rotated on its nanotube shaft for
thousands of cycles with no apparent wear or degradation in
performance. This is attributed to the unique low-friction
characteristics of the carbon nanotube shaft. The new motor
design has significant potential for NEMS applications. It
should be possible to fabricate arrays of orientationally-ordered
nanotube-based actuators on substrates by using alignment
techniques.
Magnetohydrodynamic Turbulence in Liquid Metals.
Application of a strong magnetic field can completely change
flow characteristics of an electrically conducting fluid.
The transformation may occur in processes ranging from the
generation of sunspots to crystal growth. One particular
aspect of this phenomenon, the damping of flow variations
along the magnetic field lines and the corresponding
development of elongated or even two-dimensional flow
structures, affect nearly all aspects of turbulent flow
behavior, including heat transfer and mixing. In a series of
high resolution numerical experiments it has been shown that
the anisotropy of flow (or directionality of flow) patterns
is a robust universal feature determined primarily by the
strength of the magnetic field, conductivity, and kinetic
energy. Furthermore, the elongation of flow patterns is
approximately the same for flow structures of different
size. This property can be effectively employed for accurate
modeling of magnetohydrodynamic turbulence. The results of
the work are relevant to technological applications, such as
continuous casting of steel, crystal growth, and development
of lithium breeding blankets for fusion reactors.
Nanoparticle
Catalysts.
Methods were developed for depositing and stabilizing
nanometer-sized platinum group metals, including palladium
and rhodium, on surfaces of carbon nanotubes in
supercritical fluid carbon dioxide. Uniformly distributed
monometallic and bimetallic nanoparticles with narrow size
distributions are formed on the surfaces of the carbon
nanotubes. The carbon nanotube-supported palladium and
rhodium nanoparticles demonstrated improved performance over
commercial carbon-based palladium and rhodium catalysts for
hydrogenation of olefins and aromatic compounds. These new
nanoscale catalysts are currently being tested as
electrocatalysts for low temperature polymer electrode fuel
cells applications.
Chemical
Sciences, Geosciences, and Energy Biosciences Subprogram
Timing the
World’s Shortest X-Ray Pulses.
Light sources
based on particle accelerators, such as the Linac Coherent
Light Source (LCLS), will revolutionize x-ray science due to
their unprecedented brightness and extremely short pulse
duration. To take full advantage of x-ray pulses that last
only a few femtoseconds (10-15 seconds), they
must be timed relative to equally short pulses from an
optical laser. Such measurements are vital to a wide range
of LCLS experiments in which a sample is excited by an
optical pulse and probed by an x-ray pulse. At the Stanford
Linear Accelerator Center, ultrashort x-ray pulses were
generated when 80-femtosecond electron pulses from an
accelerator were sent through an undulator magnet; the x-ray
and electron pulses were perfectly coincident in time. A
crystal placed near the path of the electron beam
experienced intense electric fields that altered the optical
properties of the crystal, the electro-optic (EO) effect. An
optical laser beam passing through the crystal sensed the EO
effect, turning the time delay between the optical pulse and
the electron/x-ray pulse into a spatial displacement on a
detector. The current timing resolution of 60 femtoseconds
could be improved to 5 femtoseconds, matching the projected
performance of accelerator-based light sources into the
foreseeable future.
Molecular
Fragmentation Observed in Unprecedented Detail.
Researchers
working at the Advanced Light Source have advanced our
ability to observe the total destruction of a molecule to
new levels of sophistication, challenging theoretical
understanding and paving the way for research to be
performed at next-generation light sources. When a hydrogen
molecule is exposed to x-ray photons of the appropriate
energy, the two electrons it possesses can be ejected at
once, leaving behind two positively charged nuclei that
rapidly explode. Thus, absorption of one x-ray photon causes
the complete destruction of the molecule. Using modern
techniques of three-dimensional imaging and ultrafast
timing, the motions of all four particles from a single
event can be related to one another. The results are
surprising and challenge our current theoretical
understanding of how x-rays interact with matter.
Complete
Ionization of Clusters in Intense VUV Laser Fields.
BES-supported
researchers have developed a theory that explains
recently-observed ionization behavior of xenon clusters that
were exposed to intense, coherent vacuum ultraviolet (VUV)
pulses from a free-electron laser (FEL). Surprisingly, at
intensities that produce only single ionization of an
isolated xenon atom, the clusters irradiated by the FEL
showed massive ionization in which every atom in the cluster
was highly ionized, producing ions with charge states up to
+8. This implies that each xenon atom in the cluster
absorbed about 30 VUV photons. The key difference between
clusters and isolated atoms is that energetic electron-ion
collisions occur within the clusters and modify the
single-photon absorption cross section, thus allowing a
large number of photons to be absorbed. This process is
called “inverse bremsstrahlung” and, when incorporated into
a simple linear absorption model, clearly reproduces the
experimental observations. Theories such as this will be
needed to understand the behavior of matter when it is
exposed to intense, coherent X-ray pulses from
next-generation light sources such as the LCLS.
The
Roaming Atom: Straying from the Lowest-energy Reaction
Pathway.
A fundamental
tenet of modern chemical reaction theory is the concept of
the transition state, a transient molecular entity that lies
on the most direct pathway from reactants to products and
whose properties govern the rate of reaction. Recently, it
was shown that in a simple chemical reaction, the
decomposition of formaldehyde, a substantial fraction of the
dissociating molecules avoid the region of the transition
state entirely. These studies combine ion imaging
experiments with theoretical trajectory calculations to
reveal that the dissociation takes place via a mechanism in
which one hydrogen atom begins to roam away from the
molecule and nearly dissociates, then returns to react with
the remaining hydrogen atom. Along with other recent
findings on reactions such as O + CH3, these
results challenge conventional notions of chemical reactions
and raise the question of how common such processes might
be. A key question is whether such a mechanism applies only
to reactions forming hydrogen, during which a light hydrogen
atom may rapidly explore regions far from the conventional
transition state.
New
Combustion Intermediates Discovered.
A complete mechanism for the combustion of simple
hydrocarbon fuels includes dozens of distinct molecular
species and hundreds of chemical reactions. The
identification of which molecules to include in a combustion
chemistry mechanism still requires experimental detection,
particularly for reactive intermediates. A class of unstable
molecules known as enols, which have OH groups adjacent to
carbon-carbon double bonds, are not currently included in
standard combustion models. In work performed at the
Advanced Light Source, significant quantities of 2, 3, and
4-carbon enols were observed using photoionization mass
spectrometry of flames burning representative compounds from
modern fuels. Concentration profiles of the enols taken in
the model flames demonstrate that their presence cannot be
accounted for by isomerization reactions that convert more
stable molecules into enols. This leads to the conclusion
that an entire class of important reaction intermediates is
absent from current combustion models, and the models will
need substantial revision.
Unified
Molecular Picture of the Surfaces of Aqueous Solutions.
A long-term
controversy exists regarding the detailed, molecular nature
of the surface of an aqueous solution containing molecular
ions (or electrolytes). Joint theoretical and experimental
studies have led to a new, unified view of the structure of
the interface between air and aqueous electrolytes.
Molecular dynamics simulations have shown that in basic salt
solutions positively charged ions (cations) are repelled
from the interface, while negatively charged ions (anions)
exhibit a propensity to migrate toward the surface that
correlates with the anion’s polarizability and physical
size. In acidic solution, however, there is a high
propensity for cations to be located at the air/solution
interface. In this case, both cations and anions are
concentrated at the surface and reduce the surface tension
of water. These conclusions have been verified by
surface-selective nonlinear vibrational spectroscopy
experiments. Understanding the behavior of ions at aqueous
surfaces is important to the heterogeneous chemistry of
seawater aerosols and to the tropospheric ozone destruction
in the Arctic and Antarctic due to reactions on ice pack
covered with sea spray.
Self-Assembled Artificial Photosynthesis.
In natural
photosynthesis, self-assembly of light-absorbing molecules,
or chromophores, at specific distances and orientations is
especially important in two parts of the overall
photosynthetic system: the antenna component, where light is
collected; and the reaction center, where charge is
separated. Recently, a green organic chromophore was
discovered that exhibits photophysical and photoredox
properties similar to those of natural chlorophyll a. When
conjoined with four similar chromophores, the molecules
self-assemble in solution to form an antenna-reaction center
complex. Self-organization of the large structure is
believed due to the propensity of these similar chromophores
to align in a cofacial stacking arrangement. The
self-assembled organic has attributes that closely mimic the
primary events in photosynthesis: efficient light energy
capture over a wide spectral range, energy funneling toward
a core electron-transferring unit, and excited-state
symmetry breaking of a molecular pair resulting in charge
separation. The structure of the new array was determined at
the Advanced Photon Source.
Two-Dimensional Spectroscopy Reveals Energy Transport
Pathways In Photosynthesis.
Photosynthetic antennas capture solar photons and transport
the absorbed energy to the photosynthetic reaction center
where charge separation occurs. Energy transfer by the
antenna is nearly 100 percent efficient, although the
mechanism for the process has been elusive. A novel
spectroscopic technique known as a two-dimensional photon
echo, commonly used in the infrared, has been extended to
the visible spectral region and has revealed important
details about energy transfer in photosynthetic light
harvesting. In antenna pigments from green sulfur bacteria,
distinct energy transport pathways have been identified that
depend on the spatial properties of the pigment-protein
complex. Contrary to the accepted model of a sequential
cascade in energy from high- to low-lying excited states,
these results reveal excited states that are distributed
over two or more chlorophyll molecules and a pathway in
which energy levels are skipped on the way to the lowest
level. The new two-dimensional electronic spectroscopic
method, which measures electronic couplings and maps the
flow of excitation energy, opens the door to investigation
of other photoactive systems and can be applied to improving
the efficiency of molecular solar cells.
How Water
Networks Accommodate an Excess Electron.
In bulk water
an excess electron can become trapped within a cavity formed
by a network of hydrogen-bonded water molecules. This
“solvated electron” is a critical chemical intermediate in
the radiolysis of aqueous solutions. One approach to
understanding the solvated electron is to study the
structure and dynamics of clusters of water containing an
excess electron in the gas phase. This approach has not yet
been successful because these anionic water clusters are
hard to make and because an accurate theoretical description
for them is lacking. Recent work has shown that anionic
clusters containing four to six water molecules can be
created within gas-phase matrices of inert argon clusters,
where their infrared spectra can be obtained. Analysis of
these spectra using density functional theory shows that the
diffuse electron interacts most strongly with a single water
molecule that is hydrogen bonded to two other waters in a
rearranged network. The spectra also exhibit evidence for
the rapid exchange of energy between the vibrations of the
hydrogen atoms on the unique molecule and the excess
electron. This new technique can now be extended to larger
water clusters that better mimic the solvated electron in
bulk water.
Gold, a
Magnificent Nanoscale Catalyst.
When gold
atoms are assembled as tiny clusters smaller than 8
nanometers and attached to the surface of titanium oxide,
they acquire the remarkable ability to dissociate oxygen at
room temperature and insert that oxygen into very specific
locations in molecules. The origin of such unusual
reactivity—discovered some 10 years ago—has until recently
evaded a widely accepted explanation. Numerous parameters in
the material are important and usually cross-correlated:
gold particle dimension and shape, metal oxidation state,
oxide support reducibility, and interaction of the gold with
the support. Separating those parameters in these materials,
which are macroscopically amorphous, would demand special
analytical techniques that are able to focus on the detailed
properties of individual chemical bonds in the solid.
Therefore, researchers pursued a different route using
existing and well-known surface science techniques: they
accurately synthesized and stacked one-atom-thick layers of
gold extended in two dimensions, and supported them on top
of perfect oxide crystals of known structure. They
demonstrated that the nanoscale properties of gold metal are
achievable by controlling the layer thickness to between 2
and 3 atoms. Such knowledge can now be extended to the
manipulation of selective oxidation chemistry or the
discovery and assembly of new catalysts.
Theory
Guides Scientists on How to Extract Hydrogen from Natural
Sources and Store it Efficiently.
Two of the
keys to a hydrogen economy are having an abundant supply of
hydrogen and having materials that can store such hydrogen
in a readily accessible form. Both of those challenges can
be addressed by designing materials—chemical catalysts—that
bind atomic hydrogen with medium strength and release
molecular or gaseous hydrogen with very little heating. A
random or systematic search for such catalysts, even with
high-throughput techniques, would be very expensive and take
many years. Scientists resorted to so-called
density-functional theory, which is an electronic structure
theory of matter, and other theories that describe chemical
reactivity to design the ideal bimetallic catalysts,
combinations of two metals, in special atomic arrangements
that would result in solids with the desired properties.
They arrived at a new theoretical construct called
near-surface alloys of metals, such as a crystal of platinum
containing a single layer of nickel atoms in its second row,
that possesses the unique catalytic behavior sought. Having
by now mapped entire families of such new theoretical
materials—a feat unachievable by direct experimental
means—these scientists have embarked on the challenge of
fabricating these new structures and have already
demonstrated their concept with a few successful examples.
Devising
the Next-Generation Wonder Molecules—Fine Chemistry inside
Nano Cages.
In the future
drugs, fibers, fuel additives, molecular electronics
devices, solar energy conversion dyes, and flavors may be
synthesized in a similar manner using sets of discrete
cavities to contain and isolate single molecules or just
reacting pairs of molecules and catalysts. The
“single-molecule catalysis” concept would allow maximum
control of the environment surrounding a molecule, the
spatial arrangement adopted by its atoms, the type of bonds
made available for reaction, and even how the energy is
coupled to and transferred to the molecule. Such level of
control would result in the ability to break bonds or insert
or remove atoms or change the spatial arrangement of atoms
in very specific ways and not others. The resulting products
would possess properties—chemical, biological, optical,
electronic, or mechanical—superior to those achievable
through less controllable chemistry. Researchers are
beginning to show that this goal may be achievable.
So-called supramolecular or larger-than-molecules cages made
with organometallic compounds were used to host other
organometallic complexes that have catalytic properties,
such as the ability to specifically break carbon-hydrogen
bonds. They have shown that certain carbon-hydrogen bonds
are selectively broken and that only certain members of a
chemical family undergo reaction, and not others. They have
even shown that the constrained environment also leads to
enhanced rate of production of the most desired product,
which is in itself a revolutionary discovery.
Controlling
the Crash-landing of Biomolecules on Surfaces.
Researchers have, for the first time,
demonstrated that peptide ions retain at least one proton
after soft landing on chemically modified, “fluffy”
surfaces. Controlled deposition on surfaces holds great
potential for applications such as selective chemical
separations and analysis. Soft landing refers to the intact
capture of large size-selected, charged molecules on
surfaces of liquids or solids. Previous research suggests
that soft landing provides a means for highly specific
deposition of molecules of any size and complexity on
surfaces using only a tiny fraction of material normally
used in standard synthetic approaches. In the present
studies, peptide ions are attractive as model systems that
can provide important insights on the behavior of
soft-landed macromolecules. The researchers used a specially
designed mass spectrometer configured for studying
interactions of large ions with surfaces. The special
characteristics of the instrument enabled quantitative
investigation of the effect of the speed and mass of ions on
the soft landing process. For example, it was determined
that even collisions with high energies can result in
deposition of intact ions on surfaces.
Removal of
Radium Ions from Water using Special “Grabber” Molecules.
Researchers demonstrated a process that is highly
selective for binding radium cations. It is a significant
challenge to remove radioactive radium cations from
wastewater since the large excess of other non-radioactive
ions in solution can interfere with the selective extraction
of radium. In the new work, a specially designed molecule
was used to selectively bind radium. This supramolecular
assembly made from isoguanosine is just the right size to
extract radium in the presence of other cations such as
magnesium and sodium.
How
Molecules Move through Small Holes.
Measurements of transport through 15-nanometer pores have
been compared to theoretical results to yield new
understanding of differential transport at small scales.
This knowledge is important for an understanding of
separation processes at the molecular level, and could lead
to a new generation of analytical devices based on
microfluidic platforms. By adjusting physical parameters
such as the channel diameter, and applying the appropriate
external electrical potential, arrays of nanochannels—formed
by nanocapillary array membranes—can be made to behave like
digital fluidic switches, and the movement of molecules from
one side of the array to the other side can be controlled.
Combining model calculations with experimental
characterization provides important insights into the
mechanism of molecular transport and, additionally, provides
quantitative measures of the surface characteristics of the
interior of the pores.
Using
Thorium and Uranium to Activate the Carbon-Hydrogen and
Carbon-Nitrogen Bonds in Molecules.
The extent of
electron-sharing in bonds with metals is an important
property in catalysis. The correlation of bond covalency
with reactivity can be elucidated by determining the
reactivity of actinide (thorium, uranium, and other elements
in the same row of the periodic table) ions with multiply
bonded functional groups. Pyridine N-oxide (C5H5N-O),
which has a relatively stable benzene-like ring, can
transfer oxygen atoms to certain transition metals. Chemists
have discovered that some uranium and thorium compounds can
make C-H bonds in pyridine N-oxide more reactive by forming
metal-carbon bonds. The structures of the products produced
in these new reactions have been confirmed by x-ray
crystallography. These reactions provide examples of C-H and
C=N bond activation that is mediated by actinide metals.
These studies may offer insights into catalytic removal of
nitrogen-containing compounds from petroleum feedstocks,
which is necessary to reduce nitrogen oxide emission in
fuels.
Elusive
Carbon Dioxide Binding Mode Discovered in New Uranium
Complex.
Carbon
dioxide (CO2) is a stable molecule with two
strong carbon-oxygen bonds. Inorganic chemists seek to mimic
the catalytic chemical processes by which carbon dioxide is
modified by plants to form sugars. This process can remove
CO2 from the atmosphere and minimize atmospheric
release of CO2 in industrial processes such as
refinement of hydrocarbons. A new exquisitely-designed
uranium complex has been found to react with CO2
such that one electron is transferred from the U3+
center to CO2, producing a species with an
unusual linear CO2 that binds to uranium and has
one weaker oxygen-carbon bond. Uranium is an essential
component of this species because the U3+ ion is
large, electron-rich, and has the right structure to
participate in bonding. This species is unique in that the
CO2 remains linear, with one C-O bond longer and
weaker than the other. The molecular structure, bond lengths
and oxidation state were established experimentally. The
linear M-O-C-O coordination had previously been seen only in
an iron enzyme. The new uranium-CO2 complex
represents a chemical image of a catalytic process and may
make it possible to design new catalysts to reduce the
concentration of CO2 in the atmosphere.
Plutonium
is
Caged and Illuminated by Synchrotron Light.
A new
complexant, which was synthesized to extract plutonium and
other actinide elements selectively, has shown promise to
remove plutonium from mammals. Microscopic crystals (about
the thickness of a human hair) of a plutonium complex have
been produced to provide a structural model in order to
design new actinide-selective binders. Using the Advanced
Light Source, researchers determined the detailed structure
of these crystals and showed that individual plutonium ions
are trapped in cavities produced by eight oxygen atoms from
the binder molecules. This structural determination will
serve as a model of such complexes on which to base the
design of novel molecules that are cages for toxic metals.
Sheer
Energy: Thinner, Cheaper Fuel Cell Catalysts.
Fuel cells
are a major source of clean energy in the hydrogen economy.
Their economic development critically depends on cheaper
electrocatalysts for oxygen reduction. The slow nature of
this reaction causes a major limit in fuel cell efficiency.
High precious metal content is another drawback of existing
technology. Researchers coated five cheaper metals with a
layer of platinum one atom thick and tested them. For most
of the platinum "monolayers," the reaction occurred more
slowly than it does on the thicker platinum layer currently
used in fuel cells. But adding a monolayer of platinum to
the cheaper metal palladium sped up the reaction.
Theoretical computations predicted how the platinum
monolayers are affected by atoms from the underlying layer
of metal. The theory agreed well with the experiments and
showed that a platinum monolayer on palladium balances two
competing needs: it is reactive enough to break the bonds
between oxygen atoms yet does not cling to the oxygen atoms
so tightly that it prevents them from reacting with
hydrogen. This method can dramatically decrease the
expensive metal loading in fuel cells and improve cost and
performance.
Advances
in Computational Chemistry Research.
Basic research in computational chemistry has resulted in
a superior method for the prediction of chemical behavior
from computational quantum mechanics and statistical
mechanics. The method is based on treating the solvent in
which a molecule is placed as a continuum, and determining
the cavity-formation energy from statistical mechanics, and
the electric contributions from quantum mechanics. This work
has now been published and a leading chemical process
simulation company has incorporated this method into the
most recent release of their industry dominating process
simulator. This work will impact modern industrial plant and
process design and lead to higher energy efficiencies
through effective modeling of manufacturing processes.
Is CO2
Gone When You Put It In The Ground?
There are
only two options for dealing with increasing CO2
concentrations in the atmosphere—get rid of new CO2
actively or discontinue producing it and wait for natural
processes to remove the excess over a very long time. Both
approaches will likely be needed in the future. Researchers
have been developing capabilities for realistic modeling of
CO2 injection into deep geological formations and
for understanding dynamic processes associated with the
injection in order to provide a scientific basis for
evaluating the injections feasibility. Computational models
were developed for coupling fluid properties, chemical and
thermodynamic data, and rock-fluid interaction measurements.
Reservoir dynamics were investigated on different levels of
complexity and scale for natural and engineered systems.
These types of calculations also form the basis for
understanding possible leaks which may be major regulatory
and insurance concerns for large scale geological CO2
sequestration. The improved computational codes from this
project were also used as the basis for design calculations
for CO2 injection at the Frio Test Site as part
of the Office of Fossil Energy funded Climate Change
Technology Program.
Improving
Our Vision of the Subsurface.
Large scale
subsurface seismic measurements, although adequate for
simple oil and gas exploration or waste site
characterization, are inadequate for high hydrocarbon
recovery rates or more effective environmental remediation
or monitoring. Research is providing a better understanding
of geophysical measurements of compressional and shear wave
velocities, elastic moduli, and seismic anisotropy as they
vary as functions of porosity, permeability, fluid contents,
and stresses. A fiber-optic “optical” strainmeter has been
developed that provides spatially averaged properties over a
centimeter or “core” length scale intermediate between point
measurements and a meter-scale bulk-measurements. The
increased accuracy and sensitivity in measuring elastic
deformation during applied sinusoidal stress will enable
better discrimination between strain (elastic wave
transmission efficiency) and phase lags (attenuation
indicative of fluid content and type). In addition, the
highly precise optical strain gage measurements will allow
higher resolution testing of the significance of different
types of heterogeneity at the core scale, in order to enable
prediction of these properties at larger scales. The fiber
optic sensor has been demonstrated to have a significantly
higher sensitivity than other strain gages.
The Auxin
Receptor: A Holy Grail in Plant Science.
The plant
growth hormone called auxin is a small molecule, indole
acetic acid (IAA)—too small to have the expected breadth of
“informational” content to achieve its myriad effects of
controlling the growth of leaves, stems, roots, flowers,
fruits, and growth changes in response to light and gravity.
Recent research demonstrated that IAA interacts directly
with a much larger molecule, a protein, which was earlier
shown to affect plant growth by stimulating the expression
(activation) of certain growth-related genes. Now the
solution to the mystery of auxin action is becoming clear.
It turns out to be similar to an electric switch, but a bit
more complex. We are beginning to unravel the molecular
details of auxin’s biological activity.
Selected FY 2005 Facility Accomplishments
§
The Advanced Light Source (ALS)
Beam-Size Stability Improved.
Over the last five years, elliptically polarizing undulators
(EPUs) have been used very successfully at the ALS to
generate high-intensity photon beams with variable photon
polarization (from linear to circular). However, users were
not completely satisfied with the EPUs performance because
they degraded the beam quality by increasing the photon beam
size. Based on detailed magnet measurements, a system was
developed that maintains a constant beam size. It is now
being employed in routine user operation solving a problem
that has affected many other light sources.
New Undulator Beamline for High-Resolution Photoemission
Electron Microscopy.
Beamline 11.0.1 is a new elliptically polarizing undulator (EPU)
beamline dedicated to photoemission electron microscopy (PEEM)
at the ALS. An EPU, the third installed at the ALS, delivers
light into the new beamline, which began commissioning March
2005. With full polarization control and continuous coverage
optimized over key energy regions, this beamline will be an
attractive user facility for organic and magnetic
polarization-contrast microscopy. This beamline will have an
aberration-corrected photoemission electron microscope
(PEEM-3) with a spatial resolution of approximately 5
nanometers.
New In-Vacuum Undulator Beamline for Femtosecond X-ray
Studies.
Beamline 6.0.1 for soft x-ray science with ultrashort photon
pulses of 200 femtoseconds was ready for commissioning in
July 2005. The beamline is unique in the U.S. and will be
made available to users in FY 2006. The primary components
are a vacuum undulator to produce x-rays over a wide
photon-energy range, optical components, including a
spectrograph for recording an entire x-ray absorption
spectrum from one photon pulse, and a high-repetition-rate
femtosecond laser system.
§
The Advanced Photon Source (APS)
More Stable Beams.
Using a technique pioneered at the APS, 175 girders
supporting accelerator components in the APS storage ring
have been displaced by as much as 6 mm during scheduled
tri-annual maintenance periods over the last seven years,
eliminating the stray radiation background signals. As a
result, photon beam position monitors (BPMs) for insertion
devices over the entire storage ring circumference are now
operating on line. The APS leads the world in the use of
photon BPMs for insertion device beamlines. Use of these
monitors has improved long-term x-ray beam angular stability
by more than a factor of five. Users are able to scan the
x‑ray photon energy by changing the insertion device gap on
demand, while still maintaining superior photon beam
stability on their samples. The payoff is improved ability
to resolve micron and nanometer-sized features in samples
Improved Timing Experiments.
The x-ray pulse structure at the APS is on the order of 100
picoseconds. This pulse width enables special classes of
timing experiments where the physical phenomena require fast
time resolution. Recent experiments at the APS using this
technique have involved the study of porphyrins that may one
day form the building blocks of novel catalysts, photonic
devices, and efficient solar-power units. The APS has a
special operating mode to facilitate these types of
measurements. In this mode, a single x-ray timing pulse is
isolated from the other x-ray pulses. The intensity in the
pulse is determined by the amount of charge stored in the
isolated electron bunch that generates the photon pulse.
Recent changes to the storage ring top-up injection method,
which allows the APS linear accelerator to vary the
injection charge along with increasing the injection
frequency from two minutes to one minute, have resulted in
doubling the single pulse-intensity without adversely
affecting the non-timing experiments.
Improved Mirrors for X-ray Focusing.
Elliptically-shaped mirrors based on new technology
developed at the Advanced Photon Source are being used to
achieve unprecedented focusing of high-brightness x-ray
beams. These mirrors are especially useful for producing the
microbeams that are used to probe the composition and
structure of materials. They are being applied to studies
such as microstructural analyses of structural changes
arising from welding operations and detailed investigations
of the three-dimensional structure of complex crystalline
samples.
Nanoprobe Beamline Commissioned for First Experiments.
The world’s first hard x-ray nanoprobe was activated in
March 2005, at the APS. The Nanoprobe beamline is a central
component of the new Center for Nanoscale Materials at
Argonne National Laboratory. The x-ray nanoprobe will have a
spatial resolution of 30 nanometers or better, the highest
of any hard x-ray microscopy beamline in the world. It will
offer fluorescence, diffraction, and transmission imaging in
the x-ray spectral range of 3-30 keV, making it a valuable
tool for studying nanomaterials.
§
The National Synchrotron Light Source (NSLS)
New X-ray Micro-Diffraction Instrument.
This instrument to be used for nanoscale research was
developed at the X13B beamline to take advantage of the
small source size of the in-vacuum mini-gap undulator in the
X13 straight section of the NSLS x-ray ring. It consists of
five main subsystems: monochromator, focusing optics, sample
manipulator, charge-coupled detector (CCD) area detector,
and a point detector with two degrees of freedom. The sample
stages are equipped with integrated submicron position
encoders for excellent positional precision and
repeatability. The point detector assembly allows the use of
analyzer crystals to obtain better resolution. A key design
feature is the close attention paid to mechanical coupling
of the focusing optics to the sample positioner to reduce
vibrations and improve the microscope stability for the
users.
Elliptically-Polarized Wiggler Beamline Upgrade.
The Elliptically-Polarized Wiggler (EPW) located in the X13
straight section of the NSLS x-ray is a unique radiation
source that produces time-varying elliptically-polarized
x-rays for magnetism studies. A major upgrade was performed
on beamline X13A to enhance its performance. It included
replacement of the existing horizontal focusing mirror,
which had been plagued by poor reflectivity as well as
mechanical and thermal stability problems, with a new
water-cooled spherical mirror. The new mirror system
increases the horizontal photon collecting angle by a factor
of two and is fully motorized to allow precise manipulation
and optimization of the mirror’s position. In addition, the
beamline interlock and control systems were upgraded. The
beamline upgrade has resulted in an order of magnitude
increase in the photon intensity delivered to the sample,
and the elimination of mechanical and thermal instabilities.
These improvements have led to more efficient use of the
beamline and increased magnetic sensitivity in the
measurements.
Development of a Photon-Counting Silicon Microstrip Array
Detector.
The NSLS detector group has developed an extremely versatile
1-dimensional position sensitive detector. It is based on
custom microelectronics developed at Brookhaven National
Laboratory, and consists of a linear array of silicon
photodiodes, each 0.125 x 4 mm, which is connected to a set
of 32-channel custom integrated circuits and a
microprocessor system. The detector system’s performance is
several orders of magnitude better than one can achieve with
charge-coupled type detectors. It is easily adaptable to as
large an array as is needed by the application. For example,
arrays of 320 and 640 strips, 40 and 80mm long have been
fabricated for real-time x-ray scattering.
X-ray Ring Lattice Symmetry Restored.
The most direct benefit for the NSLS user community was the
restoration of the x-ray ring magnetic field lattice
symmetry, which for many beamlines resulted in a 25 percent
reduction of the horizontal beam size and an increase in
photon intensity delivered to a sample. The desired eight
fold symmetry of the x-ray ring magnet lattice can be lost
from errors in the x-ray ring quadrupole field strengths.
The quadrupole errors can be partially compensated by trim
coils available in the x-ray ring for one of the quadrupole
magnet families. These errors were determined from an
elaborate analysis of the electron orbit measurements taken
as quadrupole magnet field strengths were systematically
varied. This improvement allowed the NSLS to restore the
eight fold symmetric x-ray ring magnet settings for routine
operations.
§
The Stanford Synchrotron Radiation Laboratory (SSRL)
First SPEAR3 Run Completed.
In the commissioning run for the new SPEAR3 accelerator, the
facility proved to be exceptionally reliable, providing very
stable beam for a very high percent (97) of the scheduled
time. This is higher than ever recorded with SPEAR2, and an
exceptional achievement for a new storage ring. The user run
commenced in March and the SPEAR3 storage ring operated at 3
GeV/100 mA and provided 30+ hour life times. (The average
uptime over the past five years was 96%.) During the run,
users on 239 different proposals received beam time in a
total of 466 experimental starts involving 1,516
researchers.
First High-Current SPEAR3 Tests Performed.
SSRL conducted three special 8-hour shifts of SPEAR3
operation with currents above the official safety envelope
value of 100 mA. These high-current test shifts took place
on swing shifts with the experimental floor cleared of
non-radiation workers. The main purpose of these tests was
to determine if multi-bunch electron beam instabilities will
be encountered at higher current operation, in which case a
program to implement a costly multi-bunch feedback system
would have to be launched. Other potential problems,
primarily excessive component heating, are also of concern.
The current reached in these tests was limited to 225 mA by
the power rating of some absorbers in a legacy insertion
device chamber. This current was reached and a comprehensive
search revealed no apparent beam instabilities.
New Methods Developed for Studying Structures of
Nanomaterials.
The reactivity and properties of nanomaterials are highly
influenced by particle size and atomic-scale structure.
Researchers at SSRL have recently demonstrated that the
combined use of several x-ray scattering and absorption
measurement techniques leads to quantum leaps in
understanding the structures of nanomaterials. X-ray
scattering measurements allow experimenters to combine size
and shape information with structural information to remove
the small-particle size contribution to x-ray diffraction
peak broadening, whereas x-ray absorption measurements
provide complementary, metal-specific information on local
atomic structure in disordered materials. Measurements on
zinc sulfide have conclusively demonstrated that structural
relaxation of surface atoms causes inhomogeneous internal
strain, markedly altering its material properties. This
multi-technique nano-characterization approach has further
been advanced by developing methods for the routine
characterization of bacterial nano-minerals under
fully-hydrated in-situ conditions. Bacterial nanominerals
are an important class of naturally occurring nanomaterials
that help to control the composition of the atmosphere, the
potability of natural waters, and the arability of soils.
This multiple-technique method provides unique information
of wide interest to the nanoscience community.
§
The Intense Pulsed Neutron Source (IPNS)
Simultaneous Measurement of Mixed-conductor Lattice
Relaxation, Diffusion, and Gas Conversion.
The General Purpose Powder Diffractometer (GPPD) at the IPNS
is equipped with a specially designed controlled-atmosphere
furnace, where samples in pellet or hollow-tube form are
exposed to mixtures of gases to control oxygen and hydrogen
content from highly oxidizing to highly reducing
environments. Using two separate gas delivery “circuits,”
simulated membrane operation conditions can be achieved
whereby the responses of oxygen-permeable membranes to
strong oxygen partial pressure gradients can be studied.
Exhaust gases are analyzed with a Residual Gas Analyzer to
probe for leakage and to quantify gas conversion reactions.
Dense ceramic components with mixed-conduction properties
and high oxygen permeability are important as membranes for
oxygen separation and solid oxide fuel cell applications.
Membranes are typically operated at elevated temperatures
(800-1000°C) and exposed to large oxygen partial pressure
gradients. This experiment reproduces the conditions under
which these membranes will be used commercially and provides
insights into the unusual differential oxygen partial
pressure stability of these materials.
Accelerator Systems Improvements.
Efforts include: completion of the beamline-magnet power
supply upgrades, replacing the originals with
higher-efficiency and better regulated units; completion of
a full year of operation of the first of two new
kicker-magnet power supplies; and completion of full-power
tests of the new third-rf system that will be installed in
the synchrotron ring to provide new proton beam capture and
handling capabilities.
National Neutron and X-ray Scattering School.
During August 2005, Argonne National Laboratory again hosted
the National School on Neutron and X-Ray Scattering. The
school continues to attract outstanding graduate students
and post-doctoral appointees with 150 applications for the
60 positions available in 2005. The intensive training
introduces students to the theory of, and provides hands-on
experimentation in, x-ray and neutron scattering.
§
The Manuel
Lujan Jr. Neutron Scattering Center (LANSCE)
Neutron Scattering Winter Schools.
The First and Second Annual LANSCE Neutron Scattering Winter
Schools were held, with 30 students from a wide geographical
distribution attending each School. The 2004 topic was
magnetism and the 2005 topic was mechanical properties of
materials. During nine intensive days in Los Alamos,
students had lectures from world experts on the key
materials issues for the School theme, modeling and theory,
and neutron scattering techniques addressing these issues.
In addition, the students had the opportunity to gain
hands-on experience in neutron-scattering techniques and
data analysis.
New Sample Environments.
A major emphasis on sample environments in FY 2005 has
greatly enhanced the low temperature, high field, and high
pressure possibilities for user experiments. Investments in
new low temperature sample environments, high pressure
instrumentation, sample goniometers, and support staff have
made users more productive. Along with the 11-Tesla
superconducting magnet commissioned in 2004, the Lujan
Center’s suite of sample environments for condensed matter
physics has dramatically improved in FY 2005. A rheometer
designed to synchronize with the 20 Hz Lujan Center pulsed
neutron beam is expected to be tested in FY 2005. It will
provide a unique capability to impose accurate hydrodynamic
shear on polymer solutions and colloidal suspensions while
performing structural measurements by small-angle neutron
scattering.
Instruments Enhancement.
The High Intensity Powder Diffractometer (HIPD) and the
Single Crystal Diffractometer (SCD) have received upgrades
to software, shielding, alignments, and hardware that have
increased their neutron intensity, user throughput, and
efficiency. New hardware and software controls on the Low-Q
Diffractometer (LQD) and a new detector have made small
angle neutron scattering (SANS) more effective.
§
The High Flux Isotope Reactor (HFIR)
Common Guide Casings for Seven New Instruments Installed.
Neutron guides transport cold neutrons (energies ~0.1–20 meV)
with little loss in flux. This permits one to transport
neutron beams from the source to instruments several tens of
meters away. This lowers the instrumental background noise
from gamma rays and unwanted neutrons since one can place
the instruments far from the source. Also, the guides have a
slight curvature which removes the “line-of-sight” view of
the neutron source and further reduces this background. The
guides are made by coating glass with layered coatings
called supermirrors which are highly reflective for
neutrons. These flat, coated glass plates are then assembled
to form hollow rectangular cross-sectioned pipes with the
coated sides forming the interior walls of the pipes. These
guides will be illuminated with neutrons produced by the new
HFIR cold source to be installed early in 2006.
HB-4 Shield Tunnel and Velocity Selector Shielding
Installed.
A great deal of neutron shielding is required to shield the
exit of the new HFIR cold source and components of the cold
neutron beamlines. The first and largest general section of
shielding for the new instruments was constructed. Also, the
lead shielding for the velocity selectors for the two small
angle neutron scattering (SANS) instruments was assembled.
These components are essential for the new Center for
Neutron Scattering cold neutron spectrometers.
SANS 1 Detector Tank and Internal Components Installed.
The largest component for the first Small Angle Neutron
Scattering (SANS) instruments has been installed. This giant
tank will contain the detector for this instrument. The 1
meter square detector will ride on rails inside the
evacuated volume of the tank.
The
Neutron Reflectometer Commissioned.
A new
instrument, the neutron reflectometer, was commissioned for
use in the general user program at the HFIR Center for
Neutron Scattering. This machine is optimized for the
studies of surfaces and interfaces. It is the fifth Cold
Neutron Source instrument fully commissioned and will be
used for the studies of polymers, biomaterials, thin solid
films, and surfactants.
Selected FY 2004 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
The Ultimate Analysis: Single-Atom
Spectroscopy in Bulk Solids. A longstanding dream in
materials sciences and engineering has been to see and study those specific
individual atoms that are critical to bulk properties and to determine their
location and active configuration. Now, through an enhanced scanning
transmission electron microscope with improved optics, researchers are able to
observe an individual atom within its bulk environment and characterize its
chemical state via spectroscopic means, determining its valence and bonding with
nearest neighbors. The advance was made possible by correction of lens
aberrations in the electron microscope to give a smaller yet brighter beam with
a diameter of approximately 1 Ångstrom. Single-atom sensitivity, the ultimate
analysis, opens up all areas of materials science and engineering to fundamental
investigations in a revolutionary way
New Thin-film Texture Discovered with
Potential for Nanotech Applications. One of the most fundamental
structural properties of a thin film is its “texture,” which is the
orientation of individual grains with respect to the deposition substrate. Three
types of texture are commonly observed: random, where no single orientation is
dominant; fiber-texture, where the film grains are parallel to the growth
direction, but random about that direction; and epitaxial, where the film
orientation is fixed in three dimensions with respect to the substrate. The new,
fourth type of texture, named axiotaxy, was observed in a number of thin film
systems in which the film and substrate share a common plane orientation as a
consequence of crystal lattice matching. This new texture provides a potential
method for assembling large numbers of nanocrystals in regular patterns for
nanotech applications
Negative Refraction - New Frontier for
Superlenses.
The first demonstration of negative
and positive refraction of visible light at the same crystal interface was
recognized as one of the “Top 15 Physics News Stories of 2003” by the
American Institute of Physics. Nature provides us with optical refraction which
is always positive: that is, the incident and transmitted light through an
interface of two different media are on opposite sides of the interface normal.
For negative refraction, they are on the same side of the interface normal. The
beauty of negative refraction is total transmission and zero reflection,
regardless of the angle of light incidence. These properties lend themselves to
the creation of “super lenses.” Laser
beams can be steered in nano-photonic devices without loss, and optical
telescopes can be built with higher resolution. The new interface uses a
ferroelastic twin domain boundary such as a yttrium vanadate (YVO4) bi-crystal
and is applicable to any frequency of the electromagnetic spectrum. As a vision
for the future, electron beams could be focused more efficiently in highly
sensitive electron microscopes
Multi-band Semiconductors for High
Efficiency Solar Cells.
A new semiconductor material has
been discovered that has multiple energy gaps, instead of the usual one,
allowing for ultra-efficient energy capture of sunlight. Multi-band
semiconductors were theoretically predicted over 20 years ago, but only now
through the properties of so-called “highly mismatched alloys” (HMAs) have
they been achieved. HMAs are compound semiconductors in which a small fraction
of the anions are replaced with more electronegative atoms, producing a material
with a new band having a strong quantum mechanical interaction with either the
occupied valence band or the empty conduction band of the host semiconductor.
Using this approach it was predicted, and subsequently demonstrated
experimentally, that a II-VI semiconductor compound (ZnMnTe) with a small
fraction (~1%) of the group VI constituent, i.e., tellurium, replaced by oxygen
operates as a multiband semiconductor. Theoretical evaluation indicates that a
single junction solar cell fabricated from this material could achieve a power
conversion efficiency of 56%
Individual Carbon Nanotubes as
Nanoscale Light Sources. A single carbon nanotube with a diameter of only 1.4 nanometer was used
to fabricate the smallest source of light that can be controlled by electric
current. The emission spectrum (color) of the light varied as a function of
nanotube length and diameter. The center of the spectrum is determined by the
nanotube diameter while the width of the spectrum depends on the length of the
nanotube. Long nanotubes (50,000 nanometers) had narrow, symmetric emission
spectra (characteristic of cold electrons) centered at the bandgap of the
nanotube, which is inversely proportional to the nanotube diameter. Short
nanotubes (500 nanometers) were also peaked at the bandgap of the nanotube, but
showed broad, asymmetric spectra with a tail on the high-energy side,
characteristic of hot electrons. These spectra show the cooling of hot electrons
in nanotubes as a function of length through excitation of vibrations of the
nanotube. The demonstrated understanding and control of optical properties using
nanotubes could be important for optoelectronic nanotechnology
Magnetic Resonance Imaging at the
Nanoscale.
An innovative magnetic resonance approach to characterizing nano-porosity in a
variety of materials has been developed. Magnetic resonance imaging (MRI) has
been tremendously successful in visualizing resident deformities and the
presence of disease in soft, porous biological tissues of the liver or kidney,
yet the limited resolution precludes characterization at the nanometer scale. By
using a technique of percolating inert gas through a nanoporous structure and
then determining both the "sticking coefficient" of the gas and the
time it takes for the gas to move away from the pore structure, MRI can now
evaluate both the pore size distribution and the nature of the pore
connectivity. This allows the analysis of highly porous structures that are
present in many living systems and those created artificially in the laboratory
such as filters to sequester pollutants, catalysts for chemical reactions,
highly efficient insulators, and high strength to weight ratio materials for
structural applications. By understanding the relationship between processing
parameters and porosity of the resultant materials, advances in porous materials
can be made
Nano-Trains:
Nanoparticle Transport Using Motor Proteins.
An active transport system that can be used to pick up, transport, and deposit
nanoparticles within a microfluidic system has been developed. The active
transport system is powered by the motor protein kinesin, a naturally occurring
molecular machine. In the presence of a fuel source (adenosine triphosphate, or
ATP), the head groups in the motor proteins “walk” rapidly along protein
fibers called microtubules. With the tails of kinesin fixed to a surface the
proteins can be used to propel the microtubules across the surface. The
microtubules can now be modified to carry various size particles, ranging from
10 micrometers to 10 nanometers, and in large quantities, by functionalizing
segments of the microtubules to carry cargo, like train “cars,” while
leaving other segments unfunctionalized to act as “engines” by allowing free
interaction with the motor proteins. This discovery suggests that highly
non-equilibrium structures could be developed using the same active transport
strategies that organisms employ for tissue assembly and muscle actuation
How Do Complex Fluids Jam?
Is the mechanism for flow jamming the same for solid particulate matter (such as
powders, coal, grain, pills, etc.) as for foam (bubbles in a fluid)? Two
processes that rely on flowing foam are oil extraction and mineral separation. A
major feature of both is that the flow can spontaneously stop, or jam, as the
bubbles block each other. A better understanding of the causes of jamming will
improve processes relying on flow. Recent studies using model foam systems have
measured the coexistence between a flowing phase and a jammed phase. A
surprising result was that this behavior was different from jamming observed in
solid particulate systems. It provided evidence for at least two different
mechanisms of jamming, a critical step in furthering the understanding of the
jamming process
Electron Transport in Semiconductor
Quantum Wires.
Spintronics (electronic phenomena that depend on electron spins) may provide a
route to future generations of high-speed, low-power, nanoelectronics and may
open up new areas of technology such as solid-state-based quantum computing.
Significant challenges exist to realize these goals, including how to detect –
or read – the electron spin in an electrical measurement. It has recently been
demonstrated how such detection can be achieved in practice by exploiting the
unique features of electron transport in semiconductor nanostructures known as
quantum wires. Experiments show that the spin state of one quantum wire can be
detected by studying the conductance of another wire located in close proximity.
Theoretical work supports the idea that these experiments provide non-local
detection of the electron spin opening pursuit of applications of this work to
solid-state approaches to quantum computing
Superfluid Excitons at High Magnetic
Field.
A grand challenge for condensed matter physics is the observation of a new phase
of matter created by the “condensation” of excitons, which are electron-hole
pairs. Because excitons are bosons, any number can occupy a single quantum
state. Thus, at low temperature, they should condense into the lowest energy
level. Unfortunately, observation of this has been hindered by the rapid
recombination of the electron and hole. Using magnetic fields to create stable
exciton gases in doped double-layer semiconductor structures, the first evidence
for condensation of an exciton gas was found in quantum tunneling measurements.
The signature of the condensation was that both the conventional and Hall
resistances of the sample become extremely small at low temperature. This
nascent superfluidity is the strongest evidence yet for excitonic Bose
condensation
Going from Good to Great:
Doubling the Superconducting Upper Critical Field of Magnesium Diboride. In January 2001, a simple compound, magnesium
diboride (MgB2) was discovered to superconduct at a remarkably high
temperature of 40 K, double the 20 K value for the niobium-based industrial
standard. However, in its pure form, the material stops superconducting in a low
magnetic field. During the past year, it was determined that the material
continues to be superconducting in high fields if a small amount of carbon,
about 5%, is substituted for boron. This has led to a better understanding of
the superconductivity in this unique compound. The results indicate that, if the
current carrying capability and mechanical properties can be further enhanced,
carbon-doped MgB2 could become the next industrial standard
superconductor -- better, cheaper, and lighter than niobium alloys
Wiring for Nanocircuits: Stabilized
Silicon Nanotubes.
Recent theoretical predictions have indicated that silicon nanotubes can be
stabilized by attaching a string of 3d transition elements along the outside of
the tube. These same calculations predict that the resulting nanotubes will be
strongly conducting -- an important property needed by a candidate material for
wiring together nanoelectronic components. The often considered carbon
nanotubes, however, can be weakly metallic, semiconducting, or insulating
depending on a property that is quite difficult to control-the winding ratio of
the tube. The stabilization and metallization of the silicon nanotube can be
accomplished with a small amount of nickel, about one nickel atom for every five
silicon atoms. The compound tube structure studied is also smaller than most
carbon nanotubes
Lashing Together Nanoparticles to Make
Real Things.
Theorists have shown that one can cause nanoparticles to self-assemble into
ordered arrays by attaching short polymer strings to the particles to act as
tethers. This is important because it is necessary to assemble large numbers of
nanometer-sized particles to create something of size appropriate to our world.
It must be done as a loose assembly of the nanoparticles to retain their special
properties but often also be arranged in special geometric patterns to realize
the desired property. The technique demonstrated by detailed simulations is to
attach short polymer strands to the particles at specified points and then let
nature take its course. While currently only a theoretical prediction, the
scheme is quite feasible and is expected to be in use within two to five years.
In the meantime, the theorists are busy developing a “handbook” of how to
position the tethers, how long they should be, and what they should be made of
to accomplish a particular desired structure
A New Class of White Light Phosphors:
Advancing the Solid State Lighting Initiative. A new class of tunable, white light emitting
phosphors based on single size semiconductor nanoparticles or quantum dots (QDs)
has been discovered. This breakthrough meets one of the most critical needs in
the Department’s Solid-State Lighting Initiative, whose aim is to replace
present day highly inefficient light bulbs by solid state lighting devices and
thereby have revolutionary effects on conserving electric energy. This
accomplishment was made possible by the finding that, for sufficiently small
cadmium sulfide and cadmium selenide QDs of diameters two nanometers or less,
the onset of light absorption (determined by dot size) and the emission energy,
or color (determined by interfacial chemistry), can be independently controlled.
The decoupling of these two features allows wide separation of the absorption
and emission to eliminate self-absorption of the emitted light, and allows one
to tune the emission throughout the visible range from a population of
single-size dots. Key to this discovery is the ability to tailor the energies
and lifetimes of interface states by the addition of suitable surfactants that
bind to selected sites on the QD surface (which determine the emission), or the
addition of suitable electron or hole traps (e.g., zinc or sulfide ions,
respectively)
Catalyst Active Sites Imaged in Real
Time.
The atomic-scale formation and dynamics of active sites on a catalytic surface
have been imaged for the first time. Using movies made from a series of
state-of-the-art atomic-level scanning tunneling microscope images, the
time-dependent behavior of sites on the surface of palladium metal was observed
while diatomic hydrogen gas was adsorbed and then dissociated into two hydrogen
atoms. The catalytic dissociation of hydrogen on a metal surface is pervasive in
catalytic chemistry. Contrary to the prevailing view of the past three decades,
it was found that three adjacent and empty surface sites are required for this
process to occur - two empty sites are not sufficient. This surprising result
calls into question the conventional thinking on the structure of active sites
on catalyst surfaces. Further real-time measurements will help establish the
molecular-level understanding of the formation of the active sites that
determine the catalytic activity of a surface
Basic Research Leads to Terabit Memory
Devices.
A decade-long basic research project has led to the first successful application
by industry of a novel approach in nanotechnology, ‘molecular
self-assembly,’ to enable continued miniaturization of semiconductor circuitry
such as FLASH memories. The essential element in this new approach lies in
directing the orientation of highly-dense arrays of nanoscopic cylindrical
domains in thin films of diblock copolymers (BC). Using routine lithographic
processes, the BC films are transformed into large area arrays of cylindrical
nanopores with very high aspect ratios. Establishing the ability to produce such
high density arrays in a simple, robust, and inexpensive manner using
conventional processing (new tooling is not required and will not be required
with further advances in the self-assembly technique) has broken new ground in
fundamental studies of nanoscience and the rapid transfer of this technology to
the industrial sector
Fundamentals of How Liquid Metals
Solidify Answered with Synchrotron Radiation Experiments. Materials properties are determined, in large
measure, by the nature of the solidification process. During the cooling
process, the metal atoms in the liquid phase are thought to pack together with
almost the same order as the resultant solid. In fact, early experiments
demonstrated that liquids cooled far below their melting point still maintain a
large degree of disorder. As the temperature is further lowered, a well ordered
crystalline solid is eventually reached, but the nucleation pathway to the
crystalline form remained a mystery. By combining levitated molten metal drops
with a newly developed, in-situ synchrotron x-ray diffraction technique for
measuring structure during solidification, investigators have verified for the
first time that atoms in a liquid metal arrange themselves with the local
symmetry of an icosahedron, a Platonic solid consisting of 20 tetrahedra
(4-sided pyramid shaped polyhedra). As cooling proceeds, the icosahedral
arrangement transitions to the final crystalline form. This discovery proves
that atomic scale structure in the liquid actually plays a role in
crystallization, something that is not treated in current nucleation theory
X-Ray Microscopy in 3D on a Micron
Scale.
Metal deformation, ranging from the centuries old heating and beating of sword
edges to the rolling of metal sheets in modern industrial mills, is one of the
oldest and most important materials processing techniques, yet it remains one of
the least understood. Although elaborate recipes have been developed to produce
alloys with desired properties, they are all based on expensive and inefficient
search and discovery methods. To address this, a new, nondestructive,
submicron-resolution 3D x-ray microscopy technique with high-precision nanoscale
indentations to study the fundamental aspects of deformation in ductile
materials has been developed. X-ray microscopy measurements made using
penetrating synchrotron x-ray microbeams are providing detailed, quantitative
information on the deformation microstructure for sizes below that of a human
hair, but too large for electron microscopy. These results provide previously
missing information that is critical for testing advanced theories and computer
modeling and for making new materials, with predictable properties, in a more
efficient manner
Understanding Fundamental Magnetic
Properties Could Lead to Sensor Development. Magnetic excitations provide insight into the spin
structure and spin dynamics of materials. One material studied exhibits colossal
magnetoresistance, a property that makes it interesting for sensor applications.
The magnetic structure of this material (Pr0.5Sr0.5MnO3)
was determined to be ferromagnetically aligned layers that are coupled
antiferromagnetically. The magnetic excitations (also called spin waves) were
measured using inelastic neutron scattering at the High Flux Isotope Reactor at
Oak Ridge National Laboratory. The spin wave dispersion follows the behavior
expected from linear spin wave theory. With refinements in analyzer efficiency
and film preparation techniques, the measurement technique will then be applied
to thin films. This should allow a search for spin wave excitations in
antiferromagnetic films of Fe-Pt.Bos
Chemical
Sciences, Geosciences, and Energy Biosciences Subprogram
Potential for Greatly Enhanced
Efficiency in Nanocrystalline Solar Cells. An incident solar photon
striking a semiconductor solar cell normally produces a single electron-hole
pair (exciton) and some excess heat. Experimentalists have recently demonstrated
that two or more excitons can be created by absorption of a single photon in an
array of lead-selenide nanocrystals. This process is called “impact
ionization” and is observed when the photon energy is greater than three times
the band gap of the nanocrystal. Multiple excitons from a single photon are
formed on the picosecond time scale, and the process occurs with up to 100%
efficiency depending on the excess energy of the absorbed photon. If this
process could be translated into an operational solar cell, the gain in
efficiency for converting light to electrical current would be greater than 35%.
High Order Harmonic Generation
Using Ions. High harmonic generation (HHG) is a process in which highly
nonlinear optical effects, driven by ultrafast, intense laser pulses in an
atomic gas, are used to turn visible bursts of photons into bursts in the
extreme ultraviolet and soft x-ray spectral regions. There is a cutoff at high
frequencies for HHG that is determined by the ionization potential of the atom
and by defocusing and phase mismatch of the pump-laser beam due to ionization.
Recent experiments have significantly extended the range of HHG to photon
energies up to 250 eV through the use of atomic ions, which have higher
ionization potentials and are thus capable of producing more energetic harmonic
orders. In this work an ultrashort, intense optical laser pulse was focused into
a hollow fiber filled with low-pressure argon gas. The fiber serves as a
waveguide to phase-match the fundamental excitation pulse with the HHG soft
x-ray pulse. This work demonstrates that HHG from ions can extend laser-based,
coherent up-conversion into the soft x-ray region of the spectrum.
Manipulation of Carbon Monoxide
Oxidation to Carbon Dioxide. The formation of a chemical bond involves
the approach of two reactants to short distances so that a new bond can form.
How close do the two reactants need to be for them to interact with each other?
In this novel experiment, a single carbon monoxide (CO) molecule on a surface
was pushed toward two oxygen (O) atoms that were formed in the dissociation of O2
by tunneling electrons. Using inelastic electron tunneling spectroscopy in a
cryogenically cooled microscope, the hindered rotational mode of the CO molecule
was measured as its distance from the two O atoms decreased. The change in this
vibrational energy signaled the onset of a significant CO-O interaction prior to
the formation of carbon dioxide (CO2). A shift of 20% in the hindered
rotation energy was observed when the CO molecule was within 2.50 Å from each
of the two O atoms. Spatially resolved mapping of the hindered rotational mode
led to a tilted CO in the O-CO-O complex. The controlled positioning of the two
reactants allowed direct visualization of the chemistry. This research probed
individual reactive encounters of the type that constitute a surface-mediated
catalytic process. Exacting control of catalysis will require such
molecular-level characterization.
Direct Numerical Simulations of
Homogeneous Charge Compression Ignition. Homogeneous charge compression
ignition (HCCI) has the potential to reduce nitrogen oxide and particulate
emissions from internal combustion engines while improving overall efficiencies.
A major challenge posed by this method of combustion is control of the heat
release rate, and in particular, a means to spread the heat rate out in time to
suppress the occurrence of damaging engine knock. Direct numerical simulations
(DNS) of lean hydrogen-air ignition at high pressure and constant volume in the
presence of temperature inhomogeneities are helping researchers understand the
HCCI combustion process. Starting from an initial distribution of fluctuating
temperatures at high pressure, the evolution of localized ignition sites was
studied in a constant volume DNS with detailed hydrogen/air reaction kinetics.
For the first time, numerical simulations revealed that flame front and
spontaneous ignition propagation can coexist in this environment. The
simulations showed that the local nature of the ignition propagation is
primarily dependent upon the inverse of the local temperature gradient. Criteria
were developed from the DNS data (e.g., speed of the ignition front and a
critical temperature gradient at the front) to distinguish between the different
modes of propagation.
Charge Separation by Carbon
Nanotube/Ferrocene Nanohybrids. Carbon nanotubes, which are chemically
stable and electrically conducting, have been modified for the first time by
attachment of electron donors, in this case, ferrocene molecules. When excited
with visible light, these carbon nanotube-ferrocene hybrids exhibit
intramolecular electron transfer to yield long-lived charge-separated species.
The carbon nanotube serves as the electron acceptor in the donor-acceptor
ensemble, distributing the charge over its extended π-electronic system.
The separation of charge is sufficiently long lived to show promise for future
development of solar photoelectrochemical cells based on modified carbon
nanotubes.
They Bend Before They Break:
Fast Scission of Chemical Bonds. Bond-breaking reactions in
liquid solution which are so fast that the rates could not previously be
measured, have recently been studied at the new picosecond Laser-Electron
Accelerator Facility (LEAF) at Brookhaven National Laboratory. A large class of
molecules known as aryl halides was studied, in which a halogen atom, such as
chlorine or bromine, dissociates from a sizable planar ring structure, breaking
its bond. The newly measured rates can only be explained theoretically if the
bond breaks by the halogen atom bending out of plane by about 30 degrees before
bond breaking, in a bent transition state. Such fundamental knowledge of the
reaction mechanism may lead to improvements in energy efficiency and fewer toxic
by-products in large-scale industrial processing.
Protein-Nanoparticle Hybrid
Systems for Light Energy Conversion. Novel protein-nanoparticle hybrid
assemblies have been developed that employ semiconductor nanoparticles for
initial light-induced charge separation and biomolecules for subsequent
chemical/electrical conversion. The end-to-end, wire-like nanorod structures are
based on nanoscale metal oxide particles, in which the ability to systematically
manipulate size and shape of the nanoparticles was exploited in synthesis of
axially anisotropic tubes, cubes, rods, or stars. The nanoparticles were
oriented into organized architectures using biolinkers, such as the biotin
molecule, that bind strongly to the protein, avidin. Photoexcitation of the
wire-like architecture resulted in charge separation originating at the tips of
the nanorods: the photogenerated electrons being localized at the semiconductor,
and holes at the protein. Thus, a rational design of protein-nanoparticle hybrid
architectures enables coupling of photoinduced charge separation in
nanocrystallites with the charge-transfer induced chemistry on proteins. The
hybrid architectures and ensuing chemistries can either use or alter protein
functionality, and could be used for construction of solar-based molecular
machines.
Reverting Carbon Dioxide into
Valuable Chemicals. An inexpensive, low-temperature synthetic route for
the conversion of carbon dioxide into useful chemicals and fuels is a
long-standing challenge. Despite extensive research, current catalysts still use
expensive complexes of platinum-group metals. Recent work has led to a
breakthrough in the catalytic addition of hydrogen to carbon dioxide to produce
formic acid. Using sophisticated high-throughput techniques to rapidly search
for promising catalytic structures, investigators have identified the broadest
range to date of hydrogenation catalysts that can sustain high activity for many
cycles. These structures consist of phosphine-complexes of copper, chromium,
iron, indium, molybdenum, niobium, nickel, or tungsten, all of which are
abundant and inexpensive metals. Detailed structural and mechanistic studies
have led to even further improvement of the activity and durability by
surrounding the metal centers with ligands designed to provide optimum
electronic structure while protecting the metals from degradation. The new
nickel, copper, and iron phosphine-cyano complexes carry out the production of
formic acid at 40 bar and 50 oCelsius with limited deactivation for
periods of days.
Pure Hydrogen from Alcohol through
Microsecond Catalysis. Researchers have recently shown that it is
possible to selectively extract pure hydrogen from ethanol, a renewable fuel
made from biomass, in a matter of microseconds. The process is based on a
high-temperature ceramic catalyst containing rhodium metal and cerium oxide. At
about 800 oC, wet ethanol, contacted with the catalyst for about one
microsecond, undergoes oxidative dehydrogenation to hydrogen and carbon dioxide,
with 95% conversion and 100% selectivity to hydrogen. This remarkable catalytic
performance and the low-cost wet alcohol source could result in an economically
feasible hydrogen production process for the future, especially as many of these
very rapid oxidation reactions are self-sustaining even at 800 oC or
higher and do not require external heat sources. Advances in this hydrogen
production process might provide an alternative to steam reformation of
hydrocarbons as a source of hydrogen.
Benign Polymerization Chemistry
Leads to New Polymers. The demand for polymeric materials continues to
rise at an impressive rate and, in the near future, environmental conservation
may become a major constraint in this expansion. Researchers have long pursued
catalysts that take molecules derived from biomass, such as sugars, alcohols,
and esters, and convert them with high yield and no waste into synthetic
plastics, such as polyethers, polyesters, and polycarbonates, with controlled
characteristics. Besides having appropriate thermal and mechanical properties, a
significant fraction of future polymers should be biodegradable or biocompatible
for use in large-scale packaging or in smaller-scale biomedical applications:
drug release membranes, synthetic tissue, and sutures. Recently, investigators
have successfully synthesized a family of metal alkoxide catalysts that produce
polyesters and blends via ring-opening polymerization of cyclic esters derived
from renewable sources. Examples are the synthesis of polylactides from lactides
derived from corn and the formation of polycarbonates by ring-opening
copolymerization of epoxides-oxiranes and carbon dioxide. The latter is a
chemically benign alternative to the current technology for polycarbonate
synthesis that uses phosgene, a highly poisonous gas. Through mechanistic,
microstructural, and kinetic studies, these investigators are arriving at
fundamentally new rules and new catalysts for transformations of oxygenated
molecules that may dramatically change the landscape of polymerization
chemistry.
Fundamental Studies on Crown
Ethers Benefit Cleanup of Nuclear Waste at Savannah River. Fundamental
research has provided the foundation enabling innovative technology for
nuclear-waste cleanup at the Savannah River Site (SRS). In early 2004, a large
contract was awarded for the design, construction, and commissioning of the Salt
Waste Processing Facility (SWPF) to clean up a major portion of some of the
nation's most dangerous Cold War era nuclear waste stored at the SRS.
Approximately 34 million gallons of waste from nuclear-weapons production are
stored in tanks at the SRS. Over 31 million gallons of that waste is solid or
dissolved salts in which the fission product cesium-137 comprises more than 98%
of the total radioactivity in the salt. In 2001, the Office of Environmental
Management chose the Caustic-Side Solvent eXtraction (CSSX) process developed at
Oak Ridge National Laboratory for removing cesium-137 from the waste in the
SWPF. The selection followed an intensive period of evaluating candidate
technologies by a multi-site team of scientists and engineers over a four-year
period. Selection was based on the ability of candidate technologies to meet
difficult processing requirements, including the ability to remove 99.9975% of
the cesium-137 from the waste. Such extraordinary performance requires
extraordinary chemistry, which had its roots in fundamental research which
focused on the principles of host-guest chemistry, emphasizing the synthesis of
tailored molecules that selectively bind (or host) target species. The
understanding of host-guest chemistry from this research led to the ability to
design the synthesis of crown ethers with appropriate architecture to complex
with alkali metal ions to effect extraction with high selectivity.
Improved Analysis for the Next
Generation of Electronic Devices. New research has shown that by
covalent Fluorescent Labeling of Surface Species (FLOSS), the inherent
sensitivity of fluorescence spectroscopy can be exploited to identify and
quantify low concentration functional groups on surfaces. FLOSS enables the
detection of surface chemical groups as low as 1011 molecules/cm2
(0.01% of the surface) by specific covalent attachment of fluorescent
chromophores to surface functionalities. Advances in electronics and sensors
have been made by decreasing the size of the components making electronics
faster and sensors more sensitive and selective. These advances provide an
important step in our ability to control size and thickness of insulating layers
for modern electronic devices. The technique used to develop these films is to
expose the surface, such as silicon, to a long chained molecule, and allow it to
self assemble on the surface. The length of these chains can then be reduced to
control the resistivity by reaction with electrons or ozone, and the pattern
they make on the surface can be controlled by ion or electron bombardment using
a mask or laser ablation by rastering the beam across the surface. Understanding
and controlling the chemistry of these reactions is critical to make the next
generation of devices.
Building Polar Actinide Materials.
Compounds that adopt polar structures are able to exhibit a wide range
of important technological properties such as second-harmonic generation
(nonlinear optics), piezoelectricity, and pyroelectricity. One strategy for
constructing polar structures is to use oxoanions containing heavy atoms such as
selenium, tellurium, and iodine. These oxoanions share a common feature: they
contain a nonbonding pair of electrons that can be aligned during crystal
formation to create polar structures. These anions have been combined with the
actinide elements uranium, neptunium, and plutonium to create novel polar
actinide materials. Some of the neptunium compounds are further unusual in that
the distance between neptunium atoms within the crystals can be controlled,
allowing magnetic interactions to take place between the actinide elements. This
work allows detailed structure-property relationships to be developed in polar
actinide materials. These relationships elucidate the properties of 5f
electrons, which contribute uniquely to the bonding in actinide materials and
provide models for polar materials of nonradioactive transition metals.
Plutonium Oxide Unraveled. A
collaboration of research groups has developed sophisticated quantum chemistry
software to model the electronic properties of actinide materials. These
computational programs solve the first-principles, basic equations governing the
quantum mechanics of electrons and nuclei, to yield predictions about conducting
properties, equilibrium structure, and other electronic properties of materials
like plutonium oxide (PuO2). In a recent series of calculations on a
cluster of high-performance computers, it was predicted for the first time that
PuO2 is an insulating material with a band gap of a few eV and with
ferro- and anti-ferromagnetic phases in close energetic balance. These results
are consistent with subsequent experimental data obtained by other researchers.
A successful description of electronic properties of PuO2 is a
prerequisite for more elaborated modeling of the interaction of PuO2
surfaces with water and other environmental species. Understanding these basic
processes is essential to predict the long-term stability of PuO2
when it is exposed to air, water, and other common substances.
Bioelectrochemistry on
Nanostructured Surfaces. A defining feature of modern
bioelectrochemistry is extraction of functional biomolecules and their
reconstitution on patterned surfaces in defined geometries. The
bioelectrochemical process of solar energy absorption and subsequent conversion
of light energy uses two molecular reaction centers operating in series,
Photosystems I (PSI) and II (PSII). Photon absorption triggers electron transfer
reactions that generate an electric voltage. It is this electrochemical
potential that is the source of free energy for conversion of light energy into
chemical energy. It has been demonstrated for the first time that PSI molecules
can be oriented by elementary dipole forces that exist at the air-water
interface and the dipole points predominantly towards the water. Orientation was
demonstrated by measurement of the magnitude and sign of the electrostatic
potential above the PSI-containing air-water interface. Bioreaction centers
supported in nanoporous media enable the construction of bioelectrochemical
systems for both basic and applied needs.
Thermophysical Properties of
Macromolecular Systems in Nanoscopic Structures. An important part of
nanotechnology is to understand whether the properties of polymeric systems in
nanoscopic structures are different from those of the bulk. Theoretical studies
have established for the first time that nanometer-length structures of polymer
glasses exhibit a glass transition temperature which is significantly lower than
that of the corresponding bulk polymer. These studies also established that the
elastic properties of the polymer in such structures are considerably
“weaker” than those of the bulk. Finally, and perhaps most importantly, it
has been demonstrated that the elastic moduli of nanoscopic polymeric samples
are highly anisotropic, raising serious concerns about the applicability of
continuum-mechanics computational approaches for study of such systems. These
predictions indicate that the mechanical stability of features smaller than 50
nm is severely degraded. Extrapolation of current technology as applied in the
microelectronics industry might not be possible.
Structure of Electric Double Layer
at the Rutile Surface from Molecular Dynamics Simulations. Rutile
(a-TiO2)
is the protective surface phase that will cover the drip shields over the waste
canisters at the Yucca Mountain waste repository. It is also an important
mineral in the chemical and materials industries as a catalytic substrate,
photocatalyst, pigment, and ceramic raw material. Molecular simulation of the
structure of the relaxed rutile (110) crystal surface in contact with aqueous
solutions were performed to determine the structure of water molecules near the
interface, adsorption of ions, identification of several modes of binding of
adsorbed ions with surface oxygens, and static and dynamic properties of the
surface. Quantitative experimental data provided by synchrotron x-ray
investigations determined the distribution of adsorbed water molecules and
cations at the rutile (110) surface and verified the predictive capabilities of
the computational approaches. Computational chemical physics demonstrated the
utility of classical models of the macroscopic properties of the electric double
layer. Solid-liquid surface properties (colloidal stability, structure of
micelles, membranes, metallurgy, chemical sensors, catalysis, and synthesis of
nanophase materials) can now be linked to the atomic-level structural
information.
Water-Driven Structural
Transformation in Nanoparticles at Room Temperature. Natural
mineralogical nanoparticles exist at ambient temperature, pressure, and humidity
in the geosphere. Research on nanoparticulate mineral phases provides
understanding of the role of natural nanoparticles and in predicting what the
future of “new” nanoparticles will be in the environment. Zinc sulphide
nanoparticles (~3nm, 700 atoms) synthesized in methanol exhibited a reversible
structural transformation accompanying methanol desorbtion. The binding of water
to the as-formed particles at room temperature led to a dramatic structural
modification, significantly reducing distortions of the surface and interior to
generate a structure close to that of the mineral sphalerite. This shows one
route for post-synthesis control of nanoparticles structure, and the potential
use of the nanoparticles’ structural state as an environmental sensor. The
results also demonstrate that the structure and reactivity of natural
nanoparticles will depend both on the particle size and on the nature of the
surrounding molecules.
A Molecular Switch Controls Cell
Identity. Like its fuzzy,
dwarf namesake from the “Star Wars” movie, the YODA (YDA) mutant in
Arabidopsis is small but powerful. Recent molecular genetic experiments reveal
that YODA acts as a negative regulator of plant cell fate decisions following
asymmetric cell divisions. This regulation is essential for establishing normal
cell patterns for stomata, tiny surface pores in leaves and shoots. Pore size is
regulated by a pair of flanking guard cells that serve as gas valves controlling
carbon dioxide and water vapor movement in or out of the leaf. Early in
development these cells make an irrevocable decision on whether they will end up
as epidermal cells, or undergo an asymmetric division and become guard cells.
YODA’s kinase activity sends the signal that decides this developmental fate,
thus determining the number of stomates on a leaf surface. So as plants grow and
form new leaves, they can adjust to factors such as carbon dioxide, and water
and light availability by changing stomatal density and distribution. This
illustrates how protein-gene interactions within complex regulatory feedback
loops and pathways can be deciphered to understand how a group of cells can
grow, develop, and adapt to an ever-changing environment in the coordinated form
of a whole plant.
Structural and Functional Analysis
of a Minimum Plant Centromere. Every chromosome, the carrier of
hereditary information in all living organisms, contains three essential
elements: the telomere ends, the origin of replication that initiates copying of
genetic information, and the centromeres that direct the partitioning of
chromosomes during cell division. Scientists have made a startling discovery
about the nature of these centromeres in rice plants. Their sequencing of the
centromere of rice chromosome 8 revealed the presence of four active, expressed
genes. This discovery refutes long-held scientific beliefs that centromeres
contained only structural information for chromosome segregation, programmed
within vast stretches of “junk DNA” consisting of repetitive, rearranged and
noncoding sequence tracts. This work, significant for being the first completely
sequenced plant centromere, complements the international effort to complete the
sequence of the rice genome, and represents the first step toward achieving such
practical applications as the creation of artificial chromosomes for precision
plant engineering.
The Glass Bead Game of Molecular
Detection. A significant
challenge in the study of biological systems is the ability to detect molecular
interactions with sensitivity and accuracy. Scientists have developed a novel
technique for detecting substrate binding to proteins embedded within cellular
membranes. Their technique uses the fundamental qualities of colloidal
particles, which self-assemble into a variety of ordered phases in a manner
driven by the pair interaction potential between particles. Colloidal
suspensions of membrane lipids linked to a specific substrate were coated onto
silica beads. When a protein binds to this immobilized substrate, it causes
small perturbations on the membrane surface that result in visible
reorganization of the colloid, such that the coated beads disperse. The ability
to sense molecular interactions without the use of expensive fluorescent probes
has practical implications for rapid, high-throughput screening of a variety of
interactions between biological molecules.
Selected FY 2004 Facility Accomplishments
§
The
Advanced Light Source (ALS)
New
Insertion Device Installed for Ultrafast X-Ray Pulses. Light from a high-power, ultrafast laser will travel with the electron
beam through the new permanent-magnet wiggler at the ALS, thereby modulating the
energy of a portion of the electron beam. The energy modulation results in a
spatial separation of the modulated slice of the beam, which is only 200
femtoseconds long, so that it can be used to generate ultrafast x-ray pulses for
experiments at photon energies from 100 eV to10 keV.
High-pressure
Facility Enables State-of-the-art Geophysics and Materials Research.
At the newly commissioned ALS research facility, x-rays from a superconducting
bend-magnet source, a high-efficiency micro-focused beamline, and a high-power
laser-heated high-pressure cell (diamond anvil cell) will be used for a wide
range of experiments, such as determining the high-pressure/high-temperature
phase diagrams and equations of state of materials at pressures up to the Mbar
range and at temperatures up to several thousand Kelvin.
New
Research on Solvated or Buried Systems Possible.
Real-world materials that inhabit wet environments or are buried in the interior
of more complex structures pose challenges to researchers. In
situ electronic and structural properties of such materials are now
accessible due to the high brightness of third-generation synchrotron radiation
sources and the development of liquid-cell sample chambers. The technology
developed at the ALS has already been demonstrated for the characterization of
nanoparticles and opens the way for studies of advanced battery and hydrogen
storage material.
Fast
Orbit Feedback Stabilizes Electron Beam Position. Today’s synchrotron radiation instrumentation requires that the
position of the illuminating x-ray beam be rock solid, which in turn imposes the
same condition on the position of the electron beam. ALS scientists and
engineers have commissioned a new feedback system (fast orbit feedback) that
senses the beam position and sends signals to the control system to correct any
vertical and horizontal position errors to within 2 µm and 3 µm, respectively.
§
The
Advanced Photon Source (APS)
A New Technique for Understanding
Materials under Extreme Conditions.
Nuclear resonant inelastic x-ray scattering and extreme-brilliance x-ray beams
are being used to measure, for the first time, the velocity of sound in tiny
samples of materials under extreme conditions. The ability to obtain detailed
information from minuscule amounts of materials under extreme conditions is
critical to many experiments, from geophysics to national security.
Taking the Heat from
Higher-Brightness X-rays. Two new beamlines
require two or three in-line undulators to achieve the required high photon
intensity. To accommodate the expected higher APS storage ring beam current and
concurrent heat loads that will be more than three times hotter than the surface
of the sun, a novel insertion device front end has been developed.
Powering Up to Higher X-ray Beam
Brilliance. Radio frequency (rf)
technology at the APS is one of several innovations laying the foundation for an
eventual increase in storage ring current to 300 mA. This power exceeds the rf
output power of all the TV and radio stations in a major U.S. city such as
Washington, D.C., and will provide researchers with more brilliant x-ray beams.
Glowing Results from a Unique
Application of X-ray Fluorescence. The
intense photon flux from an APS insertion device beamline has been used for the
first application of x-ray-induced fluorescence techniques to perform in-situ
measurements in high-pressure metal-halide arcs. These data, not obtainable in
any other way, are essential to developing a clearer understanding of
high-pressure arc systems, among the most energy-efficient sources of white
light.
§
The
National Synchrotron Light Source (NSLS)
Superconducting
Undulator Test Facility Constructed. A state-of-the-art cryogenic
Vertical Test Facility was designed and constructed for use in developing
superconducting undulators (SCU). This device allows precise magnetic field
mapping of superconducting undulator prototypes at cryogenic temperatures and
measures thermal performance and quench behavior under realistic operating
conditions, including simulated beam heating. A SCU design has been developed
which incorporates a novel cryogenic thermal management system to intercept the
high beam heat loads expected in future ultra-high brightness synchrotron light
sources.
Hard
X-ray Microprobe Completed for Environmental Sciences.
A new hard x-ray microprobe beamline, X27A, will provide additional and enhanced
x-ray micro-spectroscopy capabilities to the NSLS environmental science user
community. The beamline can be operated in three different modes and can focus
x-rays to a spot the size of a few microns. The detector array will enable both
elemental mapping as well as fluorescence yield x-ray absorption spectroscopy
studies of complex environmental samples.
Infrared
Spectrometer Installed on Surface Science Beamline. Corrosion and catalysis involves the interaction between gas molecules
and another material such as a metal surface. Infrared spectroscopy from metal
surfaces is an important tool for studying the interactions with adsorbed
molecules. A portion of the U4IR surface science beamline was re-built to
incorporate a new infrared spectrometer. This new spectrometer provides improved
spectral resolution, spectral range, and increased collection rates over the
previous instrument.
X-ray Beamline Renovated for Materials Sciences. The X21 hybrid wiggler x-ray beamline and two
experimental stations have been substantially rebuilt to accommodate new
experimental programs that address elastic x-ray scattering studies of materials
under high magnetic fields, thin films grown in-situ, and materials studied with
small angle x-ray scattering, with appropriate setups permanently installed in
the stations.
§
The
Stanford Synchrotron Radiation Laboratory (SSRL)
SPEAR3
Project Completed. The four-year SPEAR3 Upgrade Project, jointly funded
by the Department of Energy and the National Institutes of Health, was completed
on time and within budget (SPEAR stands for the Stanford Positron Electron
Accelerating Ring). The 3-GeV SPEAR3 light source produces x-ray beams having 1
to 2 orders of magnitude higher photon brightness than the SPEAR2 accelerator it
replaced, enabling enhanced scientific capabilities comparable to those of other
third generation light sources.
SPEAR3
Commissioned and Operation for Users Commenced. The
SPEAR3 storage ring was commissioned within a remarkably short time, beginning
with equipment turn-on in mid-November 2003, and ending with the first 100-mA
beam delivery to users in early March 2004. The speedy commissioning enabled the
SSRL user program to begin again only 11 months after the SPEAR2 shutdown.
First
Diffraction Patterns are demonstrated with the SPPS. The
first measurements of diffraction patterns from several prototypical samples
were achieved at the sub-picosecond pulse source (SPPS). The first signals from
the electro-optic pulse length and jitter experiment have been recorded yielding
resolution limited pulse lengths of 1 picosecond. The preliminary jitter results
indicate root-mean-square timing of the order of 250-300 femtoseconds.
Source
of Excessive Beam Emittance Found. Important progress in
understanding the sources of excessive electron beam emittance from a
photo-cathode gun has been made at the SSRL Gun Test Facility, setting the path
for achieving the design goal for the Linac Coherent Light Source (LCLS)
electron gun. The discovery indicates that a time dependent kick significantly
increases the projected beam emittance. Eliminating the beam kick will enable
operation of the high-charge gun with a sufficiently low emittance for x-ray
Free Electron Laser operation at the LCLS.
§
The
Intense Pulsed Neutron Source (IPNS)
IPNS
Instruments Upgraded. The IPNS continues to make major instrument
upgrades to maintain world class science capabilities for its users: 1) more
than one half of the user instruments have migrated to a new data acquisition
system that enables faster and more flexible data binning; 2) installation of
neutron guides and frame definition choppers has boosted flux on sample for some
instruments by 2-20 times; and 3) improved detectors and collimation and larger
detector coverage have significantly reduced the time required to collect
neutron data. Successful commissioning of a new IPNS target from recycled disks
recovered from end-of-life targets has provided a cost effective alternative to
the construction of entirely new IPNS targets and enables IPNS operations for an
additional six years.
IPNS
Hosts the National Neutron and X-Ray Scattering School. During
the two-week period of August 15-29, 2004, Argonne National Laboratory again
hosted the National School on Neutron and X-Ray Scattering. The school continues
to attract outstanding graduate students and post-doctoral appointees with 134
applications for the 60 positions available in 2004.
§
The
Manuel Lujan Jr. Neutron Scattering Center (LANSCE)
Goniometer Installed on
Small-Angle Neutron Scattering Instrument.
The goniometer is able to position the sample in the neutron beam with any
orientation. Thus, it provides for a complete measurement of diffraction space,
giving information on the crystal three-dimensional structure over large length
scales from 1 to about 100 nm. Research problems that will benefit from this new
capability include flux-lattice studies in superconductors, super lattice
structures, and self-assembling colloidal structures.
Spin Echo Spectrometry
Demonstrated. This technique, achieved
for the first time at a pulsed neutron source, has application to diffraction
problems in nanoscale materials systems and was demonstrated on a dilute
solution of 58 nm diameter polystyrene spheres in deuterium oxide.
High-Intensity Powder
Diffractometer (HIPD) Refurbished. The
instrument is now fully operational for studies of atomic and magnetic structure
of crystalline and noncrystalline powders, liquids, phase transitions, small
samples, and absorbing materials. Due to its very high counting rates,
time-resolved measurements are also possible as recently demonstrated in a
diffraction study of the curing process of cement.
§
The
High Flux Isotope Reactor (HFIR)
Operational Milestone Celebrated. On April 21, 2004, HFIR began its 400th
operating cycle in its 38 year history. The length of an operating cycle depends
on the time it takes for the reactor's uranium fuel to become depleted. A
celebration marking this anniversary was held on May 15.
Neutron Scattering Instruments
Upgraded. The upgraded HFIR has
state-of-the-art neutron scattering instruments that are among the world's best.
In FY 2004, the HB-2B Residual Stress Diffractometer was brought into
operation in the HFIR Beam Room. The HB-2D triple-axis monochromator shield was
installed at the end of the HB-2 tunnel, and the Reflectometer and SNS Detector
Station on this beam tube are operational. The WAND diffractometer, one of the
instruments in the US-Japan International Collaboration, will also be
operational, completing an important milestone in the HFIR Upgrade project.
Cold
Source Comprehensive Hazards Analysis Completed. One
of the premier features of the HFIR upgrade will be the addition of an
environment of super-cold liquid hydrogen. This environment literally chills the
neutrons so they have less thermal energy with longer wavelengths, which make
them valuable tools for the study of larger, more complex atomic and molecular
structures. The HFIR Cold Source Comprehensive Hazards Analysis was completed
and submitted to DOE in support of the October 4, 2004 milestone.
Reactor
Equipment Upgraded. New
Instrument Air System compressors, dryers and receivers were installed in FY 2004.
These components replace obsolete equipment and will simplify the system by
reducing the number of valves in the system significantly.
§
The
Combustion Research Facility (CRF)
Sample Preparation Laboratory
Ready for Advanced Microscopy. A
laboratory has been converted to a sample preparation space for the research
activities in the Advanced Microscopy Laboratory. The new lab is equipped with
instrumentation and supplies for preparing ultra-clean samples critical to
single molecule imaging of biomolecules and nanomaterials.
Optically Accessible Engine
Facility Established. The facility’s new
automotive-scale Homogeneous-Charge Compression-Ignition (HCCI) engine provides
versatile optical access, accommodating the study of combustion via a
laser-based investigation of in-cylinder processes. The facility is well suited
for the examination of advanced fuel-air mixture preparation strategies that
have been proposed as a way of achieving the strong potential of HCCI engines.
New Instrument Developed to
Investigate Complex Reaction Processes. A new
instrument consisting of an ion- and laser-beam surface analysis system coupled
to time-of-flight and high-resolution Fourier Transform ion cyclotron resonance
mass spectrometers has been built and tested. The instrument is used to
investigate complex spatiotemporal reaction processes related to the aging of
materials and biological processes at the cellular level.
New Laser Diagnostics Measure
Diesel Particulate Emissions.
Laser-induced incandescence (LII) and Laser-Induced Desorption with Elastic
Laser Scattering (LIDELS) are new diagnostic techniques that provide previously
unobtainable time-resolved measurements critical for the optimization of engine
performance. Real-time measurements are particularly crucial for the development
of regeneration strategies for lean NOx catalysts and diesel
particulate filters.
Selected FY 2003 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
Towards
an Exciton Condensate – A New Form of Matter.
A
Bose-Einstein condensate, a form of matter heretofore observed only in atoms
chilled to less than a millionth of a degree above absolute zero, may now have
been observed at temperatures in excess of one Kelvin in excitons, the bound
pairs of electrons and holes that enable semiconductors to function as
electronic devices. Researchers have
observed excitons in a macroscopically ordered electronic state, indicating the
formation of a condensate. The
observations were made by shining laser light on specially designed nano-sized
structures called quantum wells, which were grown at the interface between two
semiconductors – gallium arsenide and aluminum gallium arsenide.
These quantum wells allow electrons and electron holes (spaces in the
crystal that are positively charged) to move freely through the two dimensions
parallel to the quantum well plane, but not through the perpendicular dimension.
Under photoluminescence, the macroscopically ordered exciton state
appeared against a black background as a bright ring that had been fragmented
into a chain of circular spots extending out to one millimeter in circumference.
Just as the Nobel prize-winning creation of Bose-Einstein condensate
atoms offered scientists a new look into the hidden world of quantum mechanics,
so, too, will the creation of Bose-Einstein condensate excitons provide
scientists with new possibilities for observing and manipulating quantum
mechanical properties. The
observation also holds potential for ultrafast digital logic elements and
quantum computing devices.
Magnetic
Nanocomposites: The Next Little
Thing.
Magnetic materials are indispensable
to a modern industrial society; however, it is no longer possible to squeeze
significantly better performance out of today’s most advanced magnets.
A new approach is to create a composite material of two magnetic
materials combined on the nanoscale to create a material with better performance
than either taken separately. The
boundary between the two magnetic materials is exceedingly important.
Studies of bilayers of magnetically-hard and magnetically-soft magnetic
materials have revealed that diffusion between the two materials alters the
interface between them, resulting in improved magnetic properties.
Theoretical modeling confirms that interfacial modification can enhance
interlayer magnetic coupling. The
results reveal the potential of careful interfacial control for improving
magnets through manipulation of the material at the nanoscale.
Tuning
the Properties of Materials at the Nanoscale.
As the size of silicon electronic devices shrinks toward the nanometer
scale, the properties of the nanometer-thick silicon thin film in the devices
depart from those of the bulk form of silicon.
Nanostressors will be able to tune the properties of such thin films.
For example, germanium islands grown on silicon act as nanostressors to
shape the silicon film. The induced
bending of the silicon film modifies the local electronic and optical properties
of silicon. This ability to
“tune” the properties of solid thin films is expected to become more
prominent as semiconductor devices shrink to ever smaller scales.
New
Nanoscale Structures Form where Grain Boundaries Meet Surfaces.
A newly discovered nanoscale “defect” may be connected to unusual
behavior of metal catalysts and thin films, which are critical to the chemical
and electronic industries. A
distinct channel with a V-shaped cross section has been observed along the
intersection of a grain boundary with an external surface.
Atomic-resolution observations of gold surfaces in combination with
atomic-scale simulations show that this channel has a different crystal
structure than the remainder of the material.
One implication is that when the grains become sufficiently small, these
channel regions may dominate the surface and result in very different reactivity
and catalytic activity than expected based on the bulk structure.
These channel defects may also pin grain boundaries, slowing or
preventing their motion and affecting the processing of thin films for
microelectronics. Furthermore, the
channels can be thought of as naturally occurring nanoscale wires along the
surface of a material, whose arrangement could be controlled by appropriate
processing.
Imaging
Single, Individual Molecules.
By using a tightly focused beam of electrons less than a nanometer in
diameter and by reconstructing images from the electron scattering data, the
exact atomic positions in an individual carbon nanotube have been determined.
Images of high resolution and high contrast can be obtained as has been
shown by solving the structure of a single, double-walled carbon nanotube – a
very complicated problem involving one tube nested in another.
The technique has the potential to allow imaging of atomic arrangements
in individual non-periodic structures such as biological macromolecules.
Nanofluids
Improve Heat Transfer.
Suspensions of nanoscale metal
particles or carbon nanotubes in fluids exhibit unusual enhancements in thermal
conductivity. Picosecond
measurements using laser techniques have been used to make the first
quantitative measurements of heat transfer at the solid/fluid interface.
Very large improvements for thermal conductivity are expected based on
simple theory for carbon-nanotubes, but are not observed.
The picosecond data shows that the thermal coupling between the nanotube
and the surrounding matrix is weak, greatly impeding heat transfer in the
carbon-nanotube composite. The
results also indicate that the thermal conductance at the particle/fluid
interface is highly sensitive to both structure and chemistry.
Silicon:
From Information Age to an Efficient Light Emitter?
Silicon is the bedrock on which the information age is built, but it is a
notoriously poor light emitter. The
holy grail of silicon technology is to make silicon an efficient light emitter
so that digital information can be converted to light for the ultimate
transmission speed across optical fiber networks.
New calculations have shown that a novel impurity superlattice structure
of thin-layer oxide could do precisely that by altering silicon electronic
charge characteristics to couple directly to light.
This breakthrough opens the door so that the light-emitting efficiency of
silicon could be drastically enhanced. This
discovery will dramatically impact the microelectronics industry by
significantly reducing the cost and complexity associated with the integration
of optoelectronics into silicon-chip products.
Synchrotron
Light Sources Help Reveal Secrets of Welding.
Welding is a critical metal joining
technology used worldwide in the energy, automotive, aerospace, construction,
and chemicals industries. Rapid
cooling during welding induces numerous phase changes in the metal.
Theories have been developed to describe this, but they have never been
verified experimentally. Time-resolved
x-ray diffraction using synchrotron radiation has now been used for the first
time to monitor in-situ phase evolution of a multi-component steel weld during
melting and subsequent solidification. The results show that equilibrium
theories applied to rapid cooling conditions are not valid for steel welds
containing fast diffusing (carbon) and slow diffusing (aluminum) atoms.
This new ability to observe the competition of multi-component phases at
the microstructural level will make it possible to design stronger and tougher
welds, chemically tailored for optimum performance.
Ultrathin,
Laminar Films for Instantaneous Computer Boot-up. A
new technique has been developed to deposit metal atoms onto thin oxide layers.
This technique will help next-generation computers boot up instantly by
making entire memories immediately available for use.
The method anchors ultrathin metallic cobalt layers on sapphire by using
a surface chemical reaction that overcomes an island formation problem that has
long plagued researchers. The new,
inexpensive trick to prevent island formation is as simple as exposing thin
oxide films to water vapor before depositing the metal layer.
The thin metal layer achieves crystallinity after the deposition of only
a few atomic layers. This process
should be applicable to a wide range of metals
on metal oxides.
Novel
Synthesis of Shape-Controlled Nanostructures.
Fabricating shape-controlled
nanostructures such as nanowires and nanodots plays a central role in nanoscale
science and technology. A novel
electrodeposition process has been developed to self-assemble an array of
nanostructures on flat surfaces. The
new technique is based on the application of an electric field to ions on
graphite substrates immersed in an aqueous solution.
A large variety of voltage-controlled nanostructures have been grown such
as cubes, pyramids, pentagons, hexagons, nanowires and snowflakes in
superconductors and ferromagnets as well as in emerging application systems such
as catalytic silver and hydrogen-sensing palladium.
These unique nanostructures provide a new theater to explore shape
effects on quantum confinement and present new opportunities for nanoelectronic
applications.
Biomolecular
Route
to Photovoltaic and Semiconductor
Nanocrystals.
Biology exhibits a remarkable
ability to control the nanostructures of materials, such as the exquisitely
shaped microscopic shells of diatoms and radiolarians, with a precision that far
exceeds the capability of present human engineering.
Now, the biomolecular mechanism that directs the nanofabrication of
silica in living organisms has been harnessed to direct the synthesis of
photovoltaic and semiconductor nanocrystals of such materials as titanium
dioxide, gallium oxide, and zinc oxide -- materials that biology has never used
in structures before. Proteins from
a marine sponge – and their counterparts produced from cloned, recombinant DNA
– were used to catalyze and structurally direct the growth of the inorganic
semiconductors at low temperature and under mild conditions, in marked contrast
to the need for elevated temperatures and caustic chemicals presently required
by conventional manufacturing methods. The
nanocrystallites of gallium oxide formed in this process show a preferential
alignment directed by the underlying proteins, revealing a template-like
structure-directing activity of the biomolecules.
Furthermore, the proteins working at low temperature produce and
stabilize crystal forms of gallium oxide and titanium dioxide normally seen only
at very high temperatures. Such
biomolecular routes may lead to new, environmentally benign routes to
semiconductor and photovoltaic materials with improved control over both
nanostructure and performance, as well as improved interfaces between
optoelectronic devices and living systems.
The
Impact of a Single Atom.
Never before has it been
possible to identify single atoms within bulk materials and determine the
influence of a single atom on its surroundings.
Isolated atoms can significantly modify the physical properties of many
of the technologically most relevant and scientifically interesting materials.
While it has long been known that in semiconductors, for example, the
presence of a single dopant atom among 1019 host elements drastically
modifies the macroscopic properties, the possibility of identifying, localizing,
and even measuring the electronic properties of single atoms becomes of
fundamental importance in the nanotechnology era.
We now have that capability. The
aberration-corrected scanning transmission electron microscope allows not only
the imaging of individual atoms inside a crystal, but their chemical
identification. This remarkable
improvement in sensitivity reaches the quantum limit of information, the ability
to probe the electronic environment of a single atom.
Molecular
Cages under Pressure.
The isolation, removal, and
entombment of radioactive waste are challenging scientific problems.
Structural data from high-pressure x-ray powder diffraction has
demonstrated that cage-like zeolites can potentially separate toxic waste from
the environment. Using reversible
superhydration -- the selective absorption of excess water under pressure into
fully hydrated zeolites — the immobilization of commonly occurring
radioisotopes such as 90Sr, 137Cs and 60Co via
a “trap-door mechanism” may be realized.
By exchanging ions at high pressures, the holes of the zeolites will
expand due to the excess water entering the zeolite cages.
After pressure release these holes contract again, essentially closing
the trap door and sealing the waste inside the zeolite for good.
Biocompatible
Lasers for Ultrasensitive Detection.
A highly sensitive quantum optics device using a biocompatible
semiconductor laser microcavity has been devised that can analyze and
characterize spore simulants. This
device is based on recent advances in the surface chemistry of semiconductors
and the concept of quantum squeezing of light emitted through a spore flowing at
high speed in the laser’s microcavity. This
light squeezing enables even tiny spores to generate a very large signal which,
when analyzed, yields critical biological information including the spore’s
protein coat morphology, shape, intracellular granularity, protein density, and
uniformity. This field-deployable
biolaser should be able to identify different types of spores (for example,
anthrax) within a large population of harmless spores rapidly and effectively.
Electrocatalyst Design for Fuel Cells.
Electrocatalytic
fuel cells at ambient temperature require materials with high catalytic activity
and high tolerance to poisons such as carbon monoxide and sulfur.
The use of alloys presents inherent limitations including a random
distribution of the constituent elements and their propensity to segregate.
The use of ordered intermetallics provides stable ordered phases.
Based on studies of model systems, it is predicted that the ordered
intermetallic bismuth-platinum (BiPt) should exhibit high catalytic activity and
greatly reduced poisoning from carbon monoxide.
These predictions, based on electronic and geometric effects,
respectively, were borne out by experiments.
BiPt catalyzes the oxidation of formic acid is a better material than
pure platinum in some ways; moreover, it exhibits catalytic currents that are
about 30 times those on platinum and is virtually immune to carbon monoxide
poisoning. Although the focus has
been on anode materials, this new design paradigm has clear implications in the
design of cathodes as well as reformer catalysts and could usher a new era in
fuel cell R&D.
Chemical Sciences, Geosciences,
and Energy Biosciences Subprogram
Emergence
from the Primordial Soup.
Fifty years ago, Miller and Urey (Science, 1953) showed that simple
inorganic molecules presumed present in the early earth atmosphere could yield
amino acids after exposure to an electric discharge.
Subsequent models of the chemical origin of life were complicated by the
requirement to explain the asymmetric (chiral) nature of DNA and its components.
Both of these elements are addressed in recent work using advanced mass
spectrometric tools to study amino acid aggregation and reaction products in the
gas phase. The simple amino acid
serine is the commonly accepted product of formaldehyde and glycine, both known
to exist in interstellar space. Using
sonic-spray ionization with mass spectrometric detection, researchers have shown
that certain, especially stable, clusters of serine are homochiral, that is,
exclusively one of the possible symmetries.
Furthermore, in reactions of the cluster with other important biological
molecules, the asymmetry is passed on to the reaction products.
These observations rationalize a model of prebiotic chemistry beginning
with the assembly of homochiral serine octamers.
Following selection of a particular homochiral cluster by an unknown
asymmetric species, reactions with other biologically relevant molecules could
pass on the asymmetry as further chemical reaction led to the formation of
chiral, self replicating, life forms.
Designer
Solvents. Ionic liquids have
already replaced volatile, polluting hydrocarbon solvents in some industrial
processes, and progress is being made in using ionic liquids for inherently safe
processing of nuclear fuel and radioactive waste.
It is important to understand how chemical reaction patterns are
influenced by the unusual environment of ionic liquids.
New studies have explored fast reactions in ionic liquids by pulse
radiolysis and have shown that charged species, such as a bare electron
surrounded by solvent, move more slowly in ionic liquids in comparison to
neutral species, just the opposite of what is seen in normal solvents.
Also discovered was a reactive and highly mobile form of the electron
that exists for only a few trillionths of a second in normal solvents but
persists thousands of times longer in ionic liquids.
Reactivity
within Nanovessels. The
elusive challenge of attaining chemical selectivity close to 100 percent for
reactions in aqueous solution may eventually be achieved by mimicking Nature’s
most selective catalysts – enzymes.
Researchers are attempting just that by synthesizing stable and
semi-rigid inorganic cage structures that are able to sequester organometallic
catalysts in their interior. By
using the restrictive environment of the nanovessel cavity, they have shown
reactant-selective organic transformations.
As a dramatic demonstration of reactant selectivity, they have shown that
these encapsulated complexes react with aldehydes with rates that depend on the
size of the molecule, unlike the same complexes in solution, which cannot
discriminate among aldehydes of different length.
Fundamental
Studies of Water. It is
difficult to identify a quantity more fundamental to chemistry than the O–H
bond dissociation energy of water. Its
importance arises from its ubiquity, which ranges from elementary reactions to
those in complex environments such as flame chemistry or atmosphere chemistry.
A joint experimental/ theoretical study recently revised the value of
this bond dissociation energy by a small amount.
Although a relatively small change, the impact of this correction is
enormous. It will cause changes in
the gas-phase acidity of water, several proton affinities, all R-OH bond
dissociation energies, reaction enthalpies of all OH reactions, and heats of
formation computed relative to H2O or OH bond dissociation energies.
Storing
Energy in Dendrimer Trees. Dendrimers
are nanoscale molecules constructed from branches connected to a central core.
If a dendrimer is built with an electron acceptor in the core and
electron donors on the branches, the molecule can capture and temporarily store
energy from light by moving electrons from the branches to the core.
Further chemistry can then be used to capture the energy permanently
before it is dissipated by electron transfer back to the branches.
A dendrimeric system has been designed that functions as an electron
antenna, absorbing several photons to create a core with a long lifetime.
The stored energy can be lost if the electron returns to the “hole”
it left behind. However, for
dendrimers with branches long enough to allow their tips to touch, the holes are
trapped on pairs of molecules at the tips, and the charge-separated state lasts
for a long period of time.
Coherent
Surface Plasmons in Nanoscale Systems. One of the great promises
of nanotechnology is the localization of phenomena on the nanoscale.
Theoreticians have recently described the nanoscale analog of a laser in
which coherent optical-frequency radiation fields are confined and amplified in
nanosystems. They show that quantum
generation of surface plasmons for a nanoscale v-shaped metal or semiconductor
pattern can lead to stimulated emission and gain for certain highly localized
plasmon modes. Such a device has
been christened a SPASER, for Surface Plasmon Amplification by Stimulated
Emission of Radiation. If realized,
the SPASER has enormous potential applications in nanotechnology, including
optical detection and information processing.
Triple-Action
Catalytic Polymerization. Catalysts
that involve multiple functions working in concert at the molecular level offer
dramatic advantages over single-function catalysts by reducing intermediate
separation steps and achieving unusual reaction selectivity by controlling the
competitive interplay of catalytic sites and the various molecular species
present in the solution. Triple
functions were synthesized on a complex catalytic compound that is active for
ethylene polymerization. The
terfunctional catalyst produces branched polyethylene with regular structures
that cannot be obtained with a single catalyst or a pair of catalysts working in
tandem. The extent and type of
branching exhibited by the polymers, and therefore the chemical, mechanical, and
optical properties of those materials, can be controlled by adjusting the ratios
of the different functionalities.
Multidimensional
Chemical Analysis of Attomole Sample.
Modern applications of chemical analysis, ranging from pollution studies
to homeland security, increasingly require the ability to interrogate extremely
small sample sizes. These
mass-limited situations might arise because the sample is incredibly expensive,
unusually toxic (biothreat agents), or inherently difficult to obtain in large
quantities (intracellular signaling molecules).
Conventional instrumentation is challenged, because their requirement for
large sample volumes leads to extremely diluted samples.
Researchers are developing solutions to this conundrum by exploiting the
special electrokinetic flow properties of tiny cylindrical capillaries to create
multilayer chemical instrumentation capable of addressing samples as small as
1,000,000 molecules and below. Because
the capillaries are less than 100 nanometers in diameter, they can control fluid
flow among layers of microchannels, thereby making it possible to sequentially
link separate chemical manipulations. For
example, scientists recently demonstrated the use of a nanocapillary molecular
gate to detect and capture a 100 attomole (10-16 moles) band from a
chip-based electrophoretic separation, establishing a new low for preparative
chromatography of mass-limited samples.
DNA Transport through a Single Carbon Nanotube.
Carbon nanotubes have been proposed as useful media for a variety of
applications such as hydrogen storage, chemical separation, and ultrasensitive
sensors. A common research theme
among these applications is the need to understand mass transport through such
nanoporous materials. In a dramatic
demonstration of its separations capability, a single, multiwalled carbon
nanotube has been immobilized within an electrophoretic membrane test chamber
and the passage of single DNA molecules has been monitored by fluorescence
microscopy. Individual DNA molecules
having a diameter smaller than the nanotube’s opening were observed to readily
pass through, whereas larger DNA molecules exhibited behavior consistent with
trapping and hindered passage. Because
of the simple structure of the nanotubes, modeling can yield insight into the
mass transport properties of its very small pores.
Actinide
Supramolecular Chemistry: Giant Rings for Heaviest Atoms.
Supramolecular chemistry is the controlled formation of large molecular
aggregates from smaller subunits. The
formation is controlled in order to achieve or optimize specific chemical
properties. Actinide ions, the
largest metal ions, have unique electrons configurations and represent materials
that can be extremely useful or extremely dangerous.
Supramolecular assemblies called helicates have been created where six
thorium ions are encapsulated in a “box” (cluster) that self-assembles from
eight smaller assemblies, which will now be investigated for their ability to
remove toxic ions such as the actinides from the body.
Targeted Recognition of Actinide Ions.
Fundamental research on the selective complexation of specific ions of
radioactive elements with disk-like complexants has led to simple and sensitive
detection of these ions. Several
classes of disk-like complexants create strong bonds between actinide ions, all
of which are radioactive, and nitrogen atoms in the cages.
These bonds cause transitions in electronic and vibrational spectra that
result in visible color changes that occur only when specific actinide ions, in
particular ions of neptunium and plutonium, are present.
These colored complexes are important because of the changes they cause
in electronic and vibrational structure and because they represent opportunities
for detection of potentially hazardous radioactive ions that could be released
into the environment – or to reassure first-line responders and the public
that such species have not been released.
Life Cycle of a Water Molecule on an Electrode.
Technological progress towards a future hydrogen economy relies on
understanding molecular-level phenomena governing conversion hydrogen formation
at the electrodes in electrolyzers and fuel cells.
Ruthenium dioxide is unsurpassed at enhancing catalytic activities in
room-temperature fuel cell anodes, and it is a very promising electrocatalyst.
Using synchrotron x-ray studies, fascinating sequential rearrangements of
surface water molecules were discovered, evolving from a loose hydrogen-bonded
water layer, to a hydroxide layer, and to a dense form of water, which exist on
the ruthenium dioxide surface at different applied potentials. These interfacial
forms of water may be the intermediates long suspected to be responsible for
promoting oxidation of hydrogen and methanol in the fuel-cell environment as
well as promoting the oxygen-evolution reaction.
These previously unavailable molecular-level details of the
energy-conversion processes provide scientific impetus for a more rational
design of high performance electrocatalysts.
This first-of-its-kind study was possible because of the unprecedented
level of sensitivity afforded by the high brilliance of today’s synchrotron
radiation light sources.
Identification and Structural Determination of a Novel Protein Motif.
The protein machinery within a biological cell is manufactured via a
complex assembly line that stretches from decoding DNA into RNA and translating
the message into a polypeptide chain. Subsequent
assembly into larger complexes and covalent linkage of the peptide chain with
other carbohydrate or lipid components may also occur to provide additional
chemical reactivity or specificity. The
photosynthetic machinery that captures light energy and turns it into chemical
energy is assembled in just such a fashion, with both large and small subunits
of the carbon-fixing enzyme, Rubisco, undergoing methylation on lysine residues.
A novel protein motif called the SET domain that carries out the
methylation of Rubisco has been identified and its structure determined.
The SET domain has been found in many other enzymes in a variety of
biological contexts ranging from enzyme substrate recognition to scaffolding and
stabilizing DNA. The common function
of recognizing a molecular structure for subsequent covalent modification may
lead to a common code for deciphering regulatory mechanisms of catalysis and
molecular recognition.
First measurement of how much energy is required to insert a single new protein into a chloroplast.
The presence of internal organelles within the plant cell poses numerous challenges for the coordinated synthesis and trafficking of new proteins, which often must be synthesized in one part of the cell and directed to another sub-cellular compartment. The latter process necessitates the movement of the new protein across one or more membranes. Plant chloroplasts represent a unique opportunity to study the energetics of a mixed transport system that incorporates the cellular challenges of both eukaryotes and microbes. The energetic cost of this process is a fundamental unanswered question in plant biology, since the majority of photosynthetic apparatus proteins are continuously synthesized and imported into the chloroplast, then rapidly degraded. DOE/BES support has led to the first measurement of how much energy is required to insert a single new protein—an astonishingly high proton flux that is equivalent to the energy stored within 10,000 ATP molecules! Thus approximately 3% of the total energy output of the chloroplast from photosynthesis is devoted to maintaining the photosynthetic machinery. This knowledge provides the foundation for future strategies for more efficient light-harvesting applications for renewable energy.
Selected FY 2003 Facilities Accomplishments
The
Advanced Light Source (ALS)
Record
Low Vertical Emittance Demonstrated. The
emittance is a key parameter that describes the circulating particle beam in a
storage ring. Accelerator scientists
have reduced the ALS vertical emittance to 5 picometer-radians during
accelerator physics experiments. This
is the lowest emittance value ever realized in any storage ring. While this
emittance is a factor of 20 lower than the value normally used in ALS operation
for users, it will be especially important for future spectroscopy studies in
which the highest possible resolution is important.
Femtosecond
R&D Program Launched. The study of ultrafast dynamical processes on
the time scale of fundamental processes, such as a molecular vibration, is one
of the most active areas of modern science. An
ALS R&D program was initiated that aims to produce ultrafast x-ray pulses by
means of a technique known as electron-beam slicing. To
generate x-rays from soft to hard x-ray energies with the maximum intensity
the first, narrow-gap, in-vacuum undulator
will be installed in the ALS.
Beamline
Devoted to Study of Soft X-Ray Coherent Science. Exploitation of the coherence of
undulator light has not kept pace with that of other properties, such as
brightness. To address this issue at
the ALS, a branchline dedicated to coherence has been added to an existing
undulator beamline that will produce microwatts of tunable coherent soft x rays.
This new capability will allow users to carry out a wide range of experiments in
both scattering and fundamental optics.
Next-Generation
Detector for Synchrotron Radiation Developed. The brightness of third-generation
synchrotron radiation sources often generates huge signal rates that overwhelm
the capabilities of existing detector systems. Often,
the detector saturation problem both prevents the fullest utilization of the
synchrotron light and limits the realization of certain new types of
experiments. To overcome this bottleneck, the ALS has developed and successfully
tested a high speed (more than 1 GHz), next-generation detector based on
high-energy physics technology.
The Advanced Photon Source
(APS)
A Bull’s Eye for Storage Ring
Beam Orbit Stability. Stable x-ray beams are critical for all users of
x-ray facilities, particularly those users who microfocus x-rays onto small
samples. X-ray beam-position monitors developed for the APS insertion device
beamlines are providing beam stability that is now equivalent to firing a stream
of bullets through the bull’s eye of a target from several miles away.
New
Information from APS Could Lead to Improved Data Storage. A surface twisted magnetic state
predicted 15 years ago has, for the first time, been confirmed using a new
experimental technique at the Basic Energy Sciences-funded X-ray Operation and
Research sector 4 at the APS. Twisted magnetic states of materials have
important ramifications for applications in the development of improved magnetic
memory.
EPICS
Collaboration Helps APS and the World. EPICS (Experimental Physics and
Industrial Control System) software developed at two U.S. Department of Energy
national laboratories is being used worldwide to control complex mechanical
systems, from accelerators that reveal the nature of subatomic particles, to
observatory telescopes that view distant galaxies, to industrial control
processes such as semiconductor wafer manufacturing.
Optics
Capabilities at the APS Enable New Dynamical Studies of Liquids and Solids. Inelastic x-ray scattering (IXS)
is a synchrotron x-ray tool that opens new vistas for the study of
high-temperature materials. The x-ray optics capabilities of the APS have
reached a level that makes possible implementation of an IXS spectrometer with
exceptional resolving power.
A
Breath of Fresh Air for Insect Physiology. A
technique that couples phase-enhanced x-ray imaging to the intensity of APS
x-ray beams has revealed a previously unknown insect breathing mechanism.
Further development of this technique could have important implications for
human health care and afford the potential for a wide variety of other
materials-related applications, including
detecting and studying cracks, voids, and other boundaries inside optically
opaque structures; studying fluid flow in rocks and soils for oil exploration
and recovery; and characterizing advanced materials, such as ceramics and fiber
composites.
The National Synchrotron
Light Source (NSLS)
High
Gain Harmonic Generation (HGHG) FEL Reaches Saturation in Ultraviolet. The NSLS is pioneering the
development of laser seeded Free Electron Lasers (FEL). The
HGHG FEL makes uses of a Ti-Sapphire seed laser to produce fully coherent 266 nm
light. This marks the first HGHG FEL to successfully reach saturation in the
ultraviolet regime and thereby obtaining sub picosecond pulses with energy in
excess of 100 microjoules.
New
Powder and Single
Crystal
Diffraction Beamline Completed. A
new bending magnet beamline, X6B, has been completed.
The beamline was constructed to meet the increasing demand of nanoscience
users for powder and single crystal x-ray diffraction.
The beamline consists of a Si(111) monochromator, tunable from 5 keV to
20 keV, and a double focusing mirror. The
beamline is designed to perform (a) time-resolved powder diffraction, (b)
combined x-ray spectroscopy and x-ray diffraction, (c) single crystal
diffraction, and (d) measurement of electron density of excited states.
Superconducting
Wiggler Beamline Upgraded. The
X17 superconducting wiggler beamline is the only high-energy x-ray insertion
device at the NSLS. It serves a
large and very productive earth science and high-pressure users community.
In FY 2003, two new experimental hutches were constructed so that a
materials science instrument, a large volume press instrument and a diamond
anvil cell instrument will each have a dedicated experimental hutch.
All three programs will be able to operate simultaneously, thus
significantly increasing the amount of beam time available to these user
communities.
Low-Energy
X-Ray Beamline Upgraded. The
low-energy x-ray region is important because it covers the K absorption edges of
Si, S, P, Cl, and L edges of 4d transition metals.
X-ray spectroscopy and x-ray resonant scattering in this energy range are
valuable tools in catalysis, environmental science, magnetism and bio-materials.
A new monochromator was designed and installed in FY 2003 to improve the
cooling of the monochromator crystals in X19A beamline.
The new design has led to better energy and intensity stability of the
beamline.
The Stanford Synchrotron
Radiation Laboratory (SSRL)
First
Beam from the Sub-Picosecond Pulse Source (SPPS) is Achieved. Ultrafast
pulses of x-rays are key tools for probing the electronic and structural changes
in materials during fast chemical reactions and phase changes.
To this end, the SPPS was installed in the SLAC Final Focus Test Beam
Facility, which generates pulses of 8-10 keV x-rays with 107
photons/pulse at a pulse rate of 10 pulses per second.
The peak brightness of these x-ray pulses exceeds that of any existing
x-ray source. The SPPS is planned to
operate 3-4 months per year through 2005, when it will be displaced by the
construction of the Linac Coherent Light Source, a much more intense source of
short x-ray pulses.
SSRL’s
Final Run with SPEAR2 Ends on a Perfect Note.
SSRL’s
most recent experimental run prior to the decommissioning of SPEAR2 ended very
successfully with SPEAR delivery of scheduled beam time to users at the 100%
mark during the last week of operations. Even though the FY2003 run was shortened by about 4
months due to the beginning of the SPEAR3 installation, a total of 813 users
came to SSRL during the run to conduct experiments on 32 stations.
The up time average for the entire FY2003 run was 96.8%.
SPEAR3
Installation Program Proceeding on Schedule.
The
SPEAR3 Installation Program began on schedule on March 31, 2003. The
Installation Program involves three phases: demolition
of SPEAR2, modification of the facilities to meet SPEAR3 needs, and finally the
actual installation of SPEAR3 technical systems and components. Each phase is a
complex procedure that is planned in great detail with overall completion by the
end of October 2003.
New
Experimental Station Developed on BL11. A
new experimental station that will be used for both materials scattering and
macromolecular crystallography has been commissioned on BL11.
This new station will help relieve the significant over subscription on
BL7-2 for users performing x-ray structural studies of thin films as well as
provide for single- or multi-wavelength anomalous dispersion (SAD and MAD)
experiments to be carried out at the Se edge for macromolecular crystallography
applications.
The Intense Pulsed Neutron
Source (IPNS)
Upgrades
of IPNS Instruments Continue. IPNS
continues to make major instrument upgrades and source improvements to maintain
world class science capabilities for U.S. users:
1) an upgrade project for a powder diffractometer, GPPD, has been
completed putting the instrument on a par with the fastest powder instruments in
the world; 2) installation of a guide on QENS, a quasi-elastic spectrometer
boosted flux on sample by a factor of five; 3) redesigning the
moderator/reflector assembly resulted in a gain of 60% neutrons-on-sample for
small angle scattering applications.
Outstanding
Operations at IPNS Continues. For the sixth consecutive year, the IPNS has
exceeded its goal of offering at least 95% reliable operations, achieving a
figure of 97% in FY 2002. This
reliability assures users that experiments can be performed as planned and
offers additional evidence that pulsed neutron sources can be run in a reliable
manner.
IPNS
Hosts the National Neutron and
X-Ray
Scattering
School
. During the two-week period of August 10-24, 2003,
Argonne National Laboratory again hosted the National School on Neutron and
X-Ray Scattering. The school
continues to attract outstanding graduate students and post-doctoral appointees
with 143 applications for the 60 positions available in 2003.
The Manuel Lujan Jr. Neutron
Scattering
Center
at the Los Alamos
Neutron
Science
Center
(LANSCE)
First Results with the 11-T Magnet
at
Lujan
Center
.
The
newly commissioned 11-T superconducting magnet provided Lujan Center users with
the first results of an intensity image (reflection) of neutron data collected
from an antiferromagnetic material on the new Asterix instrument. Significantly,
the mass of material contributing to the reflection is only about 100
micrograms. Moreover, exceedingly
good thermal stability was achieved during the measurements.
Upgraded NPDF Produces 300 Data
Sets. The
Neutron Powder Diffractometer (NPDF) opened its shutter for the first time and
produced over 300 experimental data sets during the run cycle. Promising
results obtained during the run cycle not only put NPDF at the cutting edge of
local-structure determination but also served as a development platform for a
new structure-analysis tool based on pair-distribution functions in disordered
and nanostructured materials.
Upgrades to SPEAR Improve
Reflectivity Measurements. Upgrades to SPEAR have simplified the operation of
the instrument and provided more precise and reproducible reflectivity
measurements. SPEAR is a time-of-flight neutron spectrometer ideally suited to
study thin organic and inorganic layers in a variety of environments. A
recent experiment on SPEAR provided fundamental information about the stability
of model biomembranes in the presence of large electric fields.
Upgrades to LQD Enables More
Sophisticated Small-Angle Scattering Experiments. Small-angle
scattering has been improved at the Lujan Center to keep apace with the
significantly increased cold-neutron flux available to LQD (Low-Q
Diffractometer), which has been increased by approximately a factor of five. These
upgrades will allow more measurements, higher-quality data, and the ability to
perform more sophisticated experiments.
The
High Flux Isotope Reactor (HFIR)
World-Class Triple-Axis
Spectrometers Installed at HFIR. These spectrometers, designated HB-1, HB-1A, and
HB-3, are exceeding performance goals and are equal to the highest intensity
instruments of their kind in the world. The installation of three additional
world-class instruments is under way at the HB-2 shielding tunnel, which was
completed in March 2003. The first
of the new instruments should be available in early fall 2003 with the other two
to follow by the end of 2003.
Shield Tunnel Installed for the
HFIR HB-2 Neutron Beam. The tunnel extends the neutron beam into the beam
room and provides full neutron beam access to four instruments with individual
instrument shutters. Installation of
the instruments will result in a significant increase in the number of
experiments that can be performed using the HB-2 neutron beam.
Construction of the Small Angle
Neutron Scattering (SANS) Guide Hall Completed. The
high bay guide hall will house the new 40m and 35m SANS instruments and
supporting lab space. It will provide a research environment away from the
reactor building that will be used by numerous facility users for physical and
biological material studies.
The
Combustion Research Facility (CRF)
New Capability Developed for
Three-Dimensional Measurements in Turbulent Flames.
Lasers and digital camera systems for imaging of
laser-induced fluorescence in two intersecting planes were added to existing
systems for line-imaging measurements of temperature and major species in
turbulent flames. The combination
yields information on the magnitude and effects of three-dimensional scalar
dissipation, which is a central quantity in combustion theory and modeling.
Station Established to Generate
Periodically Poled Lithium Niobate (PPLN). A
station has been designed and built to pole lithium niobate at the CRF.
PPLN is a quasi-phase-matched crystal that is significantly more
efficient and tunable than conventional crystals.
Recent major advances in nonlinear optical materials have opened up many
new possibilities for chemical sensing. In
particular, the development of PPLN has sparked the advent of broadly tunable,
compact, highly efficient infrared laser sources.
This
technology could be applied to problems such as medical monitoring or transient
molecule detection.
Selected FY 2002 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
Giant
Magnetoresistance (GMR).
GMR is revolutionizing the magnetic recording and data storage industry by
enabling major increases in data density and ease of read/write processes.
GMR is the term applied to layered magnetic systems that undergo very
large changes in resistance in the presence of a magnetic field.
The origin of GMR and its relationship to layered structure is unknown.
New experiments in which the GMR is measured with current flowing
perpendicular to the layer interfaces have yielded insight into the factors
underlying the effect. Measurements
of the GMR in samples with quantitatively determined interfacial structure,
characterized by microscopy and x-ray scattering, have shown a direct
relationship between the GMR and the interfacial roughness.
Since most GMR-based devices rely on the magnitude of the effect, these
results provide guidance for their optimization by interfacial roughness
tailoring.
Multifunctional
Materials.
For the first time, organic materials that exhibit bistability
simultaneously in three channels – magnetic, optical, and electrical – have
been produced. The new materials
have many interesting properties. In
one state, they are paramagnetic (attracted to a magnetic field), infrared
transparent, and electrically insulating; in the other state, they are
diamagnetic (repelled by both poles of a magnet), infrared opaque, and
electrically conducting. The
switching between the two states is thermally driven, and a switching
temperature just above technologically useful room temperature has been
achieved. These multifunctional
materials have the potential for use in new types of devices for electronics,
computers, and data storage where multiple channels are used for reading,
writing, and transferring information.
For the first time, organic materials that exhibit bistability
simultaneously in three channels – magnetic, optical, and electrical – have
been produced. The new materials
have many interesting properties. In
one state, they are paramagnetic (attracted to a magnetic field), infrared
transparent, and electrically insulating; in the other state, they are
diamagnetic (repelled by both poles of a magnet), infrared opaque, and
electrically conducting. The
switching between the two states is thermally driven, and a switching
temperature just above technologically useful room temperature has been
achieved. These multifunctional
materials have the potential for use in new types of devices for electronics,
computers, and data storage where multiple channels are used for reading,
writing, and transferring information.
For the first time, organic materials that exhibit bistability
simultaneously in three channels – magnetic, optical, and electrical – have
been produced. The new materials
have many interesting properties. In
one state, they are paramagnetic (attracted to a magnetic field), infrared
transparent, and electrically insulating; in the other state, they are
diamagnetic (repelled by both poles of a magnet), infrared opaque, and
electrically conducting. The
switching between the two states is thermally driven, and a switching
temperature just above technologically useful room temperature has been
achieved. These multifunctional
materials have the potential for use in new types of devices for electronics,
computers, and data storage where multiple channels are used for reading,
writing, and transferring information.
Transparent
Electronic Devices.
Rather than ordinary glass, imagine that your window panes at home are a
multi-functional wide band-gap semiconductor device that might serve as: an
energy generator, a microprocessor, a detector, and a light modulator.
The potential of wide-gap semiconductors is enormous, ranging from highly
efficient solid-state light sources and high-density data storage to invisible
monitoring devices for national security. The
key in making this dream a reality is to be able to dope these materials with
impurities to achieve both the n- and p-type mechanisms of electrical
conduction. Achieving p-type doping
had been an insurmountable problem. The
root cause was found to be twofold: the spontaneous formation of native defects
and the low-dopant solubility. Suppression
of the defect formation was achieved by chemical design of the band structure of
the semiconductor oxides. This
approach has led to a family of new p-type transparent conducting materials.
These studies have facilitated the experimental exploration of
transparent electronic device materials.
World’s
Smallest Ultraviolet Nanolasers.
The world’s smallest ultraviolet-emitting lasers, based on
”nanowires” of zinc oxide, have a broad range of potential applications in
fields ranging from photonics – the use of light for superfast data processing
and transmission – to the so-called “lab on a chip” technology in which a
microchip equipped with nano-sized light sources and sensors performs instant
and detailed analyses for chemistry, biology, and medical studies.
The nanolasers were fabricated using a new processing method that can
grow arrays of zinc oxide nanowires between 70 and 100 nm in diameter with
adjustable lengths between 2 and 10 microns.
This development continues the progress in semiconductor laser research,
providing new materials that extend the availability of these versatile and
inexpensive light sources from the near infrared and red regions of the spectrum
into the green-blue and near ultraviolet.
Nanotubes
Increase Heat Conduction in Fluids.
Fluids
containing 1 percent carbon nanotubes in oil exhibit a 250 percent increase in
heat conduction. This addition of
nanotubes resulted in the highest thermal conductivity enhancement ever achieved
in a liquid – ten times higher than predicted by existing theories.
This has required the development of new heat conduction models for
solid/liquid suspensions. This
research could lead to a major breakthrough in solid/liquid composites for
numerous engineering applications, such as coolants for automobiles, air
conditioning, and supercomputers.
Fluids
containing 1 percent carbon nanotubes in oil exhibit a 250 percent increase in
heat conduction. This addition of
nanotubes resulted in the highest thermal conductivity enhancement ever achieved
in a liquid – ten times higher than predicted by existing theories.
This has required the development of new heat conduction models for
solid/liquid suspensions. This
research could lead to a major breakthrough in solid/liquid composites for
numerous engineering applications, such as coolants for automobiles, air
conditioning, and supercomputers.
Molecular
Based Spintronic Material.
For years scientists have dreamed of separately controlling the spin and
charge of the electron to create "spin electronics" or spintronics for
next generation electronic devices. We
have advanced one step closer to this goal with the fabrication of a new
molecular solid integrating alternate layers of spin networks with organic metal
networks through crystal engineering. The
close proximity of the spin to the metal – less than one nanometer apart –
promises strong communication of spin and charge while allowing each to be
manipulated separately. The new
material is made by relatively inexpensively using bottom-up self-assembly as
opposed to the elaborate and expensive top-down lithography for other
semiconductor materials.
For years scientists have dreamed of separately controlling the spin and
charge of the electron to create "spin electronics" or spintronics for
next generation electronic devices. We
have advanced one step closer to this goal with the fabrication of a new
molecular solid integrating alternate layers of spin networks with organic metal
networks through crystal engineering. The
close proximity of the spin to the metal – less than one nanometer apart –
promises strong communication of spin and charge while allowing each to be
manipulated separately. The new
material is made by relatively inexpensively using bottom-up self-assembly as
opposed to the elaborate and expensive top-down lithography for other
semiconductor materials.
Deformation
at the Nanoscale.
Large-scale atomic-level simulations reveal how
and why conventional dislocation deformation processes in materials break down
at the nanoscale. Nanostructures can
experience very high internal stress levels; thus, mechanical stability and
compliance represent major obstacles in the development of nanodevices. The
computer simulations demonstrated that, as the grain size becomes ever smaller,
a material becomes harder to deform. However,
at a critical size, dislocations no longer can exist, because they are
comparable to that of the grains themselves, and the material suddenly softens
again due to the onset of novel deformation mechanisms mediated by the grain
boundaries that contain the grains. This “strongest size” was shown to be a
function of not only the material itself but also the stress level to which it
is subjected. These insights will
enable the design of nanodevices with tailored mechanical performance, capable
of withstanding the very high stresses under which they often operate.
Large-scale atomic-level simulations reveal how
and why conventional dislocation deformation processes in materials break down
at the nanoscale. Nanostructures can
experience very high internal stress levels; thus, mechanical stability and
compliance represent major obstacles in the development of nanodevices. The
computer simulations demonstrated that, as the grain size becomes ever smaller,
a material becomes harder to deform. However,
at a critical size, dislocations no longer can exist, because they are
comparable to that of the grains themselves, and the material suddenly softens
again due to the onset of novel deformation mechanisms mediated by the grain
boundaries that contain the grains. This “strongest size” was shown to be a
function of not only the material itself but also the stress level to which it
is subjected. These insights will
enable the design of nanodevices with tailored mechanical performance, capable
of withstanding the very high stresses under which they often operate.
Nano-onions.
Carbon “nano-onions,” generated by carbon-arc discharge in deionized
water, are the latest entry in the fullerene family.
Their structures resemble onions, with a fullerene at the core,
surrounded by multiple layers of fullerene-like carbon.
The arc method produces “nano-onions” with diameters from about 10 to
150 nm. These “Buckyonions” are
easily fractionated on the basis of diameter by using flow field-flow
fractionation, with small particles eluting before larger ones.
Characterization of these “nano-onions” using electron microscopy and
light scattering methods could lead to new and novel applications for these
materials.
Carbon “nano-onions,” generated by carbon-arc discharge in deionized
water, are the latest entry in the fullerene family.
Their structures resemble onions, with a fullerene at the core,
surrounded by multiple layers of fullerene-like carbon.
The arc method produces “nano-onions” with diameters from about 10 to
150 nm. These “Buckyonions” are
easily fractionated on the basis of diameter by using flow field-flow
fractionation, with small particles eluting before larger ones.
Characterization of these “nano-onions” using electron microscopy and
light scattering methods could lead to new and novel applications for these
materials.
A
Trillion Elements per Square Inch.
Magnetic
storage arrays with more than a trillion elements per square inch, ultrahigh
resolution field emission displays, and high resolution, on-chip macromolecular
separations devices have been constructed using a new, patented technique of
self-assembly of polymers. By means
of routine chemical etching processes, large area arrays of nanopores (4-50 nm
in diameter) with very high aspect ratios are produced in a simple, robust
manner. These serve as templates for
pattern transfer to substrates and as scaffolds to direct surface chemistry or
electrochemical deposition of metals for the generation of ultrahigh density,
multilayered nanowire arrays. The simplicity of this technique has a broad
impact across many disciplines ranging from bioactivity to semiconductor
devices.
Molecules
of Gases and Water Swim Upstream.
A theoretical analysis has shown that molecules
of hydrogen, oxygen, and even water can travel across conducting membranes in
opposite directions from what would normally be expected.
An understanding of these membranes is important in the development of
advanced materials systems for energy storage such as fuel cells.
The analysis pertains to a class of materials called perovskites that
can, under some circumstances, conduct charge via both individual electrons and
ionized atoms of hydrogen and oxygen. Individual
chemical species can move in the "wrong" direction from areas where
they are at a lower concentration to areas of higher concentration.
This is normally explained by other driving forces that are taken into
account in a quantity referred to as the chemical potential.
In mixed-conducting membranes, however, the new analysis shows that
neutral (uncharged) molecules can even move contrary to the gradient in the
chemical potential as a result of the simultaneous, coupled transport of
multiple species.
Ultra-Sensitive
Sensors. A new principle for chemical sensors with ultra-high sensitivity has been
developed and successfully demonstrated based on computer simulations of the
structure and properties of particle composites.
These sensors are fabricated by dispersing electrically conducting
magnetic particles into an insulating liquid, then organizing the particles into
chains with a magnetic field while the liquid solidifies by polymerization.
These materials are referred to as Field-Structured Composites.
The particle chains conduct electricity quite well.
When exposed to certain chemical vapors, the polymer absorbs the
chemicals and swells. The chains are stretched ever so slightly to create gaps
between the particles, resulting in conductivity decreases of ten billion or
more. The unprecedented magnitude of
this effect makes these materials sensitive to even trace amounts of vapors.
Inexpensive, portable devices for chemical identification can be achieved
by making an array of sensors, each of which is fabricated with a polymer having
unique chemical affinities, so that any single vapor leaves an identifying
signature on the array.
New
Analysis Method Enables Prediction of Dendritic Pattern Formation.
Just
as water freezes into the elaborate patterns of snowflakes, so do metals form
highly branched patterns called dendrites. These
dendrites control many aspects of the processing and microstructure that
determine alloy properties and hence our ability to use materials.
Dendrite patterns are controlled by minute variations of the interface
between the material and its melt. While
simulations have modeled the atomic processes that occur during solidification,
they have proven inadequate to extract the more subtle information about the
anisotropy. An entirely new method
to extract the anisotropy of energy and mobility from supercomputer simulations
has been devised. The critical step
was the identification of a related quantity that can be calculated with
sufficient precision and then used to simulate dendritic growth.
Additional supercomputer simulations have exploited this new information
to predict the precise nature of dendritic pattern formation in a range of
materials from silicon to nickel.
Superconductors
Show Their Stripes.
Like tigers and zebras, superconductors are distinguished by their
stripes. Some physicists believe
that electricity runs without resistance along “stripes” of electric charge
in these materials. Stripes have now
been observed for the first time the most widely studied of the cuprate
high-temperature superconductors. The
material consists of planes of copper and oxygen atoms located in a square
pattern. Some of the electrons are
missing in these planes leaving positively charged holes that pair together to
produce superconductivity. In a
standard superconductor, these pairs travel through the material without
hindrance producing the perfect conductivity inherent to a superconductor.
However, in the cuprate materials, the copper atoms have a magnetic
moment that makes conductivity in the planes difficult.
Recent neutron scattering measurements made at the High Flux Isotope
Reactor show that the holes form lines or stripes in the superconductor in which
there are no magnetic moments. The
holes can thus move along the stripe in an unimpeded manner.
Like tigers and zebras, superconductors are distinguished by their
stripes. Some physicists believe
that electricity runs without resistance along “stripes” of electric charge
in these materials. Stripes have now
been observed for the first time the most widely studied of the cuprate
high-temperature superconductors. The
material consists of planes of copper and oxygen atoms located in a square
pattern. Some of the electrons are
missing in these planes leaving positively charged holes that pair together to
produce superconductivity. In a
standard superconductor, these pairs travel through the material without
hindrance producing the perfect conductivity inherent to a superconductor.
However, in the cuprate materials, the copper atoms have a magnetic
moment that makes conductivity in the planes difficult.
Recent neutron scattering measurements made at the High Flux Isotope
Reactor show that the holes form lines or stripes in the superconductor in which
there are no magnetic moments. The
holes can thus move along the stripe in an unimpeded manner.
Neutron
Instrumentation for Nanoscience.
Nanoscience requires the study of structures ranging from a
few nanometers to a few microns. A
new neutron scattering technique for study of materials in this size range has
been developed. The method uses the fact that the spin of the neutron has
unique behavior in a magnetic field -- the spin precesses like a top in a
magnetic field so that the total rotation angle of the spin depends on the
time the neutron spends in the magnetic field.
By appropriately designing the magnetic fields, the rotation angle
can be made to depend on the direction of travel of the neutron with
respect to some fixed spatial direction, effectively "coding" the
trajectory angle into the value of the neutrons spin.
This technique can easily be implemented and could be perfected in
time to impact early measurements at the Spallation Neutron Source.
Chemical Sciences, Geosciences,
and Energy Biosciences Subprogram
Catalytic
Chemistry of Gold Nanoparticles. Gold spheres of 2.7 nm
diameter supported on titanium oxide are able to oxidize carbon monoxide, and
spheres of 2.4 nm diameter are able to activate oxygen from air and insert it
into propene readily and very selectively. Yet
bulk gold metal is inert, and particles of slightly smaller or larger diameter
than those cited are also unreactive or unselective.
Using a variety of spectroscopic and chemisorption techniques,
atomic-resolution microscopy, and theoretical electronic structure calculations,
it was shown that decreasing metal particle size provokes changes in the
electronic structures of gold and titanium oxide such that the particles are
able to acquire a partial charge. Those
variations are shown to decrease the binding energy of gold on titanium oxide
(and thus alter the morphology of the clusters), as well as increase the binding
energy of reactants such as oxygen, carbon monoxide, and propene to gold.
The results explain why gold clusters are active and selective oxidation
catalysts and provide a semiquantitative framework to predict catalytic
reactivity on the basis of electronic structure of metal clusters.
New
Nanoporous Catalysts Developed. Nanocrystalline materials
possess unique properties and offer great promise for promoting selected
physical and chemical processes. Crystalline
films of magnesium oxide that consist of tilted arrays of filaments attached to
a flat substrate have been synthesized by impinging a magnesium atom beam in an
oxygen background toward a surface off-normal by 70° to 85°.
The individual filaments are thermally stable, highly ordered and porous,
and contain enormous numbers of binding sites in comparison to a magnesium oxide
flat surface deposited on a substrate. The
high surface area (~1,000 m2/g) and high density of binding sites
potentially render these nanoporous materials extraordinary catalysts.
Multidimensional
Catalyst Arrays. Studies of the affects of particle spacing on the reactivity of catalysts
has been hampered by the inability to produce uniform nanoparticles that are
regularly distributed in a supporting matrix.
Recent work shows that two- and three-dimensional arrays of platinum
nanoparticles are achievable. Two-dimensional
arrays of platinum supported on 4-inch silicon wafers were produced using
electron beam lithography and spacer photolithography.
The latter technique permits variation of particle size from 600 nm to 10
nm. More recently, three-dimensional
arrays of 2-5 nm platinum nanoparticles of vary narrow size distribution were
prepared, and the resulting x-ray and electron diffraction patterns are typical
of crystallinity, hence regularity. The
results significantly enhance enable the production of designer catalysts and
will answer fundamental questions in catalysis.
Nanostructured
Anodes. There is considerable interest in tin/lithium anodes for high-energy
electrochemical storage systems because, in principle, they can deliver
substantially more storage capacity than carbon based lithium ion batteries.
However, the tin-based anode functions by reversibly alloying lithium
into the tin, and a very large volume expansion occurs when lithium is alloyed
(as much as 300 percent). As a
result, the tin based anode system typically has poor cycle life because the
volume expansion and contraction during cycling causes the anode to
self-destruct. New research has
shown that nanostructured tin/lithium anodes prepared via a membrane template
method do not suffer from this loss of cycle life, even after 1,400 charge
discharge cycles. The nanostructured
electrode gives good cycle life because the absolute volume change for a
nanofiber is correspondingly small and because the brush like configuration of
nanofibers provides room to accommodate the volume expansion.
Nanometer-Scale
Faceting of Metals, a Means to Control Reactivity. Bimetallic catalysts are
providing new insights into chemical reactivity.
Upon annealing at elevated temperatures, the atomically rough,
“unstable” surfaces were observed to undergo massive reconstruction at the
nanometer scale, in some instances leading to the formation of surface alloys.
These structural rearrangements were accompanied by corresponding changes
in electronic structure, morphology, and catalytic activity.
Time-dependent, atomically resolved images allowed the measurement of the
rate of facet growth and of their reconstruction in the presence of adsorbates
such as sulfur and oxygen. Catalytic
activity was found to dramatically depend on the composition, structure, size,
and shape of the facets exposed under reaction conditions.
Organic
Semiconductors.
Molecular and polymeric semiconductors are very important organic
compounds that have the potential to replace inorganic semiconductors for
applications in photoelectrochemical and photovoltaic cells for solar energy
conversion of sunlight to electricity and solar fuels (hydrogen, methane, and
alcohols). Photoconversion devices
based on organic semiconductors could be much less expensive and easier to
produce and process because of the present vast technology available for polymer
and molecular processing into continuous thin films and sheets.
Doping the molecular semiconductors to produce the required n-type and
p-type electrical conductivity to create p-n junctions has been problematic as
the dopant has not become part of the molecular or atomic structure of the
compound. Recently, scientists
successfully doped molecular semiconductors and increased the conductivity by
five orders of magnitude.
Long-Lived
Charge Separation in a Novel Artificial Photosynthetic Reaction
Center.
Fullerenes and porphyrins have molecular architectures that are ideally
suited for photochemical conversion and storage of solar energy.
Their use as three-dimensional electron acceptors holds great promise
because of their small reorganization energy in electron transfer reactions that
can significantly improve light-induced charge-separation processes.
Recent research indicated a 24 percent efficient charge-separation within
a molecular tetrad. In this linear
array, a light harvesting antenna assembly composed of two porphyrins and a
fullerene-ferrocene photosynthetic reaction-center mimic were integrated into a
single molecule. The 380 millisecond
lifetime of the spatially-separated and high energy radical pair, a product of
sequential short-range energy and electron transfer reactions, enters a time
domain that has never been achieved in an artificial reaction center.
New
Technique for Detection of Impact Ionization in Semiconductors. The thermodynamic
conversion efficiency with which solar radiant energy can be converted to
electricity or to stored chemical energy in solar-derived fuels is limited by
the energy loss of high energy electrons and positive holes created by the
absorption of high energy solar photons in the photoconversion device.
The thermodynamic efficiency limit can be more than doubled if the high
energy photons can be used to create additional photogenerated current through a
process called impact ionization. For
the first time, scientists have demonstrated a contactless, optical method to
detect impact ionization in semiconductors useful for solar photoconversion.
The method is based on femtosecond time-resolved visible pump-infrared
probe spectroscopy, and can be used to study impact ionization in colloidal
semiconductor quantum dots where electrical contact to the colloidal particles
is not possible. Impact ionization
in semiconductor quantum dots is expected to be greatly enhanced.
Gas-Phase
Chemistry of Actinide Ions.
The studies of gas-phase reactions of ions provide important insights into
fundamental chemistry. Such studies
have previously been limited to transition metal ions and to thorium and uranium
in the actinide series; however, recent work has expanded this approach to the
radioactive actinides, which cannot easily be studied by conventional
techniques. One type of reaction
that has been particularly enlightening involves the metal- or
metal-oxide-catalyzed removal of hydrogen from alkene hydrocarbons.
In these alkene dehydrogenation reactions, the neptunium ion is highly
reactive, the plutonium ion is significantly less reactive, and the americium
ion is essentially unreactive. This
provides clear evidence that the 5f electrons of the actinides beyond neptunium
are inert in these organometallic reactions. Results for the actinide oxide ions
have also been illuminating, revealing a decrease in reactivity between uranium
oxide ions and heavier actinide-oxide ions.
The role of 5f electrons in bonding is central issue in contemporary
actinide science, and these results provide experimental evidence for a change
in the bonding nature of the actinide 5f electrons in molecular compounds,
ranging from being chemically active for the early members of the series to
being inert for the actinides beyond neptunium.
Lattice
Disorder and f-electrons: Evidence For a New
State
of Matter.
An important question is the nature of the non-superconducting
high-temperature superconducting (HTSC) ground state from which
superconductivity arises. Intermetallic
alloys containing f-electron elements, in which superconductivity is
absent or is easily suppressed, allow one to explore this question.
Like HTSCs, f-electron intermetallic alloys often behave as
“non-Fermi liquids” (NFL), so named because they are not consistent with
Fermi liquid theory, which, until recently, has been the basis for explaining
the properties of metals. Of
specific interest is how the atoms surrounding an f-electron atom, and
how disorder in their arrangement, affect magnetic and conducting properties.
A recent study of these arrangements in the NFL compound UCu4Pd
showed that significant lattice disorder exists.
Although such disorder can produce NFL behavior within a Fermi liquid
model, the study showed that there is insufficient disorder for the model to
match the measured magnetic and conductivity data.
That is, the system acts as though it is more disordered than it actually
is. These results strongly imply
that lattice disorder precipitates NFL behavior in this material, perhaps by
amplifying the effect of the disorder, and thereby the possibility of a new type
of metallic ground state.
Cellulose
Biosynthesis. The detection and isolation of cellulose synthase genes is driving new
efforts to understand how cellulose acquires its structural characteristics in
hopes of eventually devising methods of tailoring these characteristics to
facilitate its use as a renewable resource.
Scientists have provided a key piece of information in the biochemical
dissection of the three steps of cellulose synthesis:
1) initiation of the sugar chain; 2) adding sugars to the growing chain;
and 3) stopping the process at a predetermined length.
A single copy of a cellulose synthase gene was introduced into yeast
cells that do not normally make cellulose. The
result was the formation of a specific lipid-sugar compound that serves as a
primer for subsequent chain growth. Understanding
the critical steps in the synthesis of cellulose, the most abundant biomolecule,
will lead to understanding the function of plant cell walls and to engineering
modified renewable resources.
Boron
in Plant Cell Walls.
Research has confirmed the role of the element boron in the growth and
development of plant cell walls. Over
90 percent of a plant’s boron is associated with the cell wall, and boron
deficiency leads to stunted plants with malformed and brittle leaves.
Arabidopsis thaliana mutants with a small change in the structure of a
major type of cell wall carbohydrate show the same characteristics but can be
rescued by feeding with excess borate. This
defect was shown to reduce the plant’s ability to bind the borate that is
needed to form and stabilize the cross-linked cell wall.
Future mechanistic studies relating borate-carbohydrate crosslinking to
physiological growth could lead to improved strategies for the development and
production of renewable biomass resources.
Naturally
Occurring Organochlorine Compounds.
Organochlorine molecules are commonly observed
in natural soils and have been attributed to pollution from manmade sources.
Natural organic matter, such as humic and fulvic acid, in the shallow
subsurface is both universal and little understood.
It has no fixed stoichiometry or structure, cannot be crystallized, and
is famously difficult to characterize reproducibly.
Synchrotron x-ray spectroscopy has been used to document changes in the
chemical state of chlorine in humic materials.
This research confirmed the startling conclusion that natural
organochlorine compounds are common in soil and that there is a net transfer of
chlorine from inorganic to organic forms with common weathering.
Abundant catalytic peroxidase facilitates the chlorination of natural
aromatic organics. These results add
strong support to the hypothesis that chlorination of organic compounds in humic
materials is widespread, and may explain the puzzling organochlorine
concentrations found in otherwise unpolluted environments.
Accurately understanding natural conditions is critical in identifying
and taking action to correct man-made problems.
Quantum
Degenerate Fermi Gases. A new theoretical formulation predicts an unusually high critical
temperature for the onset of superfluidity in a gas of fermionic potassium
atoms. This new form of quantum
matter, which lies between high-temperature superconductors and systems that
undergo Bose-Einstein condensation should soon be achievable experimentally
using optical traps. The ultimate
goal of these experiments is to achieve Cooper pairing, in which pairs of
fermionic atoms “condense” and occupy the lowest quantum states available to
the ensemble of trapped atoms. Such
an accomplishment would permit studies of the underlying mechanism of
superconductivity.
Selected
FY 2002 Facility Accomplishments
The Advanced Light Source
Superbend Magnets Extend Synchrotron Spectral Range.
Originally designed for highest brightness at longer x-ray wavelengths
(soft x rays), the ALS has been retrofitted with superconducting bend magnets
(superbends) that dramatically boost the synchrotron radiation intensity at
shorter x-ray wavelengths (hard x rays) without disrupting the soft x-ray
performance of the existing beamlines, thereby allowing the ALS to service a
broader user community.
Higher-Order-Mode Dampers Increase Storage Ring Stability.
The beam in the ALS storage ring comprises more than 300 discrete
“bunches” of electrons spaced more or less equally around the ring, but
interactions between the bunches can cause the beam to become unstable. Addition
of antennae to the radio-frequency (RF) cavities that power the storage ring has
substantially improved the reliability of the feedback system that combats beam
instabilities.
A New Radio-Frequency (RF) Feedback
Loop
Saves Electrical Power and Money.
Driven by the soaring costs that came with the
California
energy crisis, staff at the ALS found a way to
reduce the electricity bill an estimated 11% by implementing a feedback loop
that reduced power consumption by a klystron power amplifier without interfering
with other RF-cavity controls.
Beamline for Ultrahigh-Resolution Chemical Crystallography Commissioned.
Based on a novel miniaturized design that is
low-cost yet robust and high-performance, the ALS has put into operation a new
beamline that meets the demands of chemists for a tool to rapidly determine the
atomic structure of molecules with sub-angstrom resolution from solid samples
(crystals) as small as a few micrometers on a side.
An Experimental Station Has Been Designed to Study Magnetic
Nanostructures. Consisting of multiple layers of magnetic and
nonmagnetic materials, each only a few atoms thick, magnetic nanostructures are
the foundation for advanced magnetic devices. The new station at the ALS will
allow complete magnetic characterization of each layer separately with x rays
that are polarized in any desired orientation.
The Advanced Photon Source
Operating in
Top-up Mode. One of the principal operational goals has been to run the storage ring in
the “constant current” or top-up mode. Top-up mode consists of injecting a
small amount of charge into the storage ring at regular intervals in order to
maintain a 100 mA current. The major benefit of top-up operation is the virtual
elimination of the beam lifetime (the decay of beam current over time) as a
factor in further improvements or enhancements of the storage ring performance. As
an example, the APS can now operate efficiently with a lower horizontal
emittance, which reduces the source size by a factor of two. This reduction in
size provides a smaller beam spot that can be used to illuminate smaller
samples. Normally, the decrease in
beam lifetime would severely reduce the average current available to the users,
but with top-up, the reduction is non-existent. Top-up operation is now the
standard and comprises 75 percent of the total operating time of the APS. The
APS is the first synchrotron facility to have conceived and implemented top-up
operation.
Canted Undulators for Increased Beamline Capacity.
New technologies devised to offset the ever-increasing demand for
beamline access include the “canted undulator” configuration that produces
two beamlines originating from one point on the ring.
New Information on High-Pressure Fuel Sprays.
An x-ray imaging technique devised at the Basic Energy Sciences-funded
Synchrotron Radiation Instrumentation Collaborative Access Team (SRI-CAT) has
produced unprecedented details of the structure of diesel fuel sprays, including
the first evidence of supersonic shockwaves in sprays as they leave
high-pressure fuel injectors. This information may lead to improvements in fuel
injector-engine emissions and efficiency, and earned a 2002 National Laboratory
Combustion & Emissions Control R&D Award from the Department of Energy.
Nanotomography of Integrated Circuit Interconnects.
A high-resolution scanning transmission x-ray microscope is providing
superior 3-D images of the tiny wire interconnects and other embedded structures
in computer chips without damage to the chips. This unique capability makes it
possible to more easily identify and correct manufacturing problems, and
ultimately to build faster, smaller, more-efficient, and more-reliable
computers.
New Lens for Imaging. An offshoot of APS expertise in x-ray beamline
instrumentation is the first full-scale crystal-diffraction medical-imaging
lens. Resolution with this lens is a factor of three better than with most
current imaging systems. It can be applied to small test animals used by the
pharmaceutical industry and to imaging small parts of the human body. There are
also many possibilities for nonmedical applications, including examination of
nuclear fuel elements and location of radioactive material within a larger mass.
The National Synchrotron Light Source
Source Development Laboratory Laser at 400 nm.
The Deep Ultra-Violet Free Electron Laser (DUV-FEL) facility marked an
important milestone, generating laser light at 400 nm by the process of Self
Amplified Spontaneous Emission (SASE). Achieving
intensity 20,000 times higher than the spontaneous emission, the result showed
that the electron beam and the undulator system can support lasing down to 88
nm, which has strong user interest in the chemical physics community.
Soft X-ray Undulator Beamline Monochromator Upgrade.
A new water-cooled, 6-position interferometrically controlled grating
chamber was installed at beamline X1B. At
present, four new gratings (300, 600,1200, and 1600 lines/mm) covering the soft
x-ray photon energy range from 100eV to 1600eV were outfitted.
Resolving power of more than 10,000 was achieved.
The high energy resolution and extended energy range provided by the new
monochromator will benefit greatly all the experimental programs using the
beamline, including soft x-ray resonant scattering, emission, and imaging.
Ultra-high Vacuum Compatible Soft X-ray Scattering End Station.
A novel resonant soft x-ray scattering instrument has become operational
at the X1B undulator beamline. The
instrument combines the element and electronic state specificity of soft x-ray
spectroscopy with x-ray diffraction, which enables the direct probing of
intrinsic inhomogeneities in strongly correlated electron systems and nanoscale
magnetic systems. For example, the
spatial distribution of the doped holes in an epitaxial film of oxygen-doped La2CuO4+d was determined recently using this instrument
for the first time.
New End Station for Soft X-ray Coherent Scattering and Imaging.
To facilitate nanoscience research, imaging techniques with nanometer
spatial resolution are needed. A new
end station for soft x-ray coherent scattering and imaging was designed and
constructed. It will be used to
develop two and three dimensional diffraction imaging and tomography with tens
of nanometer spatial resolution for nano-magnetic, organic, and biological
systems
The Stanford Synchrotron Radiation Laboratory
Accelerator Modeling Toolbox Developed.
An interactive
accelerator modeling software tool called Accelerator Toolbox has been developed
that greatly increases productivity and flexibility in interactive computer
modeling. By making the Accelerator
Toolbox available to other laboratories via the web, a community of users has
grown who share code and experience in solving similar accelerator modeling
problems.
High Power X-ray Monochromators Deployed.
X-ray
monochromators with high-efficiency crystal cooling utilizing liquid nitrogen
have been designed, fabricated and successfully installed on four high-power
wiggler beam lines. Their enhanced
performance under high heat loads has already resulted in significant
improvements in the stability and throughput of these beam lines.
These monochromators and others to be implemented will be critical
elements in obtaining the ultimate performance available from the SPEAR3
accelerator when it becomes operational in 2004.
Improved Microfocusing System for X-ray Microspectroscopy.
Improved tapered metal capillary focusing optics with a 5 micrometer
focal spot have been successfully integrated into a new system for performing
microspectroscopy measurements. These
developments, which included sample scanning capabilities and software for
mapping the chemical states of the elemental distributions, will ultimately be
propagated to a number of beam lines to enable microspectroscopy research in
biology, materials sciences, and environmental sciences.
Major Progress in SSRL Beamline Upgrade Program.
A beam line upgrade program is underway whose goal is to bring all SSRL
beam lines to optimal performance with SPEAR3 running at 500 mA.
Improvements to date include high-stability mirror systems for the
insertion device-based beam lines, new permanent magnet wigglers, a
high-resolution soft x-ray monochromator, and new liquid nitrogen-cooled
two-crystal x-ray monochromators. Some
upgrades have been completed during the current SPEAR2 operations phase,
bringing higher performance to the ongoing user research programs.
The Intense Pulsed Neutron Source
Upgrades of IPNS Instruments. 1) A project was initiated for the development
of a large-aperture, magnetic bearings-suspension, high-resolution chopper
system for the HRMECS and LRMECS chopper spectrometers at IPNS. 2) A new
scattering chamber for the Small Angle Diffractometer is being installed.
It will improve the data quality and collection rates.
3) Through an IPNS/RIKEN collaboration a neutron compound refractive lens
based on an assembly of MgF2 single-crystal prism elements was tested on the
POSY II beamline for focusing cold neutrons.
Operations at IPNS Continues Outstanding.
For the fifth
consecutive year, IPNS has exceeded its goal of offering at least 95% reliable
operations. This includes delivering
the 7 billionth pulse to the target. This
accomplishment constitutes more pulses delivered to target than any other pulsed
neutron source in the
US
. In
May of 2002, IPNS was designated a Nuclear Historic Landmark by the American
Nuclear Society.
IPNS Hosts the National Neutron and
X-Ray
Scattering
School
.
During the two-week
period of
August 12-23, 2002
, Argonne National Laboratory once again hosted
the
National
School
on Neutron and X-Ray Scattering.
The school continues to attract outstanding graduate students and
post-doctoral appointees with 160 applications for the 60 positions available in
2001.
The Manuel Lujan Jr. Neutron
Scattering
Center
at the Los Alamos
Neutron
Science
Center
Four Instruments
Commissioned. Four world-class neutron scattering instruments completed commissioning
and entered the user program. These
are HIPPO, SMARTS, Protein Crystallography Station, and Asterix.
New data acquisition systems were completed and installed on the new
instruments.
Pharos Rebuilt.
Inelastic chopper spectrometer Pharos enjoyed substantial upgrades,
including detectors on the wide-angle bank, commissioning of the new vacuum
system, new data acquisition electronics and computer system, and a new chopper
control system. Pharos took its
first data and accepted its first users since 1997.
Designed and
Installed New Robust Target System, Mark II.
Using a simplified
Monte Carlo
model, the new target improves
cooling in Mark I moderator and upper target.
A beryllium reflector replaced the lead reflector, cooling was
simplified, and cadmium decoupling in the reflector was removed for more robust
operation. The target received first
beam on
July 8,
2002
, as scheduled.
Completed Basis
for Interim Operation for actinide experiments.
The new authorization basis enabled over a
dozen plutonium and uranium studies to be completed and restores an important
capability to the DOE science complex.
New Shutters and
Interlocks. Greater safety, reliability and performance were achieved by replacement
of Personnel Access Control Systems interlocks on all flight paths, replacement
of all mercury reservoirs and plumbing, and installation of a new fire detection
system. Two new mechanical shutters
and over 300 tons of shielding were installed to enable two new flight paths for
new instruments.
Proton Storage
Ring Instability Tamed. A series of successful Proton Storage Ring development tests confirmed
that the “e-p instability” could be controlled at accumulated charge levels
approaching 10 mC, well above the goal of 6.7mC.
The High Flux Isotope Reactor
Major
Refurbishment of Reactor Vessel Completed. The refurbishment of the pressure vessel's internal components included
replacing the permanent and semipermanent beryllium reflectors and their support
structures. This required maintenance was accomplished without incident and will
support the substantial upgrade in neutron scattering research capabilities at
HFIR.
HFIR Cooling
Tower Replaced. The original 36-year-old wooden cooling tower had significant structural
degradation, required excessive maintenance, and could no longer reliably
support reactor operations. The more efficient replacement tower will cost less
to operate and should last for the remaining life of HFIR.
New Thermal
Neutron Beam Tubes Installed at HFIR. The new beam tubes, which replaced existing tubes that had reached their
end of life, are capable of providing more neutrons to a greater number of
scientific instruments.
Operational
Readiness Review (ORR). The ORR at HFIR was the first to be conducted at any Category 1 DOE
facility since the current ORR guidance was issued. The ORR included a
comprehensive restart plan, independent-contractor and DOE reviews, and close
coordination with DOE headquarters and the site office.
Reactor operations were resumed on
December 18, 2001
Facility Improvements Support
Neutron Scattering Instrument Upgrades. New
monochromator drums were fabricated for the triple-axis spectrometers at HB-1,
2, and 3. A shielding tunnel and neutron guide were fabricated for HB-2, where a
20-cm-diameter beam tube was installed with beryllium inserts to support four
beam lines. The resulting beam intensity is expected to be three times that of
the original design for some of the instruments.
The Combustion Research Facility
Stagnation-flow
Reactor Designed to Probe High-temperature Chemistry.
Chemically
reacting flows at interfaces are an important class of processes occurring in
combustion, catalysis, thin film formation, and materials synthesis.
An innovative stagnation-flow reactor with access for optical diagnostics
and mass spectrometry is nearing completion and will provide a valuable tool for
probing high-temperature chemistry for a broad range of industrially relevant
processes.
Fiber-based Laser
Systems Developed. Fiber lasers and amplifiers are unique optical sources that provide many
advantages for detection of chemical and biological compounds.
The CRF has established the capability to fabricate them in-house.
The facility will allow the pursuit of new research in optical
diagnostics and will help DOE remain at the forefront of this field.
New Reactor
Allows Investigation of Gasification Processes.
The design and facility modifications have
been completed for a new reactor that will allow unprecedented optical access to
pressurized combustion and gasification processes.
This reactor will give the CRF the capability to investigate gas-phase
kinetics, materials behavior, advanced diagnostic development, and solid and
liquid fuel combustion chemistry and physics under pressurized conditions.
Selected FY 2001 Scientific
Highlights/Accomplishments
Materials
Sciences and Engineering Subprogram
Micro-size Light Emitters for Solid
State Lighting Applications. Energy
savings of tens of billions of dollars per year could be achieved by replacement
of household 100-watt light bulbs by white light emitting diodes (LED) made by
mixing LEDs emitting primary colors. However,
improved LED efficiency is necessary before such replacement becomes feasible.
New research has shown that interconnecting hundreds of micro-size LEDs
to replace larger conventional LEDs can boost the overall emission efficiency by
as much as 60 percent.
A New Method for Obtaining Crystal
Structures Without Large Crystals.
High-resolution x-ray diffraction using polycrystalline samples
(“powders”) rather than traditional single-crystal samples has advanced to
the point where the structures of complex materials including oxides, zeolites,
and small organic structures can be solved.
Advantages of powder diffraction are that it is not affected by crystal
fracture and polycrystalline samples can be formed over a much wider range of
conditions than large single crystals. Recently,
powder diffraction was demonstrated for large molecules, such as proteins, that
were considered far too complex for powder diffraction experiments.
In addition to the many important applications to materials sciences,
this technique will also be useful in chemistry and biosciences.
NMR
and MRI Outside the Magnet.
NMR (nuclear magnetic resonance) imaging and MRI (magnetic resonance
imaging) have required large high-field magnets that impose extremely uniform
magnetic fields upon the sample. In
many circumstances, however, it is impractical or undesirable to place or rotate
objects and subjects within the bore of such a large magnet.
A new approach for the recovery of highly resolved NMR spectra and MRI
images of samples in grossly non-uniform magnetic fields was recently
demonstrated. The approach will be
useful for the enhanced study of fluids contained in porous materials, such as
deep underground oil-well logging studies, and is expected to have dramatic
research applications in chemistry, materials sciences, and biomedicine.
Terabit
Arrays (One trillion bits per square inch). A 300-fold increase in
magnetic storage density has been achieved using a patented technique of
self-assembly of block copolymers under the influence of a small voltage.
The new technique is simple, robust, and extremely versatile.
The key to this discovery lay in directing the orientation of nanoscopic,
cylindrical domains in thin films of block copolymers.
By coupling this with routine lithographic processes, large area arrays
of nanopores can be easily produced. Electrochemical
deposition of metals, such as cobalt and iron, produces nanowires that exhibit
excellent magnetic properties, key to ultrahigh density magnetic storage.
The nanowires are also being used as field emission devices for displays.
Observations
of Atomic Imperfections.
A new electron beam technique has been developed that has measured atomic
displacements to a record accuracy of one-hundredth of the diameter of an atom.
Such small imperfections in atomic packing often determine the properties
and behavior of materials, particularly in nano-structured devices.
This capability has been made possible by a new technique that couples
electron diffraction with imaging technology.
The result is a greatly enhanced capability to map imperfections and
their resulting strain fields in materials ranging from superconductors to
multi-layer semiconductor devices.
Semiconductor
Nanocrystals as “Artificial Leaves.”
Recent experiments
demonstrated that carbon dioxide could be removed from the atmosphere with
semiconductor nanocrystals. These
“artificial leaves” could potentially convert carbon dioxide into useful
organic molecules with major environmental benefits. However, to be practical, the efficiency must be
substantially improved. New
theoretical studies have unraveled the detailed mechanisms involved and
identified the key factors limiting efficiency.
Based on this new understanding, alternative means for improving
efficiency were suggested that could lead to effective implementation of
artificial leaves to alleviate global warming and the depletion of fossil fuels.
"Magic"
Values for Nanofilm Thickness. A key issue for
nanotechnology is the structural stability of thin films and the devices made
from nanostructures. It was
recently demonstrated that nanofilms are significantly more stable at a few
specific values of film thickness. The
origin of this effect arises from the confinement of electrons within the film
leading to electronic states with discrete energy values, much as atomic
electrons are bound to the nucleus at discreet energy levels. Calculations demonstrated that increased stability occurred
when the number of electrons present in the film completely filled the set of
available states, just as filled electronic shells make the mobile gases very
stable.
Materials
Resistant to Damage from Nuclear Waste.
The ability to predict the composition and structure of materials that
are resistant to radiation damage, such as in nuclear waste storage, has been
formulated on a firm scientific basis. Current
nuclear storage materials cannot resist radiation damage for the required
thousands of years because radioactive emissions in a storage material jostle
atoms out of their carefully ordered arrangements.
These materials become unstable and eventually leach into the
environment. Computer simulations
and experiments revealed that a special class of complex ceramic oxides called
fluorites is able to resist this fate. The
fundamental principle is rather simple: the configurations of atomic
arrangements in these oxides are relatively disordered to begin with allowing
them to tolerate displaced atoms caused by radiation.
Brilliant
X-Rays Shine Light on Welds.
Using high-brightness synchrotron radiation, the details of
microstructural changes of welds were mapped and studied for the first time.
This advanced capability shows how the welding process alters the
structure and changes the properties of metals.
Its application is virtually unlimited, since it can investigate dynamic
changes in crystal structure near the melting point of any metal.
Knowledge gained from this award winning work on titanium and stainless
steels is being used to advance and refine theories and numerical models of
welding fundamentals. Dramatic
savings to the U.S. economy would result from better quality, more reliable
welds.
Micro
Lens for Nano Research.
A silicon lens that is 1/10 the diameter of a human hair has been
fabricated and used to image microscopic structures with an efficiency 1,000
times better than existing probes. The
combination of high optical efficiency and improved spatial resolution over a
broad range of wavelengths has enabled measurement of infrared light absorption
in single biological cells. This
spectroscopic technique can provide important information on cell chemical
composition, structure, and biological activity.
Nanofluids.
Nanofluids (tiny, solid nanoparticles suspended in fluid) have been
created that conduct heat ten times faster than thought possible, surpassing the
fundamental limits of current heat conduction models for solid/liquid
suspensions. These nanofluids are a
new, innovative class of heat transfer fluids and represent a rapidly emerging
field where nanoscale science and thermal engineering meet.
This research could lead to a major breakthrough in making new composite
(solid and liquid) materials with improved thermal properties for numerous
engineering and medical applications to achieve greater energy efficiency,
smaller size and lighter weight, lower operating costs, and a cleaner
environment.
Chemical Sciences, Geosciences,
and Energy Biosciences Subprogram
Capturing
Molecules in Motion with Synchrotron X-Ray Pulses.
Photochemical conversion of solar energy depends on light-driven chemical
reactions. Absorption of light
ultimately leads to atomic rearrangements necessary to produce photochemical
products. The intermediate
molecular configurations created by absorption of light are short-lived and
their structures are largely unknown. In
novel experiments at the Advanced Photon Source, molecular structures of
laser-generated reaction intermediates in solutions, having lifetimes as short
as 28 billionth of a second, have been obtained. Future experiments are planned that will allow for capture of
intermediate structures on even shorter time scales. These studies are providing the fundamental knowledge needed
to develop artificial photoconversion devices.
Early Precursor Identified in Water
Radiolysis. Radiolytic
decomposition of water produces hydrogen gas, which is flammable and potentially
explosive. This is of concern in
maintenance of water-moderated nuclear reactors, long-term storage of
transuranic fissile materials containing adsorbed water, and management of
high-level mixed-waste storage tanks. In
recent studies on the effects of ionizing radiation on condensed media, a common
precursor to essentially all hydrogen from irradiated water has been discovered.
This precursor is a solvated electron.
External intervention and capture of this precursor can prevent the
generation of hydrogen gas from water. The
reactivity of the precursor with a large number of scavengers has previously
been determined in pulse radiolysis experiments, thus a priori predictions can
be made on the efficiency of the intervention and prevention of gas generation.
The
World's Smallest Laser.
A team of materials scientists and chemists has built the world's
smallest laser - a nanowire nanolaser 1,000 times thinner than a human hair.
The device, one of the first to arise from the field of nanotechnology,
can be tuned from blue to deep ultraviolet wavelengths.
Zinc oxide wires only 20 to 150 nanometers in diameter and 10,000
nanometers long were grown, each wire a single nanolaser.
Discovering how to excite the nanowires with an external energy source
was critical to the success of the project.
Ultimately, the goal is to integrate these nanolasers into electronic
circuits for use in "lab-on-a-chip" devices that could contain small
laser-analysis kits or as a solid-state, ultraviolet laser to allow an increase
in the amount of data that can be stored on high-density optical disks.
Polymerization
to Make Plastics.
The discovery of metallocene catalysts caused major advances in
polymer production (e.g., polyethylene, polypropylene), the most widespread of
synthetic materials. The ability to
control the orientation of each link of a polymer chain allows control of
crystallinity, density, softening point, and other important properties.
A recent improvement in these catalysts is the synthesis of bimetallic
complexes in which two catalytic centers and two cocatalytic centers are held in
close proximity in solution or adsorbed on surfaces.
By altering the nature of the centers, it is possible to control rate of
reactivity, the degree of chain branching, and plastic rigidity.
First
Ever Chemistry with Hassium, Element 108.
Element 108 - hassium - was discovered in 1984.
It does not exist in nature but must be created one atom at a time by
fusing lighter nuclei. Recently,
the first experiments to examine its chemical properties were performed by an
international team (German, Swiss, Russian, Chinese and American scientists) at
the Gesellschaft für Schwerionenforschung (GSI) in Darmstadt, Germany using
novel techniques developed at the Lawrence Berkeley National Laboratory.
Energetic magnesium projectiles bombarded targets of curium, a rare
artificial isotope produced and processed at Oak Ridge National Laboratory.
The hassium atoms formed by impacts between beam and target reacted with
oxygen to form hassium oxide molecules enabling the study of the properties of
this new chemical compound. The
chemistry of man-made and heavy elements, particularly chemistry impacting
environmental insults, is of major interest, and these experiments are a first
step for this element.
Improved
Materials for Fuel Cells.
Major impediments for the commercialization of fuel cells include the
inability to use hydrogen fuel containing traces of carbon monoxide and the
necessity of using large amounts of expensive platinum catalysts.
A novel ruthenium/platinum catalyst has been produced through a new
preparation method involving spontaneous deposition of platinum on metallic
ruthenium nanoparticles. The
resulting catalyst has a higher carbon monoxide tolerance than commercial
catalysts and uses smaller amounts of platinum.
Platinum
Encrusted Diamond Films.
Research on new catalytic electrodes, e.g., for fuel cells, has shown
that synthetic diamond thin films are excellent supports for catalysts because
of their corrosion resistance. The challenge to produce an electrode is to
incorporate nanometer sized platinum and platinum/ruthenium catalyst particles
into the surface structure of the diamond film. Recently, the ability to incorporate 10 to 500 nanometer
diameter particles into the bulk structure of the films has been demonstrated.
These new surface modified systems may result in significantly improved
catalytic activity and stability, and could have even broader applications in
chemical synthesis, toxic waste remediation, and chemical and biomedical
sensors.
Complex
Flow in the Subsurface.
Recovery of subsurface fluids, whether oil and gas or contaminants,
requires understanding the way fluids flow within porous and fractured rocks and
soil. This is particularly
complicated when there are multiple fluids (oil-methane-water; water-carbon
dioxide). New experiments combined
with theory and computational modeling have tracked the simultaneous flow of two
fluids in fractured and porous media. Flow
paths of both fluids are significantly longer than under single fluid conditions
and transport is very sensitive to differences in fluid structure.
Complete
Plant Genome of the First Model Plant. The first complete
sequencing of a plant genome was completed by an international consortium of
researchers from Europe, Japan and the U.S.
The DOE was one of the supporters of the U.S. effort.
The sequencing of the genome of Arabidopsis will provide the information
needed to increase food production in an energy-efficient and environmentally
friendly manner, provide increased wood and fiber production, and increase the
use of plant materials for energy and the production of petroleum-replacing
chemicals.
Selected
FY 2001 Facility Accomplishments
The four synchrotron radiation light sources
and three BES neutron scattering facilities served 6,982 users in FY 2001 by
delivering a total of 26,476 operating hours to 204 beam lines at an average of
96.1% reliability (delivered hours/scheduled hours).
The High Flux Isotope Reactor at Oak Ridge National Laboratory did not
operate in FY 2001 due to the installation of upgrades.
Statistics for individual facilities are provided below.
In one instance, less time was needed for maintenance activities than was
scheduled, so more time was delivered to users than planned.
The maximum number
of total operating hours for these 7 facilities is estimated to be about 37,100
hours. Most of the BES facilities
already operate close to the maximum number of hours possible for their
facility. The next priority is to
support and maintain beamlines and instruments at the state-of-the art.
For the synchrotron radiation light sources and the neutron scattering
facilities, the number of beamlines and instruments would need to be increased
in order to achieve the full capacity of each of the facilities.
Capacity at the light sources could increase by nearly a factor of two if
all beamlines were fully instrumented. Capacity
at the neutron sources could also increase substantially by upgrading existing
instruments and fabricating new ones.
BES defines "users" as researchers who conduct
experiments at a facility (e.g., received a badge) or receive primary services
from a facility. An individual is
counted as one user per year regardless of how often he or she uses a given
facility in a year. “Operating
hours” are the total number of hours the facility delivers beam time to its
users during the Fiscal Year. Facility
operating hours are the total number of hours in the year (e.g., 365 days
times 24 hour/day = 8,760 hours) minus time for machine research, operator
training, accelerator physics, and shutdowns (due to maintenance, lack of
budget, faults, safety issues, holidays, etc.).
The
Advanced Light Source (ALS)
served 1,163 users in FY 2001 by delivering 5,261 operating
hours to 37 beam lines at 96.2% reliability (delivered hours/scheduled hours).
The ALS is supported by the Materials Sciences and Engineering
subprogram.
A new beamline for x-ray microscopy of polymers.
Owing to its elemental and chemical
specificity, x-ray microscopy is a superior tool for the study of multicomponent
polymers. A scanning x-ray
microscope that is specifically optimized to the demands of polymer research is
being commissioned.
Ambient-pressure
photoemission spectroscopy. The
real world of chemistry, biology, and environmental science is a world that is
frequently wet, hot, and under atmospheric or higher pressures, whereas
experimental measurements are often best done under vacuum with cold samples.
One step toward bridging the gap is the development of a new experimental
chamber for in-situ investigation of samples under ambient conditions.
Interferometer controls scanning x-ray microscope.
In scanning microscopy, it is essential to
locate and control the position of the probe over the sample.
A control system developed for a scanning x-ray microscope is able to
position the x-ray beam with nanometer accuracy, so that features in the sample
can be studied at the finest spatial resolution of the instrument.
Superbend beamlines developed. To broaden the spectral range of the Advanced Light Source
to cover shorter wavelengths, superconducting bend magnets were designed.
The first two beamlines will be implemented sequentially over the next
year to serve protein crystallographers and to provide much needed harder x-ray
sources for ALS diffraction studies.
The
Advanced Photon Source (APS)
served 1,989 users in FY 2001 by delivering 4,788 operating
hours to 37 beam lines at 95.8% reliability (delivered hours/scheduled hours).
The APS is supported by the Materials Sciences and Engineering
subprogram.
Storage ring “top-up operation” becomes routine.
After successful tests with 25% of the scheduled user-beam time dedicated
to top-up operation, the APS is scheduling the majority of future operations for
top-up mode. During top-up operation, injecting a pulse of electrons once
every two minutes holds the stored current constant to 0.2 percent.
This operating mode delivers a constant heat load on x-ray optics and
various accelerator components, thus improving the x-ray beam stability.
It also allows flexibility in operating modes, which are traditionally
limited by the short lifetime of the stored beam.
Top-up operation has significantly enhanced the research capabilities of
the APS.
Two undulators on a single straight section deliver two
independent x-ray beams to users. For
the first time, a novel concept of spatially separating the beams from two
insertion devices placed on single straight section was realized.
This was accomplished by placing the undulator axes at a small angle with
respect to each other. Successful
implementation of this concept enabled 100% efficient utilization of the
delivered beam.
Low-emittance lattice developed. Machine studies have successfully established operating
conditions for the APS storage ring with the horizontal emittance reduced by
approximately a factor of two. This
reduces the horizontal source size and divergence of the x-ray beam and results
in at least a factor of two improvement in the overall brilliance.
Initial user results are encouraging and routine operation with this mode
is scheduled for the near future.
The
National Synchrotron Light Source (NSLS)
served 2,523 users in FY 2001 by delivering 5,556
operating hours to 86 beam lines at 100.0% reliability (delivered
hours/scheduled hours). The NSLS is
supported by the Materials Sciences and Engineering subprogram.
Polarization modulation spectroscopy for magnetism research.
A
new high-resolution soft x-ray beamline and a phase sensitive detection system
were completed to take advantage of the fast switching capability of the
Elliptically Polarized Wiggler. The
new system provides high sensitivity and enables magnetic field dependent
studies.
Focusing of high energy x-rays with asymmetric Laue crystals. Theoretical prediction
and experimental verification of a new concept for focusing of high energy
x-rays was demonstrated. This new
design results in a more than 100 fold increase in the photon flux delivered to
the sample. A new monochromator
based on this design was constructed and implemented at the superconducting
wiggler beamline for high pressure and materials research.
High magnetic field, far-infrared spectroscopy beamline
commissioned. A
new high magnetic field, far-infrared beamline was commissioned with a
far-infrared spectrometer and 16 Tesla superconducting magnet. Combining this with a high-field magnet system opens up new
opportunities for measuring electron spin resonance (ESR), cyclotron resonance,
and other magneto-optic effects in solids.
X-ray optics for microbeam diffraction, elemental mapping,
and high pressure research developed. A
new system for micro-focusing of x-rays was implemented, achieving a focus of 3
microns (vertical) by 9 microns (horizontal).
The system has been used in the study of bone diseases, materials under
high pressure, and semiconductors.
High gain harmonic generation (HGHG) free electron laser
(FEL) achieves saturation. By
frequency multiplying and amplifying a seed laser signal, an HGHG FEL imposes
the properties of the laser onto the FEL output beam. In a demonstration, light at long wavelength was frequently
doubled. Full characterization of
the FEL light and its harmonics agreed with theory and demonstrated the utility
of an HGHG FEL for producing intense coherent light pulses.
The
Stanford Synchrotron Radiation Laboratory (SSRL)
served 907 users in FY 2001 by
delivering 4,539 operating hours to 25 beam lines at 94.9% reliability
(delivered hours/scheduled hours). The
SSRL is supported by Materials Sciences and Engineering subprogram.
Stanford-Berkeley synchrotron radiation summer school.
The first Stanford-Berkeley summer school
on synchrotron radiation and its applications was held with 36 students from a
diverse range of scientific fields. The
goal was to introduce young scientists to the fundamental properties of
synchrotron radiation and the understanding and use of several techniques,
including spectroscopy, scattering, and microscopy.
New actinide facility commissioned.
Synchrotron-based measurements are a
crucial part of chemical and materials research programs involving radionuclides
and radiologic materials. In order
not to limit the scope of experiments that can be performed, a radiologic sample
analysis facility has been integrated into a modern synchrotron beamline.
This combination insures safe handling of actinide and other radiology
materials and also provides state-of-the-art measurement capabilities that have
proven extremely useful in remediation efforts.
Materials science small angle x-ray scattering beamline
facility completed. The
materials science small and wide-angle x-ray scattering station is now in full
user operation. The integrated
beamline and experimental equipment facility allows for studies of weakly
scattering systems, such as dilute polymer solutions.
Microfocus optics system for X-ray micro-spectroscopy.
An experimental apparatus employing tapered
metal capillary optics for conducting X-ray micro-spectroscopy is now in
operation. This capability allows
X-ray micro-spectroscopy experiments in the materials, biological, and
environmental sciences.
Successful 3 GeV injector test. The SPEAR injector was successfully run at 3 GeV, proving
that it is ready to provide at-energy injection for SPEAR3.
The 3 GeV test came toward the end of the two-year Injector Upgrade
Accelerator Improvement Project, in which power supplies, magnets, and
diagnostics were upgraded to insure reliable 3 GeV operation.
At-energy injection will improve SPEAR3 performance by providing better
fill-to-fill orbit reproducibility and thermal stability.
RF waveguide dampers improve beam stability and lifetime.
RF
waveguide dampers were installed in the two radio frequency (RF) waveguides in
the SPEAR storage ring to eliminate high frequency oscillations excited by the
electron beam in the RF cavity/waveguide system.
The dampers not only eliminated the instabilities but they allowed the
use of operations parameters that gave a 20% improvement in the electron beam
lifetime.
The
Intense Pulsed Neutron Source (IPNS)
served 240 users in FY 2001 by delivering 3,968 operating hours to 13 beam lines
at 102.6% reliability (delivered hours/scheduled hours).
The IPNS is supported by the Materials Sciences and Engineering
subprogram.
IPNS hosts the national neutron and x-ray scattering school.
In
August 2001, Argonne National Laboratory again hosted the two-week National
School on Neutron and X-Ray Scattering. The
school continues to attract outstanding graduate students and post-doctoral
appointees with 179 applications for the 60 available positions.
Upgrade of IPNS instruments. The High Resolution Medium Energy Chopper Spectrometer
(HRMECS) instrument was completely upgraded and a chopper was added to the
General Purpose Powder Diffractometer (GPPD).
The HRMECS upgrade included the complete overhaul of data
collection/control software and hardware, addition of position-sensitive
detectors at low scattering angles and improved neutron choppers.
The T0 chopper on GPPD blocks high energy neutron from entering the
diffractometer.
Auto-anneal capabilities added to moderator system.
Regular annealing required for IPNS’s
unique ultra-cold moderator has been accomplished by installing a system that
automatically anneals the solid methane moderator every three days.
This automation allows for reduced manpower and improved operation of the
IPNS target moderator assembly.
The
Manuel Lujan Jr. Neutron Scattering
Center at the Los Alamos Neutron Science Center (LANSCE)
served 122 users in FY 2001 by delivering 2,364 operating hours to 6 beam lines
at 82.0% reliability (delivered hours/scheduled hours).
The Lujan Center is supported by the Materials Sciences and Engineering
subprogram.
served 122 users in FY 2001 by delivering 2,364 operating hours to 6 beam lines
at 82.0% reliability (delivered hours/scheduled hours).
The Lujan Center is supported by the Materials Sciences and Engineering
subprogram.
HIPPO diffractometer commissioned.
Following three years of design and
construction, the recently completed HIPPO (High Pressure, Preferred
Orientation) diffractometer took its first neutron-beam-related diffraction
pattern on a sample of nickel on July 7, 2001.
The scientific thrust of this new state-of-the-art spectrometer is the
investigation of dynamic processes in heterogeneous bulk materials in a variety
of environments.
SMARTS will provide new capabilities in materials research.
SMARTS,
a third generation neutron diffractometer for the study of polycrystalline
materials, received its load frame and furnace, which were successfully tested
onsite during 2001. SMARTS is
scheduled to receive first beam in August 2001, followed by commissioning
through the remainder of the year.
BES partners on new institutional instruments.
Three institutionally funded instruments,
ASTERIX, PHAROS, and IN500 were supported in part under the auspices of BES.
ASTERIX produces a highly polarized intense beam of cold neutrons that
has a very large cross section and covers a wide wavelength range while
minimizing the fraction of the neutron beam that is not used.
PHAROS, a high-resolution chopper spectrometer, is designed for low-angle
studies. IN500 is a cold neutron
time-of-flight spectrometer, which will offer all the advantageous capabilities
of reactor-based instruments.
Instrument performance improves with use of new chopper
technology. All
of the Lujan Center's new instruments and some of the existing instruments have
enjoyed dramatic improvements in chopper technology in FY 2001.
These performance improvements in two technical areas, timing reference
generators and chopper controls, now enable the accelerator and all neutron
choppers to run as slaves of the master timing generator.
This success in chopper technology has drawn the attention of several
other spallation neutron facilities and has redefined the timing specifications
for the Spallation Neutron Source.
Upgrades to small-angle scattering instrument.
A new frame-overlap chopper was procured
and installed, which enables the small-angle scattering instrument, LQD, to make
full use of the higher flux it enjoys from the hydrogen moderator installed over
the last two years. Recent
additions to LQD also include a gravity-focusing device, which compensates for
gravitational drop, especially for slow neutrons.
Upgrades to SPEAR improve instrument performance.
SPEAR (Surface Profile Analysis
Reflectometer) is used for determining chemical density profiles at solid/solid,
solid/liquid, solid/gas, and liquid/gas interfaces.
Upgrades to SPEAR during 2001 included the installation of shutter
hardware to reduce closure time, and additional automation of flight-path
components. For better performance,
an evacuated flight path, and two digital chopper controllers were added.
In addition, a new collimation system, together with improved software,
allowed for the first real-time reflectivity measurements. These upgrades were made to make the instrument
user-friendlier.
The
High Flux Isotope Reactor (HFIR)
served 38 users in FY 2001 by delivering 8 operating hours for materials
irradiation and institutes that utilize the transplutonium program and medical
isotopes. The reactor was shut down
at 8:00 a.m. on October 1, 2000, for the scheduled replacement of the beryllium
reflector and installation of upgrades and remained shutdown for the remainder
of the year. The HFIR is supported by the Materials Sciences and
Engineering subprogram.
Installation of new components enhances scientific
capabilities at HFIR. Many
of HFIR’s internal components have been replaced with new, upgraded components
that will significantly enhance its neutron scattering research capabilities
without diminishing its isotope-production or material-testing capabilities.
Replaced components include the beryllium reflector, its support
structure, and three of the four neutron beam tubes.
Beam intensity for some instruments is expected to be three times that of
the original design.
Cold Source Project progress. The moderator vessel has been fabricated and has passed
acceptance pressure tests at room and liquid-nitrogen temperatures.
Spectrometers for cold neutron research.
The cold source to be installed at HFIR
will provide long wavelength neutron beams that are unsurpassed worldwide.
Instrumentation has been designed to make optimum use of the cold neutron
beams. Instruments include small
angle spectrometers for measurements on large-scale structures, reflectometers
for the study of surface phenomena, and triple-axis spectrometers for the
determination of low-energy excitations.
Spectrometers for thermal neutron research.
The larger beam tubes and new mochromator
drums installed at HFIR will permit considerable gains in intensity for the
thermal neutron spectrometers, by as much as a factor of five.
The
Combustion Research Facility (CRF)
is supported by the Chemical Sciences, Geosciences, and Energy
Biosciences subprogram.
New capabilities. The
CRF provides a primary interface for the integration of BES programs with those
of DOE's Offices of Energy Efficiency and Renewable Energy and Fossil Energy
related to combustion by collocating basic and applied research at one facility.
Three laboratories were completed. The
particle diagnostic laboratory can now generate flames with controllable fuel
and oxidizer feeds to develop a fundamental understanding of small particle
formation from combustion sources. A
time-resolved fourier transform spectrometer for chemical kinetics and dynamics
studies is now available in the kinetics and mechanisms laboratory.
Related to applied research, the investigation of a novel engine
combustion concept is being conducted in the new homogeneous-charge,
compression-ignition engine laboratory.
New capabilities. The
CRF provides a primary interface for the integration of BES programs with those
of DOE's Offices of Energy Efficiency and Renewable Energy and Fossil Energy
related to combustion by collocating basic and applied research at one facility.
Three laboratories were completed. The
particle diagnostic laboratory can now generate flames with controllable fuel
and oxidizer feeds to develop a fundamental understanding of small particle
formation from combustion sources. A
time-resolved fourier transform spectrometer for chemical kinetics and dynamics
studies is now available in the kinetics and mechanisms laboratory.
Related to applied research, the investigation of a novel engine
combustion concept is being conducted in the new homogeneous-charge,
compression-ignition engine laboratory.
New capabilities. The
CRF provides a primary interface for the integration of BES programs with those
of DOE's Offices of Energy Efficiency and Renewable Energy and Fossil Energy
related to combustion by collocating basic and applied research at one facility.
Three laboratories were completed. The
particle diagnostic laboratory can now generate flames with controllable fuel
and oxidizer feeds to develop a fundamental understanding of small particle
formation from combustion sources. A
time-resolved fourier transform spectrometer for chemical kinetics and dynamics
studies is now available in the kinetics and mechanisms laboratory.
Related to applied research, the investigation of a novel engine
combustion concept is being conducted in the new homogeneous-charge,
compression-ignition engine laboratory.
New capabilities. The
CRF provides a primary interface for the integration of BES programs with those
of DOE's Offices of Energy Efficiency and Renewable Energy and Fossil Energy
related to combustion by collocating basic and applied research at one facility.
Three laboratories were completed. The
particle diagnostic laboratory can now generate flames with controllable fuel
and oxidizer feeds to develop a fundamental understanding of small particle
formation from combustion sources. A
time-resolved fourier transform spectrometer for chemical kinetics and dynamics
studies is now available in the kinetics and mechanisms laboratory.
Related to applied research, the investigation of a novel engine
combustion concept is being conducted in the new homogeneous-charge,
compression-ignition engine laboratory.
Selected FY 2000 Scientific
Highlights/Accomplishments
Materials
Sciences
Subprogram
Magnetism
at the atomic scale. When information is written to a computer hard drive, local magnetic
moments associated with atoms in a small region of the surface reverse direction
like sub-microscopic compass needles. A
new theory has helped explain these dynamical processes. This work recently
received the Gordon Bell Award for the fastest real supercomputing application
and was named to the Computerworld Smithsonian 2000 collection for being the
first supercomputing application to surpass one teraflop.
Functional
nanostructured materials that replicate natural processes.
A newly developed class of nanostructured materials can selectively
filter molecules by their size and chemical identity.
These remarkable materials are made from a solution of molecular building
blocks that spontaneously arrange themselves into a porous solid as the solvent
evaporates. This achievement
involved creating the self-organizing precursors, controlling the pore size, and
employing a novel evaporation process that promotes self-assembly. These materials hold the promise for significant applications.
For example, in the future we may wear “breathing” fabrics that block
hazardous chemicals while admitting benign species like oxygen.
The
Library of Congress on a single disk?
The vision that information can be written and erased near the single
molecule limit has been realized for the first time.
Disordering and re-ordering tiny regions of a thin film show promise for
storing a million times more information than with today's computer disks with
no increase in space. The film is
made of organic material and supported by graphite.
It is so thin that 40,000 layers would be only as thick as a sheet of
paper. By exposing the film to
voltage pulses with a scanning tunneling microscope, nanometer-sized regions can
be switched from crystalline to disordered, increasing their ability to conduct
electricity by 10,000 times. Each
tiny region is one bit of information, not much bigger than a single molecule of
the film.
Analyses
of nanocrystals using coherent (laser-like) synchrotron radiation.
A
powerful new x-ray diffraction method for characterizing the structure of
nanocrystalline solids has been developed.
Tailoring nanocrystalline properties for specific applications depends
critically on detailed knowledge of three-dimensional structure.
Traditional x-ray diffraction methods are inadequate; however, coherent
x-ray diffraction patterns of gold nanocrystals show surface facets, fringes due
to interference among facets, nanocrystal lattice distortion, and, ultimately,
equilibrium nanocrystal shape.
Ion-implantation
for strong metal-ceramic bonds.
Ceramics are hard and corrosion
resistant but fracture easily. Metals
resist fracture but are not as wear or corrosion resistant as ceramics. Coating a metal with a ceramic is a way to improve both.
However, current coating technologies can degrade the performance of
metals. A new approach has been
successfully developed that employs ion-beam intermixing of the coating with the
metal from collision cascades, which are microscopic (nanometer-sized)
“hot-zones” formed along the ion track.
Since the heating in collision cascades is very short and localized,
macroscopic heating of the metal does not occur.
A patent has been filed using this new approach to improve hip, knee, and
dental prosthetic devices. Ion
implantation is used to coat the bone mineral (hydroxyapatite) on titanium
starting with a high density layer bonded well to the titanium and changing
progressively toward a porous bone mineral outer surface that promotes bone
growth and bonding to bone.
Long-term
storage of plutonium. Worldwide,
nuclear energy production and defense programs have created 1,350 metric tons of
plutonium. Because plutonium is
radiotoxic and has a long half-life (24,500 years), a long-term storage solution
must immobilize plutonium in materials that are resistant to radiation damage
for millennia. Using heavy-ion
irradiation, advanced characterization techniques, and computer simulation
methods, researchers have discovered that highly durable gadolinium zirconate
can lock plutonium into its structure while remaining resistant to radiation
damage for millions of years.
Boron
doping of silicon semiconductor devices -- faster, lower-power computing.
Boron doping of silicon improves electrical conductivity and other
important aspects of silicon device performance.
A fifty-fold increase in active boron doping -- far above nature’s
maximum of 0.01 percent -- has been achieved using a new process involving
atomic hydrogen. Resulting
ultra-highly doped silicon layers provide self-aligned "metallic"
contacts, improve semiconductor devices, eliminate etching steps in device
fabrication, reduce manufacturing costs, and minimize the use of toxic etching
gases and chemicals.
Seeing
electrons.
A novel, quantitative, and highly sensitive method has been developed to
image and measure the distribution of valence electrons, which are responsible
for chemical bonding and the transport of electrical charge in solids.
This new technique, combining imaging and diffraction in the electron
microscope, was used to reveal the spatial distribution of valence electrons in
complex structures of high-temperature superconductors. The ability to directly
observe and measure valence electron distributions with atomic scale resolution
will greatly help in the search for better superconductors, ferroelectrics, and
semiconductors.
Fluctuation
microscopy.
Fluctuation microscopy, a new discovery, challenges the common perception
that glassy materials have no organization.
Fluctuation microscopy relies on the ability of the electron microscope
to measure diffraction from tiny volumes (~1000 atoms).
It is based on detailed computational simulations coupled with
computer-assisted statistical analysis of multiple electron images.
It has required development of advanced image-detection methods. In one of the first
applications of this method, studies of amorphous silicon and germanium show
that both are highly organized over distances of tens of atoms, even though
other measurement techniques see these atoms as completely random.
This finding is critical to improving the ability of amorphous solar
cells.
A
smart transistor. A
breakthrough in developing the world's smartest transistor has been
accomplished. Germanium-based
transistors using a new ferroelectric dielectric would be “smart” devices
capable of remembering their state. The
heart of this new scientific advance is the understanding of the relationship
between polarization and microstructure and how to control it. This
breakthrough offers enormous potential for energy savings in a myriad of
electronic sensors and devices as no power is necessary to maintain a given
on/off state. A low-power, gigabyte
chip could thus serve as a computer hard drive.
Design
of semiconductors with prescribed properties.
A theoretical method has been invented by which one can first specify the
properties desired in a semiconductor and then work backward to predict the
structure of the material that will show those properties.
This work was featured in Fortune
Magazine.
Chemical Sciences
Subprogram
Direct
measurement of chemical reactions in turbulent flows. Long known for their dramatic advancements in laser
instrumentation for monitoring gas-phase reactions and chemically reacting
flows, scientists at the Combustion Research Facility have for the first time
monitored multiple flame species directly and simultaneously.
These measurements provide a powerful test of combustion models that
could lead to improved combustion efficiency.
Dynamics
of a single molecules. Reactions of single molecules have been observed by
monitoring molecular fluorescence using newly developed experimental methods,
thus separating the effects of the motion of one molecule from the ensemble
motion of the molecule in its environment.
The dynamics of a single molecule have been shown to be significantly
different from motion in an ensemble, and should lead to the development of new
theories for predicting chemical reactivity.
Blinking
quantum dots. Quantum dots -- nanometer-size particles in which electrons
are confined in a relatively small volume -- have recently been shown to emit
light at multiple wavelengths, blinking on and off on a time-scale of seconds.
This remarkable behavior, attributed to luminescence from different
electronic states, has potential applications for optical logic and photonics
and may one day lead to nano-scale computers and/or portable analytical
instrumentation.
Generation
of laser-like x-ray beams.
Combining
state-of-the-art ultrafast laser systems with evolutionary computer algorithms
has led to a dramatic new demonstration of the controlled generation of coherent
x-rays. This represents an
important new source of ultrafast, coherent soft x-rays for studies of materials
properties and chemical physics.
Biomolecular
photobatteries. Voltages have been measured from a single photosynthetic
reaction center -- the five nanometer wide molecular structure in green plants
that captures solar energy and converts it into electrical energy.
The reaction center may be thought of as a tiny photobattery.
The reaction center functions as nanometer-sized diodes with possible
applications to molecular scale logic devices and computers.
Radiation
induced chemistry. Solid particles have been found to enhance the effects of
water radiolysis and the resulting production of hydrogen. Furthermore, gas bubbles form on the particles and that
impedes the continuous, safe release of hydrogen from the suspension. These
results may provide an explanation for the “burps” in storage tanks
containing aqueous suspensions and radioactive material.
Plutonium
chemistry in the environment. Using
newly constructed beamlines at the BES synchrotron radiation light sources,
scientists are now able to study small quantities of radioactive materials.
X-ray absorption studies on plutonium-containing soils from Rocky Flats
revealed that the plutonium is predominantly present as the solid oxide, PuO2,
a form substantially less mobile in soil and ground water than other possible
forms. This result demonstrates that the plutonium will remain stable and has
led to substantial cleanup cost savings.
Actinide
supramolecular complexes.
Researchers have for the first time built a
supramolecular actinide complex. Supramolecular
complexes are molecules that are built from smaller subunits, yet retain their
own distinct molecular properties. While
there may be future applications in separation science and catalysis, the
current worldwide effort in supramolecular chemistry is to understand the
principles that govern assembly of such molecules.
Molecular
theory of liquids. A molecular theory for the liquid state, which has eluded
scientists for years, has now been developed. This provides new opportunities in
one of the most important areas for process engineering and one of its most
perplexing problems - the prediction of liquid-gas equilibria based on the
well-known properties of molecules.
Engineering and
Geosciences Subprogram
Engineering at the nanoscale.
Using nanoscale devices in real-world engineered systems is one of the
greatest challenges facing nanoscale research.
A portfolio of research activities explores how to engineer at the
nanoscale. Recent activities
include the development of physics-based models to represent crack initiation as
a nanoscale phenomenon; studies of the frictional response of nanochains;
electric charge transfer in semiconductor nanostructures; nanoscale quantum-dot
self assembly using DNA templates; and the integration of nanoscale biomotors
with mechanical devices. In this
last activity, researchers constructed integrated nanoscale devices that are
powered by biomolecular motors and fueled by light.
In one such system, a protein from a photosynthetic bacterium generates
an electrochemical gradient across an artificial membrane system.
This system is chemically closed, enabling the motors to be continuously
supplied with fuel using a total light collection area less than 400 square
nanometers.
Geosciences imaging from the atomic
scale to the kilometer scale.
Advances in geosciences imaging were demonstrated this year at a variety
of disparate length scales. At the
smallest length scale, the GeoCARS beamline at the Advanced Photon Source was
used to examine the interaction of liquid water with alumina as a model for
understanding aluminum containing minerals such as clays.
Unlike other techniques used to characterize surfaces, the new beamline
can study wet crystal surfaces. The
result showed a significant change from the experiments using dry surfaces and
will help researchers understand water-solid interactions in nature at the
atomic level. At an intermediate
length scale, researchers are using advanced laser scanning confocal microscopy
to image, reconstruct, and characterize fluid flow through pores and cracks. Predicting the magnitudes and directions of flow in earth
material is critical in performance assessment of oil and gas reservoirs.
Finally, at the largest length scales, researchers are using specially
instrumented regions in an earthquake zone to help model and improve geophysical
imaging on the kilometer scale.
Biogeochemistry.
It is increasingly evident that living processes play a fundamental role
in determining the geochemistry of groundwater, near-surface sediments, and
deeper rocks. Microbes affect the
weathering of rocks and minerals, and microbial metabolism affects the
accumulation of heavy metals in soils or their release to groundwater.
These and other processes determine how soils, sediments, and ore bodies
form and how water quality is affected. Work
identifying how microbes affect the fate of zinc released to groundwater
percolating through lead-zinc mines and other biogeochemistry work recently led
to the award of MacArthur Foundation Fellowship to a BES supported researcher.
Biogeochemistry, which links three BES subprograms, is expected to play
an increasingly important role in addressing DOE missions.
Energy
Biosciences Subprogram
Completion
of the gene sequence of Arabidopsis
thaliana, the first plant genome.
Arabidopsis thaliana, a small
weed belonging the mustard family, became the world’s “model” plant owing
to its small physical size, small genome size, low level of junk and repetitive
DNA, short life cycle, large number of mutations, and ease in genetic analysis.
An international collaboration involving scientists from the U.S.,
Europe, and Japan announced the completion of the complete sequence of this
plant genome in December 2000. The Arabidopsis genome is entirely in the public domain, making the
results available to scientists worldwide.
The Energy Biosciences subprogram has been a partner in this project
since its inception; support for research on Arabidopsis dates to the early 1980s.
Snapshot
of a light-driven pump.
Sunlight causes the bacteriorhodopsin protein to change shape, and in the
process transport protons across a membrane to provide chemical energy.
X-ray crystallographic structure determinations of this light-driven
proton pump captured for the first time the molecule frozen mid-stroke of this
shape modification. This novel view
of the intermediate conformation enables us to see how biological nanostructures
capture and transform energy.
Selected
FY 2000 Facility Accomplishments
The four BES synchrotron
radiation light sources served 6,009 users in FY 2000 by delivering a total of
19,854 operating hours to 184 beam lines at an average of 99.5% reliability
(delivered hours/scheduled hours). The
three BES neutron scattering facilities served 524 users in FY 2000 by
delivering a total of10,395 operating hours to 34 beam lines at an average of
94.7% reliability (delivered hours/scheduled hours).
Statistics for individual facilities are given below.
“Users” are defined by BES as
researchers who conduct experiments at a facility (e.g., received a badge) or
receive primary services from a facility. An
individual is counted as one user per year regardless of how often he or she
uses a given facility in a year. “Operating
hours” are the total number of hours the facility delivers beam time to its
users during the Fiscal Year. Facility
operating hours are the total number of hours in the year (e.g., 365 days times
24 hour/day = 8,760 hours) minus time for machine research, operator training,
accelerator physics, and shutdowns (due to maintenance, lack of budget, faults,
safety issues, holidays, etc.).
The
Advanced Light Source (ALS) served
1,036 users in FY 2000 by delivering 5,367 operating hours to 34 beam lines at
95.0% reliability (delivered hours/scheduled hours).
The ALS is supported by the Materials Sciences subprogram.
New
technique for improved storage-ring stability. The electron beam parameters in the storage ring determine x-ray beam
lifetime and stability. Using a
mathematical technique, accelerator physicists have understood the strength and
location of harmful resonances that cause irregular, chaotic electron behavior
leading to loss of electrons from the beam.
Third-harmonic
cavities enhance beam lifetime.
The electron beam lifetime in a synchrotron-radiation source determines
how long users can record data before being interrupted when accelerator
operators replenish the train of short bunches that make up the beam. A
desirable way to increase the lifetime is to lengthen the bunches.
Five new third-harmonic cavities accomplish the bunch lengthening and
have increased electron beam lifetime increased by about 50%.
X-ray
science possible at femtosecond speeds. X-ray
experiments to study physical, chemical, and biological processes that occur on
a time scale of one molecular vibration (typically 100 femtoseconds) are an
emerging area of research. Three
developments at the ALS brought x-ray science into the femtosecond realm.
First, researchers developed a high-speed x-ray detector (a streak
camera) with a picosecond time resolution.
Second, researchers showed how to use a femtosecond laser to
"slice" tiny slivers from the circulating electron bunches in the
storage ring and use them to produce pulses of synchrotron radiation lasting
just 300 femtoseconds. Finally,
accelerator physicists devised an arrangement of magnets that allow a narrow-gap
undulator optimized for the production of femtosecond x rays to be installed in
the storage ring.
Undulator
has complete polarization control.
The elliptically polarizing undulator (EPU) in the ALS is now in full user
operation with a high-resolution beamline to provide state-of-the-art
performance. This capability opens up many new experimental possibilities in
polymer, biophysics, and magnetism research all without rotation of the sample.
Upgrades
improve photoemission electron microscopy.
By imaging the photoelectrons emitted from a sample with high spatial
resolution, the photoemission electron microscope is an ideal tool for combining
spectroscopy with variable polarization microscopy in the study of materials
ranging from magnetic materials to polymers.
The performance and sample-preparation facility of this instrument have
been upgraded, making possible new experiments, such as probing the magnetic
roles of the different elements in multilayer structures of the type under
development for magnetic memory and data storage.
A
facility for sub-micron x-ray diffraction developed. Many properties depend on
behavior within individual grains and on the details of grain-to-grain
interactions. The ALS has pioneered the technology needed for x-ray
micro-diffraction and its application to thin-film stress analysis. The system
is capable of measuring structural parameters from grains as small as 0.7
micron. The technique is starting
to play a major role in many materials projects, from stress-induced cracking of
indented high-strength materials to stress in magnetic thin films.
The
Advanced Photon Source (APS) served
1,527 users in FY 2000 by delivering 4,724 operating hours to 34 beam lines at
93.6% reliability (delivered hours/scheduled hours).
The APS is supported by the Materials Sciences subprogram.
3-D
imaging in real time.
A real-time, three-dimensional x-ray microtomography imaging system that
can acquire, reconstruct, and interactively display rendered 3-D images of a
sample at micrometer-scale resolution within minutes has been developed.
This system could bring better understanding of an array of physical
processes, ranging from failure in microelectronic devices to growth and
depletion processes in medical samples.
Novel
x-ray microprobe developed.
The magnetic contribution to the cross section for x-ray scattering is of
significant interest. A technique
has been developed that combines microfocusing x-ray optics with
Bragg-diffracting phase retarders to produce a circularly polarized x-ray
microprobe. This will enable a wide variety of magnetic scattering experiments
in applied fields like magnetic materials and superconducting compounds.
New
beam chopper improves time-resolved experiments. A new beam chopper has
been developed for time-resolved experiments.
The time window of 10 nanoseconds enables time-resolved experiments in
condensed-matter physics, atomic physics, and biological science.
Beam-position
monitor improvements started.
Significant upgrades have been made to the particle beam and x-ray beam
position measurement systems. Further
progress is expected when these changes are incorporated in all of the beamlines
at the APS. This state-of-the-art
improvement in beam stability will provide the APS users with more efficient
beamlines and the capability of working with smaller samples and increased
measurement resolution.
Storage-ring
“top-up” operations developed.
The APS is the first facility to implement "top-up" filling of
the storage with electrons during normal operations.
During 136 hours of top-up operation, the stored current was held
constant to about two parts per thousand by injecting a pulse of electrons once
every two minutes. This resulted in
improvements in x-ray beam stability. Ultimately,
top-up filling will be the routine operating mode of the APS.
Record
FEL SASE achieved.
Using the Low-Energy Undulator Test Line (LEUTL) and the injector linac,
an experimental verification was obtained of the self-amplified spontaneous
emission (SASE) process for 530 nm light. More
recently, saturation of the SASE process at a power level 10,000,000 times
higher than the light produced by a single undulator insertion device was
verified. These experiments are viewed as necessary experimental milestones for
achieving an x-ray free-electron lasers.
The
National Synchrotron Light Source (NSLS) served
2,551 users in FY 2000 by delivering 5,620 operating hours to 90 beam lines at
112.9% reliability (delivered hours/scheduled hours).
The NSLS is supported by the Materials Sciences subprogram and the
Chemical Sciences subprogram.
New
optical polarizer. A newly developed quadruple-reflector optical polarizer
efficiently converts VUV light from linear to either left-circular or
right-circular polarization. This
polarizer expands the capability the U5UA beamline in the area of ultra-thin
magnetic films.
High-resolution
photoelectron spectrometer.
A high resolution photoelectron spectrometer was
installed on the U13UB beamline, and has already produced new physical
insights into the electronic structure of high temperature superconductors.
Infrared
beamlines revitalized.
The 10 year-old infrared microspectrometer at U10B beamline was replaced
with a state-of-the-art continuum microscope and advanced Fourier transform
infrared spectrometer. The system
has been used for the study of interplanetary materials, biological tissues,
corrosion, and materials formed at high pressure. Also, the beam delivery optics for the U12IR beamline were
rebuilt to provide infrared radiation to a new high-resolution spectrometer.
This spectrometer will be used for magnetospectroscopy studies of
materials such as LaMnO3.
Fluorescence
microscopy.
For the first time, an infrared microscope has been modified such that
fluorescence sample visualization and infrared microspectroscopic analysis can
be performed simultaneously. This
unique combination is a valuable analysis tool for probing the chemical
composition of materials.
Advanced
x-ray detector array enables study of trace elements. X-ray
absorption spectroscopy of trace elements in samples poses a serious detection
problem. The detector technology
developed for high-energy physics applications was used to produce a 100-element
energy-resolving detector array for use on an NSLS beamline.
Advanced
x-ray detector system developed.
One of the ways in which diffraction experiments can be made more
efficient is to detect the entire diffraction pattern with high resolution.
In order to accomplish this, a novel curved cylindrical detector was
developed. In addition, a
highly-parallel readout system was developed that is capable of processing
events 10 times faster than before.
Low-cost
monochromator, low-maintence spectrometer. A simple device that
consists of a monolithic silicon diffracting element is near- zero maintenance
and almost adjustment free. It is
now used on five NSLS beamlines; several more such detectors will be installed
at NSLS and at other facilities. The
new device removes need for ultra-fine mechanisms that contribute to most of the
cost of such an instrument and makes x-ray monochromators difficult to control.
Digital
feedback system improves storage ring stability. Meeting the needs of the
large population of NSLS users for high quality photon beams requires an
extremely stable electron orbit. To that end, digital orbit feedback systems to
replace the original analog ones were designed in both the VUV and the X-ray
rings. The main advantage of switching to a digital architecture is the ability
to use a higher number of beam position monitors to achieve a better match
between disturbances on the beam and corrective action by the feedback system.
The digital global orbit feedback system was put into operations in the VUV ring
in August 2000. Implementation of the digital orbit feedback system on the X-ray
ring is expected in FY 2001.
The
Stanford Synchrotron Radiation Laboratory (SSRL) served
895 users in FY 2000 by delivering 4,143 operating hours to 26 beam lines at
96.8% reliability (delivered hours/scheduled hours).
The SSRL is supported by Materials Sciences subprogram and the Chemical
Sciences subprogram.
Reliability
of SPEAR improved.
The reliability of the injector was improved by rebuilding the regulation
of power supplies in the beam transport line.
This contributed to shorter filling times, and, consequently, to longer
beam times available to the users.
Quality
of the photon beam enhanced. Stable
photon beam intensity is one of the requirements for performing demanding
synchrotron radiation experiments. Accelerator
physics studies determined that one type of beam noise was due to the excitation
of high order electro-magnetic modes in the accelerating cavities.
To alleviate this problem, waveguide dampers were installed in the
radio-frequency accelerating system. As
a consequence, SPEAR operates more reliably and the beam stability is improved.
SSRL
beam line systems modernized. Six beam line stations were upgraded to the SSRL
standard data acquisition system and control software. This greatly increases
reliability while reducing user training time, spares requirements, and staff
support requirements.
High
magnetic field x-ray scattering station commissioned.
A new high magnetic field end station incorporating a 13 Tesla
superconducting magnet was constructed and commissioned
on SSRL’s premiere x-ray scattering beam line, BL7-2.
This facility is one of the few facilities in the world that enable
state-of-the-art x-ray scattering experiments in high field environments.
The unique matching of a versatile, high-field magnet with an intense
synchrotron x-ray source allows scientists to unravel the properties of these
new materials. Eventually, the
fundamental understanding that will be derived from this research will lead to
higher performance sensors and magnetic storage devices.
Photoemission
beamline improved for higher throughput and resolution. The
high-resolution angle resolved photoemission beam line station 5-4 has been used
to study the fundamental mechanisms of high temperature superconductivity and
improvements in FY2000 have brought the station to new levels of performance.
The upgrades include a new primary focusing mirror and an angle mode
option to the photoelectron energy analyzer greatly improving throughput.
Molecular
environmental science facility commissioned. The importance of
molecular based research in the environmental area is increasing in importance
due to the emergence problems ranging from environmental remediation at the DOE
weapons labs, to long term storage of nuclear waste, to basic questions
concerning molecular interactions of pollutants at the surfaces of soils.
Beam line station 11-2 has been optimized for x-ray absorption studies of
samples in a variety of states and under dilute field conditions.
The station also includes capabilities for small spot analysis as well as
specialized facilities for the safe handling and analysis of radioactive
materials such as soils contaminated with actinides or wastes from nuclear
storage sites.
New
research and training gateway program initiated.
A Gateway pilot program involving SSRL and the University of Texas at El
Paso (UTEP) is providing training and research opportunities targeted toward
Mexican and Mexican American students. In
FY 2000, a group of 16 UTEP students and staff underwent training and carried
out experiments on four separate
beam lines.
The
Intense Pulsed Neutron Source (IPNS) served
230 users in FY 2000 by delivering 3,842 operating hours to 15 beam lines at
101.6% reliability (delivered hours/scheduled hours).
The IPNS is supported by the Materials Sciences subprogram.
Upgrade
of QENS instrument.
The quasielastic neutron scattering (QENS) instrument was compleely
upgraded. This instrument is used
for measurements that determine the diffusion rates of both molecular rotation
and translation on the typical time-scales of simple liquids, adsorbates etc.
QENS is also capable of measuring vibrational excitations up to a few
hundred meV, providing access to both external and internal vibrational modes
for hydrogenous systems.
IPNS
hosts second National Neutron and X-Ray Scattering School. During the
two-week period of August 14-26, 2000, Argonne National Laboratory once again
hosted the National School on Neutron and X-Ray Scattering.
The success of the previous year was so overwhelming that additional
funds were provided by BES to increase the size of the school from 48 to 60
graduate students. Funding was also
provided by the National Science Foundation.
This school fulfills a continuing need for training graduate students in
the utilization of national user facilities.
The formal program included 32 hours of lectures given by an
internationally known group of scientists recruited from universities, national
laboratories and industry.
The
Manuel Lujan Jr. Neutron Scattering Center at the Los Alamos Neutron Science
Center (LANSCE)
served 25 users in FY 2000 by delivering 736 operating hours to 7 beam lines
at 78.8% reliability (delivered hours/scheduled hours). LANSCE was down for
installation of upgrades and safety shutdowns in FY 2000.
The Lujan Center is supported by the Materials Sciences subprogram.
Neutron
flux increased.
The Lujan Center is the first spallation neutron source to exploit the
increased neutron flux provided by coupled moderators. A new coupled
liquid-hydrogen moderator provides an increase of approximately 2.5 times over
the previous decoupled moderator. Both the small-angle diffractometer, LQD, and
the Surface Profile Analysis Reflectometer, SPEAR, benefits from this increased
flux at Lujan. The increase in flux
is a result of the interaction of the moderator, the reflector surrounding the
moderator, and the lack of decouplers.
The
High Flux Isotope Reactor (HFIR)
served 269 users in FY 2000 by delivering 5,817 operating hours to 12 beam lines
at 92.9% reliability (delivered hours/scheduled hours). The HFIR is supported by
the Materials Sciences subprogram and the Chemical Sciences subprogram.
Cold
source progress.
Work continues on the development of the nation's highest-intensity cold
neutron source. This cold source, which will be comparable in intensity to the
world's best at the Institut Laue–Langevin (ILL) in Grenoble, France, will
support four neutron guides and instruments. The cold source building and
refrigeration plant have been completed, and the guides and cold-source
moderator vessel are in fabrication.
The
Combustion Research Facility (CRF) is
supported by the Chemical Sciences subprogram.
New
capabilities brought on line.
The CRF provides a primary interface for the integration of BES programs
with those of DOE’s Office of Energy Efficiency and Renewable Energy and
Office of Fossil Energy related to combustion by collocating basic and applied
research at one facility. Phase
II of the CRF more than doubled the laboratory floor space to 37,000 square
feet, increasing the number of labs to 37.
The new wing houses unique instruments, such as picosecond lasers for
diagnosing molecular energy transfer. The
turbulent flame diagnostics laboratory, which has become an international
standard, has been expanded to accommodate two simultaneous and independent
experimental stations for visitors. The new laser-imaging laboratory has also been expanded to
include several flame geometries with controlled, reproducible flow structures. New
staff members have been or are being hired in theoretical chemistry, computer
science, and experimental chemical dynamics.
Selected FY 1999 Scientific
Highlights/Accomplishments
Serendipitous Applications of Research in the Physical Sciences to the Life
Sciences.
It has long been recognized that tools and concepts developed in
the physical sciences can revolutionize the life sciences. One need only
consider the impact of x-ray synchrotron radiation and MAD (multiple wavelength
anomalous diffraction) phasing on macromolecular crystallography; both were
developed within the BES program. In FY 1999, many of the annual BES program
highlights illustrate the rapidity with which advances in the physical sciences
are impacting the life sciences. Two examples are given here. First, new
techniques of nuclear magnetic resonance (NMR) are being used to study the
molecular structures of solid protein deposits implicated in brain diseases such
as Alzheimer's Disease and BSE (Mad Cow Disease); both diseases involve the
transformation of normal, soluble proteins in the brain (whose structure is
known) into fibers of insoluble plaque (whose structure is largely unknown).
Second, a nano-laser device has been shown to have the potential to quickly
identify a cell population that has begun the rapid protein synthesis and
mitosis characteristic of cancerous cell proliferation. Pathologists currently
rely on microscopic examination of cell morphology using century-old staining
methods that are labor-intensive, time-consuming, and frequently in error.
Materials
Sciences Subprogram
Seashell Provides Key to Strong Composites. Mollusk shells have
evolved over millions of years to provide hard, strong, tough shelters for
fragile occupants. These outstanding mechanical properties derive from a
laminated construction of alternating layers of biopolymer – a biologically
produced rubber – and calcium carbonate, commonly known as chalk. It has been
recognized for decades that materials with alternating hard and soft layers
absorb energy and impede cracking. Unfortunately, it has proven difficult to
transcribe seashell-like designs into manufacturable materials. Now, a rapid,
efficient self-assembly process has been developed for making
"nanocomposite" materials that mimic the construction of seashells.
This process can be generalized and should lead to materials with unprecedented
mechanical properties.
Imaging Fluid Distribution and Flow in Materials. Dramatic
pictures of the distribution and flow of fluids inside intact objects and porous
solid materials have been obtained by magnetic resonance imaging (MRI) and
nuclear magnetic resonance (NMR). The ability to observe such images and spectra
results from the use of noble gases, particularly xenon, magnetically polarized
by means of a laser. This advance makes possible the observation of MRI pictures
and NMR spectra in ultralow magnetic fields. The technique produces brilliant
pictures (up to a millionfold increase in brightness) and provides a new
capability for noninvasive investigation of flow and transport. The images and
spectra allow the characterization of atomic distribution and flow from the
smallest scale of nanotubes to the largest scale of macroscopic samples. The
flow of fluids through solid materials is a crucial component of many industrial
processes from the catalytic conversion of petroleum to the containment of toxic
environmental agents. These advances will eliminate the need for high magnetic
fields in some applications of MRI and NMR, a welcomed event given the cost,
bulk, hazard, and lack of portability of the magnets used in contemporary
instrumentation.
New Fullerene Species Synthesized - Stickyball, C36. A
new fullerene species, C36, has been synthesized and produced in bulk
quantities for the first time. Fullerenes or "buckyballs" are hollow
clusters of carbon atoms. They have been studied extensively since the Nobel
prize-winning discovery of C60 in 1985 (supported by BES). C36 is
the smallest fullerene discovered to date and is characterized by unusual and
potentially very useful properties. For example, in contrast to C60 molecules,
which interact only very weakly with one another, C36 molecules stick
together – hence the nickname "stickyballs." The lower fullerenes,
such as C36 are predicted to have more highly strained carbon bonds,
resulting in exciting properties for those molecules such as very high chemical
reactivity and high temperature superconductivity. The synthesis of C36 is
particularly significant, because previously it was believed that any fullerene
smaller than C60 would be too unstable to isolate in bulk.
Seeing Clearly Now. Using a new imaging technique called
Z-contrast imaging, researchers have achieved the highest resolution electron
microscope image of a crystal structure ever recorded, resolving adjacent
columns of silicon atoms separated by a scant 0.78 angstroms (3 billionths of an
inch). Better resolution enables scientists to see and understand important
details they had not been able to see before. This technique also offers both
high spatial resolution and the ability to distinguish different kinds of atoms.
The precise atomic-scale structure of a material controls the performance of
materials for semiconductor devices, superconductors, and a host of other
applications. Combined with improved electron imaging optics currently under
development, this result promises to revolutionize the atomic-scale
understanding of materials.
New Family of Bulk Ferromagnetic Metallic Glasses for Energy Efficient
Motors and Transformers. New rules for designing alloys have been
developed that enable the creation of a family of bulk metallic glass alloys.
These alloys exhibit outstanding ferromagnetic behavior with virtually no energy
loss. These new alloys are at least 65 percent iron plus contain up to seven
other elements. Until now, such alloys could only be produced as thin foils.
Commercial transformers based on the thin foil ferromagnetic metallic glasses
are in service, but their size and application are limited due to difficulties
in thin foil assembly and manufacturing processes. The new bulk glasses can be
cast into exact shapes and substituted into the standard assembly processes now
in use for traditional crystalline materials. It is expected that the
availability of bulk ferromagnetic glasses will decrease the energy losses of
transformers by about 2/3 compared to today's transformers made from crystalline
ferromagnetic materials. That's good news for electric utility customers, since
it is estimated that power-distribution transformer losses cost about $4 billion
annually.
Universal Magnetic Behavior in High-Temperature Superconductors.
Understanding high temperature superconductors remains one of the most
significant research issues in condensed matter physics. The observed properties
of two major classes of high temperature superconductors initially appeared to
be significantly different from one other, leading scientists to believe that
the fundamental interactions responsible for the superconducting behavior were
quite different in the two materials. However, recent neutron scattering results
have shown that the superconducting behavior of both major classes of
superconductors is connected to excitations of the magnetic spin system in each
material. The new results offer insight on high-temperature superconductivity
including the promise that a single physical mechanism can account for this
phenomenon.
Chemical Sciences
Subprogram