| Sept.
9, 2005
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New
Material May Have ‘Liquid’ Magnetic State
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A
crystal diagram shows the triangle-shaped atomic structure
of nickel gallium sulfide, which may have an unusual
magnetic "liquid" state at low temperatures.
Red spheres represent nickel, green spheres are gallium,
and yellow are sulfur.
Image
credit: S. Nakatsuji et al., Science, 9/9/2005
View
high-resolution version of image |
A novel
material that may demonstrate a highly unusual “liquid” magnetic
state at extremely low temperatures has been discovered by
a team of Japanese and U.S. researchers, according to the Sept.
9 issue of Science.*
The material,
nickel gallium sulfide (NiGa2S4), was synthesized by scientists
at Kyoto University. Its properties
were studied
by both the Japanese team and by researchers from The Johns
Hopkins University (JHU) and the University of Maryland (UM)
at the Commerce Department’s National Institute of Standards
and Technology (NIST).
The scientists
studied the polycrystalline sample using both X-rays and
neutrons as probes to understand
its structure and
properties. The neutron experiments were conducted at the
NIST Center for Neutron Research.
The
team found that the triangular arrangement of the material’s
atoms appears to prevent alignment of magnetic “spins,” the
characteristic of electrons that produces magnetism. A “liquid” magnetic
state occurs when magnetic spins fluctuate in a disorderedly,
fluid-like arrangement that
does not produce an overall magnetic force. The state was first proposed
as theoretically possible about 30 years ago. A liquid magnetic
state may be related to the similarly
fluid way that electrons flow without resistance in superconducting materials.
According
to Collin Broholm, a professor in the Department of Physics
and Astronomy at The Johns Hopkins University in Baltimore, “the
current work shows that at an instant in time the material
looks like a magnetic liquid, but whether
there are fluctuations in time, as in a liquid, remains to be seen.”
The
team conducted their neutron experiments with an instrument called
a “disk
chopper spectrometer.” The only one of its kind in North America,
the instrument sends bursts of neutrons of the same wavelength through
a sample. Then, more
than 900 detectors arranged in a large semicircle determine exactly where
and when the neutrons emerge, providing information key to mapping electron
spins.
For further
information, see:
www.nist.gov/public_affairs/releases/magnetic_liquid.htm.
*
S. Nakatsuji, Y. Nambu, H. Tonomura, O. Sakai, S. Jonas, C. Broholm,
H. Tsunetsugu, Y. Qiu, Y. Maeno, "Spin disorder on a triangular
lattice." Science, Sept. 9, 2005.
A
New Structural View of Organic Electronic Devices
Although
still in the qualifying rounds, U.S. researchers are helping
manufacturers win the race to develop low-cost ways to commercialize
a multitude of products based on inexpensive organic electronic
materials—from large solar-power arrays to electronic
newspapers that can be bent and folded.
In
the on-line issue of Advanced Materials,* researchers
from the National Institute of Standards and Technology
(NIST) and the University of California at Berkeley report
success in using a non-destructive measurement method to
detail three structural properties crucial to making reliable
electronic devices with thin films of the carbon-rich (organic)
semiconductors. The new capability could help industry clear
hurdles responsible for high manufacturing development costs
that stand in the way of widespread commercial application
of the materials.
With
the technique called near-edge X-ray absorption fine-structure
spectroscopy, or NEXAFS, the team tracked chemical reactions,
molecular reordering and defect formation over a range of
processing temperatures.
They
then evaluated how process-induced changes in thin-film
composition and structure affected the movement of
charge carriers (either electrons or electron “holes”)
in organic field effect transistors, devices basic to electronic circuits.
With NEXAFS measurements taken over the range from
room temperature to 300 degrees
Celsius, the team monitored the conversion of a precursor chemical to an
oligothiophene, an organic semiconductor. The molecular
organization and composition achieved
at 250 degrees Celsius yielded the highest levels of charge carrier movement
and, consequently, maximum electric-current flow.
As
chemical conversion progressed, the researchers calculated how the molecules
arranged themselves
on top of an electrical insulator. Top transistor
performance
corresponded to a vertical alignment of molecules. In addition, they
used NEXAFS to determine the angles of chemical bonds
and to assess the thickness
and uniformity
of film coverage, also critical to performance.
NEXAFS
has the potential to be the “ideal measurement
platform for systematic investigation” of organic
electronic materials, says lead investigator Dean DeLongchamp,
a NIST materials scientist. “A straightforward
means of correlating chemical and physical structure
to the electronic performance
of organic semiconductor films is a much-needed tool.”
The
research was conducted at the NIST/Dow Chemical materials
characterization facility at the National Synchrotron Light
Source. Funding providers included the U.S. Department of
Energy, Defense Advanced Research Projects Agency and the
Microelectronics Advanced Research Corporation.
*D.M.
DeLongchamp, S. Sambasivan, D.A. Fischer, E.K. Lin, P. Chang,
A.R. Murphy, J.M.J. Frechet, and V. Subramanian, “Direct
Correlation of Organic semiconductor film structure to field-effect
mobility,” Advanced Materials, published
online Aug. 30, 2005, DOI number (10.1002/adma.200500253).
Media
Contact:
Mark
Bello, mark.bello@nist.gov,
(301) 975-3776
NIST
Shielding Data Help Launch Shuttle
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NIST
researchers Dennis Camell (left), Chriss Grosvenor
(on the ground), and Nino Canales assemble an antenna
tower used in the NIST system for measuring the space
shuttle's electromagnetic shielding.
Image
credit: Photo by David Novotny/NIST
View
high-resolution version of image |
As
the National Aeronautics and Space Administration (NASA) plans
for the next launch of the space shuttle, a critical aspect
of the program's safety is being assured by 5 million pieces
of data collected recently by the National Institute of Standards
and Technology (NIST).
To help prevent a repeat of the 2003 accident when launch
debris damaged the shuttle Columbia, causing it to break up
on re-entry, NASA has begun illuminating shuttles with tracking
radars during launches and ascent to detect and quantify potential
hazards. Concerns about possible disruption of onboard electronic
guidance and control systems led NASA to request NIST's help
in determining how much radar energy can penetrate the orbiter
in key locations.
During
the launch of Discovery in July, radar was used to track
debris during ascent and NASA considered the NIST shielding
data vital to the resumption of shuttle flights.
NIST has
been conducting research in this area for several years and
has developed a portable system that efficiently measures the
electromagnetic shielding characteristics of airframes. The
systempreviously has been used to evaluate both commercial and
military aircraft. NIST engineers visited the Kennedy Space
Center in Florida to evaluate the space shuttle Endeavor and
the hanger in which the measurements were made.
The NIST
system incorporates ultra-wideband antennas, a precision
optical link between them, and a computerized data analysis
system. The two-step measurement process consisted of a reference
measurement with the transmitting and receiving antennas outside
the shuttle, and a penetration measurement with the receiving
antennas at selected locations inside the orbiter. A computerized
comparison of these two measurements over specific time periods
and frequency bands provided a measure of shielding characteristics
in the frequency range 30 megahertz to 6 gigahertz. The data
enabled NASA to set safe power levels on radar systems used
to detect debris.
Comments
Sought on Revision of Federal ID Standard
The
National Institute of Standards and Technology would like
comments on proposed changes to a Federal Information Processing
Standard (FIPS) issued in February for a smart-card-based
form of identification for all federal government departments
and agencies. The proposed changes to FIPS 201, Standard
for Personal Identity Verification of Federal Employees
and Contractors, will make it consistent with guidance issued
on Aug. 5, 2005, by the Office of Management and Budget
(see M-05-24 www.whitehouse.gov/omb/memoranda/index.html#2005)
concerning the identity proofing and registration process
that departments and agencies should follow when issuing
identification credentials.
In short, under the proposed FIPS revision, if an agency
does not receive the results of a background check known
as the National Agency Check (NAC) within five days, the
identification credential can be issued based on the FBI
National Criminal History Check. Information stored electronically
on the identification credentials issued to individuals
without a completed NAC or equivalent must be distinguishable
from that issued to individuals who have a completed investigation.
The proposed changes to FIPS 201 are available at http://csrc.nist.gov/publications.
Comments concerning the proposed changes should be sent
to fips.comments@nist.gov or Information Technology Laboratory,
ATTN: Proposed Changes to FIPS 201, Mail Stop 8930, National
Institute of Standards and Technology, 100 Bureau Drive,
Gaithersburg, MD 20899. Comments must be received by Oct.
11, 2005.
More information on FIPS 201 and the personal identity
verification program is available at http://csrc.nist.gov/piv-program/index.html
Media
Contact:
Jan
Kosko, kosko@nist.gov, (301) 975-2767
Quick
Links
Experts
To Examine Virtual Enterprise Uses of Info Tech
The
National Institute of Standards and Technology (NIST)
and Enterprise Integration Inc. (EII) are sponsoring
a conference on how computer programs for business
models, modeling and simulation methodologies, and
automation tools and technology can be used in consort
to offer manufacturing enterprises a competitive advantage.
Participants in the “IFIP 5.7 Advances
in Production Management Systems: Modeling and Implementing
the Integrated Enterprises” conference,
to be held Sept. 19-21 in Rockville, Md., will look
at the role of integrated computer production and
control systems in such activities as “building
inventory transparency,” “global sourcing”
and developing “frameworks for enterprise modeling.”
The September meeting should be of particular interest
to industry and academic researchers interested in
the latest advances in computer applications to industrial
engineering, business administration, management and
systems operations.
The
conference is associated with the International Federation
on Information Processing and its 5.7 working group
on the use of computer systems in production management.
For further conference information and to register
online, go to www.apms2005.org/index.html.
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