Media
Contact:
Michael
E. Newman, (301) 975-3025
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Information Technology
Pervasive
Computing Conference Adds Health Care Track
With
the use of mobile devices such as personal digital assistants (PDAs)
becoming more widespread, pervasive computing—the convergence
of computers, wireless systems, sensors that “see” and
“hear,” and the Internet so that people use their machines
in a natural, unobtrusive way—is finding greater application
in the workplace and the home. Software is becoming increasingly
adept at handling device and service discovery, while mobility middleware
is becoming more sophisticated. The upcoming Pervasive Computing
2002, the third annual conference in a series hosted by the National
Institute of Standards and Technology (NIST), will provide researchers,
developers and users with a forum to discuss “state-of-the-art”
in the field.
Scheduled
for Oct. 1-2, 2002, the conference will cover a wide variety of
technical topics, with presentations on PDAs, computing platforms,
security, standards and smartcards by technology experts from industry
and academia. This year’s program adds a special health care
track designed to facilitate an exchange between medical practitioners
and technology developers. As a way of cutting costs and increasing
operating efficiencies, the health care community has begun to take
advantage of the advances in pervasive computing. These technologies
also are increasingly being applied to medical diagnosis and treatment.
The
conference will be held at NIST’s headquarters in Gaithersburg,
Md. More information, including a conference agenda and online registration
form, may be found at www.nist.gov/pc2002.
Media
Contact:
Philip
Bulman, (301) 975-5661
Semiconductors
NIST Image Library
to Help Improve Linewidth Measurements
Imagine
trying to make absolutely critical measurements for semiconductors
using instruments that do not quite measure up. That’s the challenge
currently faced by those needing accurate measurements of the “critical
dimension” or CD—the smallest size that can be etched onto
a computer chip uniformly. In the semiconductor industry, CD is synonomous
with the measure of linewidth.
Linewidths
are generally determined using an image generated by an instrument
such as a scanning electron microscope (SEM). The pattern of light
and dark in an image results from a complex interplay between the
microscope and the sample’s shape, composition and other properties.
Unfortunately,
lines with different sidewall geometries appear to have different
widths when measured using algorithms that are standard on current
CD-SEMs. In other words, sidewall variation masquerades as width variation,
yielding an inaccurate measurement.
To
help resolve the situation, the National Institute of Standards and
Technology (NIST) is developing a method of determining linewidth
and lineshape from a library of top-down SEM images (the top-down
measure is widely used.
NIST’s
new method explicitly accounts for the physics of the interaction
of the SEM’s electron beam with the sample as well as the effect
of sidewall geometry. The approach entails performing calculations
in advance for many different shapes to learn what images will be
produced—information that can be used to form a library, or database,
of actual sample shapes and calculated image pairs.
To
determine the shape of an unknown sample, its measured image is compared
to computed images in the database to locate the closest match. When
the measured image lies between two library images, the best parameters
are interpolated.
Unlike
scatterometry, where measurements are averaged over a relatively large
target, the NIST technique relies on an SEM’s higher resolution
to yield a more localized measurement.
In
early tests, NIST researchers have compared measurements using this
method to cross sections of the same lines. Agreement for linewidth
was within one or two nanometers, and within one- or two-tenths of
a degree for wall angles. Measurement repeatability also was significantly
greater than with current methods.
NIST
expects to deliver stand-alone software that incorporates these calculations
to International SEMATECH by the end of the year.
For
more information, contact John Villarrubia, (301) 975-3958, john.villarrubia@nist.gov.
Media
Contact:
Philip
Bulman, (301) 975-5661
Neutron Research
‘Frustrated
Magnets’ Hint at Nature’s Powers of Organization
When
“frustrated” by their arrangement, magnetic atoms surrender
their individuality, stop competing with their neighbors and then
practice a group version of spin control—acting collectively
to achieve local mag-netic order—according to scientists from
the National Institute of Standards and Technology (NIST), Johns Hopkins
University and Rutgers University writing in the Aug. 22, 2002, issue
of the journal Nature.
The unexpected
composite behavior detected in experiments done at the NIST Center
for Neutron Research (NCNR) accounts for the range of surprising—and,
heretofore, unexplainable—properties of so-called geometrically
frustrated magnets, the subject of intensifying research efforts that
may lead to new types of matter. The finding also may shed light on
natural clustering processes including the assembly of quarks and
other minuscule components into atoms, the folding of proteins and
the clumping of stars in galaxies.
The team discovered
that self-organized “spin clusters” emerge out of competing
interactions in a geometrically frustrated magnet. Though involving
interactions on a nanometer scale, the discovery may provide a new
model for exploring “emergent structure in complex interacting
systems” on different levels.
The researchers
set out to determine how atoms arrayed in the lattice-like geometry
of frustrated magnets resolve an apparent predicament: how to align
their spins—the sources of magnetism—when faced with a bewildering
number of options.
As a conventional
magnet cools, atoms pair up with their neighbors and line up their
spins, so that they spin in parallel or in opposition (antiparallel).
At a temperature unique to the type of material, the magnet undergoes
a phase transition and achieves a highly symmetrical, long-range ordering
of spins. The material and each spin are said to be in their ground
state, a condition of equilibrium, or ultimate stability.
This is not the
case for a geometrically frus-trated magnet, which is assembled from
triangular units. If atoms at two corners spin antiparallel, the atom
in the third is left with a no-win situation. Whichever orientation
it chooses, the third atom will be out of sync with one of its two
neighbors. As a result, the entire system is “geometrically frustrated”
and all spins can fluctuate among a range of potential ground states.
The paper “Emergent
excitations in a geometrically frustrated magnet” appears in
Nature, Volume 418, pages 856-858 (Aug. 22, 2002) and may be
accessed at www.nature.com.
Media Contact:
Mark
Bello, (301) 975-3776
