Highlights from the Materials
Science and
Engineering Laboratory, March 2005
Programmatic/Technical
Accomplishments
Improved Growth
of Zinc Oxide Nanowires
Semiconductor wires just
nanometers across,
known as “nanowires,” show great potential for use in integrated
optoelectronic
and electronic devices including nano-lasers and biochemical detectors.
These
nanowires are often grown in zinc vapor from nanometer-sized molten
metal
islands that are placed on the surface of a substrate of interest.
Researchers
in the Metallurgy Division of MSEL, in collaboration with S. Stranick
of CSTL,
have demonstrated a new “combinatorial” approach for rapidly assessing
a wide
variety of compositions for these metal islands. Patterned wafers with
regions,
or “libraries,” of systematically varying alloys of copper, silver and
gold are
used for simultaneous growth of nanowires under a multitude of
conditions. These experiments demonstrate
nanowire growth
at temperatures substantially below those achievable with conventional
elemental gold islands. The experimental technique also permitted rapid
correlation of the electrical and physical properties of the nanowires
with the
composition of the metal islands from which they were grown. The
results
demonstrate the power of this approach for the control of semiconductor
nanowire properties.
Contact:
Albert
Davydov, x. 4916
NCNR Makes Major Contribution Towards
Standardizing the
Informatics of Powder Diffraction Data
The International Union of
Crystallography
(IUCr) is the professional society that publishes the world’s premier
journals
in crystallography: Acta Crystallographia,
the Journal of Applied Crystallography,
and the Journal of Synchrotron Radiation.
The IUCr has recently begun to require that
all contributing authors submit their crystallographic data and model
fits in a
standardized electronic format known as the Crystallographic
Information
File(CIF) (http://journals.iucr.org/services/cif/powder.html).
In addition, most other journals that publish crystallographic research
have
adopted past IUCr guidelines, so this new change is expected to see
eventual
wide acceptance.
The powder diffraction
component
of CIF is
known as pdCIF (http://www.iucr.org/iucr-top/cif/pd/),
which was developed primarily at the NIST Center
for Neutron
Research. Much of the software now
available for creating and utilizing pdCIF results [Journal of
Applied Crystallography
36, 1285-1287 (2003) and Journal of Applied Crystallography
36,
1290-1294 (2003)] was contributed by the NCNR as well.
Together these standardized formats and
software tools represent a major step forward in the informatics of
powder
diffraction, and will benefit the enormous number of researchers who
use
diffraction techniques, which are the most powerful probes of the
structure of
materials.
CONTACT: Brian
Toby (NCNR), ext. 4297
Interactions
Workshop on Ceramic Armor
Characterization by
Kolsky/Split Hopkinson Pressure bar Testing held at Cocoa
Beach
Ceramics
are rapidly becoming the material of choice for many armor applications
including body armor and vehicular armor.
Despite their effectiveness, there is an urgent need to develop
better,
lower weight armors for the next generation Interceptor body armors and
for the
US Army’s Future Combat System vehicles.
A fundamental understanding of the key material properties
needed for an
effective ceramic armor is lacking, however, and ceramic armor
development to
date has been entirely empirical. There
is some evidence that the key properties may only be revealed by
dynamic
testing. One approach that has
significant potential for identifying key properties is dynamic
compression
testing by the Kolsky/Split Hopkinson Pressure Bar (SHPB) methodology. Unfortunately, differences in test procedures
have caused significant data variability.
Within-laboratory repeatability and between-laboratory
reproducibility
have been poor. NIST has a
Kolsky/SHPB
test apparatus that is operated jointly by MSEL and MEL.
The US Army requested that NIST take a lead
role in improving Kolsky/SHPB testing methodologies.
To that end, NIST Ceramics Division staff
organized and held a special workshop in January in conjunction with a
meeting
of the American Ceramic Society in Cocoa Beach, Florida. Over fifty attendees came, including many of
the world authorities. The state of the
art was reviewed and significant progress was made in identifying areas
where
focused prestandardization research, and perhaps a round robin, could
lead to a
set of testing guidelines.
CONTACT:
George D. Quinn (MSEL), ext. 5765
MSEL
Participates in ISO Working Group Meeting on EPassport Durability
As
indicated in an October 14, 2004, press release from the U.S.
Government
Printing Office (GPO), NIST is testing the candidates for the new U.S.
electronic
passports for their ability to meet durability, security, and
electronic
requirements. This new technology will eventually be incorporated into
electronic U.S.
passports to enhance the security of millions of Americans traveling
around the
world. At the request of the U.S. Department of State, on March 7,
2005,
Polymers Division scientist Walter McDonough participated the WG3
(Working
Group 3 of ISO) meeting of the Document Durability Task Force for the
EPassport
in Tsukuba, Japan.
Also in attendance were officials from the
U.S. Department of State, the U.S. Government Printing Office (the
manufacturer
of the U.S. Passport), and the U.S. Department of Homeland Security. Other attendees were from Japan, Canada,
the European Union and Singapore.
The purpose of the task force meeting was to
update the participants on the status of the Test Specification for
Machine
Readable Travel Documents (MRTD). The main recommendation from the
meeting was
that any proposed test specification by ISO would serve as the
guideline to
help nations writing requests for proposals to develop their own MRTDs. Also, the task force chairs have decided to
use more complex testing sequences to better represent real-world
applications;
this was in line with the recommendations by NIST.
CONTACT:
Walter McDonough (MSEL), ext. 3661; Chad
R. Snyder (MSEL), ext. 4526
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Date created: 5/10/2005
Last updated: 5/10/2005
