| When
looking for a needle in a haystack, it's helpful to
know what a needle looks like. A new software tool developed
by researchers at the National Institute of Standards
and Technology (NIST) makes it possible to find chemical
'needles' in data 'haystacks' without having to know
anything about the 'needle' in advance.
The NIST software should be
especially useful for analyzing ultrapure metals--recently
shown to have superior strength, corrosion-resistance
and other properties--and for monitoring nanoscale
semiconductor fabrication. Commercial X-ray detector
manufacturers already have included the method used
in the software into their products.
Described in the November issue
of the Journal of Microscopy*, the software works
with scanning electron microscopes (SEMs) and improves
the analysis of X-ray data. SEMs raster a beam of
electrons across a sample and then detect X-rays emitted
in response. X-rays of specific energies (the equivalent
of colors for visible light) are emitted by specific
elements, making SEMs an excellent tool for mapping
the chemical composition of samples. The lateral and
depth resolutions of SEM/X-ray analysis range from
100 nanometers to 5 micrometers, depending on specimen
composition and SEM beam energy.
Newer detectors---some developed
with NIST funding---respond so fast that data across
the entire spectrum of X-ray energies can be recorded
for every pixel scanned. Typically, these data are
analyzed to show only the sample's major constituents.
The NIST software analyzes the data a step further
by identifying the X-ray energy with the highest intensity
for each pixel rather than for the sample as a whole.
Using the software with a nickel-aluminum sample,
the NIST researchers identified chromium and copper
contaminant particles that occupied just a single
pixel and were not "visible" with the SEM's
usual data interpretation tools.
*D.S. Bright and D.E. Newbury, "Maximum pixel
spectrum: a new tool for detecting and recovering
rare, unanticipated features from spectrum image data
cubes," Journal of Microscopy, Nov. 2004, pp.
186-193
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