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Surface and Microanalysis Science Atmospheric and Chemometric Research |
Surface and Microanalysis Science Division Contact: Richard Cavanagh The macroscopic properties and behavior of a wide variety of physical, biological, and technological phenomena are controlled by chemical events that occur on the microscale. Microbeam analysis techniques based on beams of electrons, ions, and photons can achieve lateral and depth resolution ranging from the micrometer to the nanometer scale, which is equivalent to a sample mass of picograms down to zeptograms. We perform research in many aspects of the measurement science of microbeam analysis. We develop standards, data, and standard methods to meet the critical need for chemical measurements that can provide quantitative information on small variations in composition or structure. We study trace constituents through techniques that can achieve trace nanoanalysis, which combines trace fractional sensitivity with nanometer-scale resolution. Measurement of the atoms present in a microstructure is complemented by techniques that determine the molecular forms present as well as the arrangement of atoms and molecules into crystallographic forms. The need to visualize lateral compositional distributions quantitatively has been the subject of an extensive effort to develop compositional mapping in which the result is in the form of an image where the gray or color level is directly related to numerical concentration. Initially developed for picture elements (pixels) in two lateral dimensions, current efforts seek to extend compositional mapping to three-dimensional volume elements and hyperspectral imaging, a capability needed to meet the challenges posed by advanced technologies such as giga-scale electronics, combinatorial chemistry, and microelectromechanical systems (MEMS). We have instrument
resources and measurement expertise including scanning electron microscopy
(conventional, electron probe X-ray microanalysis, environmental, field
emission, and Auger), high-voltage transmission analytical electron microscopy
(conventional and field emission, with X-ray and electron energy loss
analytical spectrometries and energy filtered imaging), and secondary
ion mass spectrometry (ion microprobe, ion microscope, and laser microprobe
with magnetic sector or time-of-flight mass spectrometers). Also available
are conventional and Fourier-transform Raman optical microprobes; Fourier-transform
infrared microscopy; X-ray diffraction and fluorescence, including capillary
optic X-ray microfocusing facilities from conventional X-ray tubes, high-brightness
rotating anode X-ray sources, and beamlines at national synchrotron facilities;
and extensive facilities for computer-aided microscopy and analysis, sample
synthesis, and sample preparation including facilities for manufacture
of compositional glass reference materials and thin specimen preparation. Contact: David S. Simons or Eric B. Steel Atmospheric and Chemometric Research Concern is mounting worldwide over atmospheric pollution and potential effects on health and climate. It is imperative to determine with a high degree of accuracy the individual sources of pollutant species, whether they are local or remote, and natural or manmade. State-of-the-art research, pioneered at NIST, makes possible unique source identification by application of the most advanced microchemical and isotopic analytical techniques, including accelerator mass spectrometry and high-precision gas isotope ratio mass spectrometry. The data obtained provide federal, state, and city governments with a unique opportunity to develop and test control strategies to reduce emissions from the identified pollutant sources. Additionally, we develop reference materials and data for national and international measurement communities to provide the highest traceability of measurements to primary standards. Complementing advanced
isotopic-chemical characterization of atmospheric gases and particles
is our basic research in chemometrics, which represents the synthesis
of chemical knowledge and measurement with modern statistical and computational
methods. Work in this area is directed toward improving the quality of
chemical measurements generally through advanced design, measurement and
data analysis, quality assurance, and graphical multivariate data exploration. Contact: R. Michael Verkouteren Surface and Interface Research Understanding the processes that occur at surfaces and interfaces, such as the interactions of adsorbates with substrates, is critical for describing and controlling reactions at these locations. This understanding can lead to new procedures that are fundamental in tailoring surfaces to produce nanoscale structures, decrease wear and corrosion, or to develop new electronic devices, catalysts, or layered materials with improved properties. To address these
important technological areas, we are utilizing laser-based far-field
and scanning near-field probes, as well as charged particle-based diagnostics,
to study the fundamental, atomic-scale processes that occur for a broad
spectrum of surface and interface systems. We apply these techniques to
a wide variety of substrates, including metals, semiconductors, and oxides,
as well as thin-film systems composed of polymers, oxides, and biomimetic
materials. This research provides critical information on the electronic
structure, topography, chemical reactivity, and the mechanisms of energy
transfer at surfaces and interfaces. In addition to these experimental
techniques, we develop theories and analytic procedures that pull together
diverse ideas to provide comprehensive, focused explanations of the processes,
which, in turn, lead to new experimental designs and research. Contact: Steven A. Buntin
Date
created:
September 28, 2001 |