Channing C. Ahn - US grants

A fundamental investigation of reflection electron energy loss spectroscopy in conjunction with epitaxial growth will be conducted. In situ measurement of core loss ionization and electron energy loss fine structure will be performed during thin film growth by molecular beam epitaxy. These measurements will enable investigation of surface dynamical phenomena during growth, such as surface segregation and relaxation of local order in films at the monolayer level. Of particular interest are the relation etween cation-anion flux ration, surface composition and surface reconstruction for group III-V semiconductor surfaces, and relaxation of local order at group IV(e.g., Si, Ge, Sn) alloy surfaces. Development of a data-parallel ultrahigh vacuum spectrometer will enable increases in data acquisition speed by approximatel;y 2-3 orders of magnitude. %%% This research will investigate a new method for compositional and stuctural analysis of thin films during the actual growth process. Potential benefits include the ability to achieve atomic level control over thin film composition, and semiconductor materials with novel properties and performance for use in advanced electronic and photonic devices and integrated circuits.

Harry Atwater Abstract The acquistion of a quantitative high-resolution video imaging system is proposed. The system will be used in conjunction with existing transmission electron microscopes for (i) atomic-scale imaging of thin films and nanoparticles, (ii) energy-filtered imaging of thin films and nanoparticles, (iii) quantitative electron diffraction nmeasurements,a nd (iv) facilitating the teaching of electron microscopy and microanalyis of materials. ***

This research involves an experimental investigation of the thermodynamics of nanophase materials. Mechanical attriting is the technique employed to process various nanophase metallic systems. Associated effects of environmental factors during attriting are determined. Both positive and negative heats of mixing are represented in the materials' systems proposed. Grain boundary segregation tendencies are noted and related to the potential for grain growth during low temperature annealing and consolidation. Several experimental characterization methods are proposed to examine the chemistry on a nanoscale, including calorimetry, electron energy loss spectrometry (EELS), Mossbauer spectrometry, and small angle X-ray scattering (SAXS). %%% Nanostructured materials are a class of new materials whose properties are expected to be markedly changed by the consequences of the fine structure. This research explores factors affecting the stability of such materials.