Electron Microscopy in Surface Science

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This grant is for renewal of research by Professor John C. H. Spence, Arizona State University, on electron microscopy for study of surfaces of ceramics and electronic materials. During the previous grant (DMR-8512784) more than twelve substantive publications in refereed scientific journals were produced. Highlights of the significant accomplishments include design, construction and testing of a scanning tunnelling microscope which operates inside a transmission electron microscope (allowing simultaneous operation of the two techniques on the same specimen); the technique known as convergent beam electron microdiffraction was made quantitative to allow determination of the electron ground state charge density of gallium arsenide (this allows determination of the nature of the chemical bonds in this technologically important material); advances in theory of electron channeling effect on Auger electron production in the reflection high energy electron diffraction technique provided analytical means to determine the atomic site of adatoms on clean surfaces; a novel method for forming atomic lattice images in semiconductors has been developed which allows lattice imaging of dislocation defects normal to the electron beam with a resolution of 0.3 nanometer (ten times more sensitive than previously possible). The current research will continue to seek novel techniques for the use of electron beams to study the structure of ceramics and electronic materials on a atomic scale with emphasis on the understanding the scanning tunneling microscope, the atom location by channeling-enhanced microanalysis for study of adatoms on semiconductor surfaces; electron energy spectra from surface states; and quantitative electron crystallography for the study of chemical bonding in crystals. Professor Spence has been referred to by his peers as the most innovative scientist using electron microscopy in the U.S. He has consistently trained students of high quality for research in the important field of electron microscopy for materials science.