X-ray standing wave surface studies in ultra-high vacuum: Chromium on germanium and lithium bromide on silicon
Abstract
As a precursor to x-ray standing wave studies using electron detection as a surface probe, an investigation of the Si L$\sb{23}$VV Auger line shape for a Si(111) surface before and after deposition of a sub-monolayer of Ge was conducted. It is found that Si atoms in the topmost layer have a qualitatively different line shape than atoms in lower lying layers. In particular, the redistribution of electron density at the Si surface enhances the contribution of $sp$ Auger transitions while suppressing $pp$ transitions. This surface effect is expected to be a general property of LVV spectra from all surfaces. A laboratory-based x-ray standing wave study of Cr on a Ge(111) surface under UHV conditions was performed. Measured coherent positions and coherent fraction point towards an interface involving Cr-Ge intermixing. In particular, a model of a CrGe/Ge interface is found to be consistent with measured results and constitutes one possible surface structure for the Cr/Ge system. A synchrotron x-ray standing wave experiment of LiBr on Si(111) in UHV was also conducted. For three different surface preparations the coherent positions and coherent fractions are found to be 0.63, 0.11; 0.74, 0.14; 0.84,.038 respectively. The first and third coherent positions are consistent with adsorption sites observed in earlier experiments on elemental Br on Si(111). No information could be gained on the position of Li ions.
Degree
Ph.D.
Advisors
Durbin, Purdue University.
Subject Area
Condensation
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