Photoionization and Photoemission by the Standing - Intensity of Dynamical X-Ray Diffraction.

This thesis contains theoretical studies of nonrelativistic, inner-shell photoionization, and angle-resolved, photoelectron ejection by the standing-wave intensity of dynamical x -ray diffraction in the Bragg reflection geometry. These studies are carried out for two purposes: (1) to put the yield formulae of the X-Ray Standing Wave Technique (XSWT) in the differential form most appropriate for the application of photoelectron spectroscopy, and (2) to answer a lingering question on the adequacy of the dipole approximation for describing the photoeffect spectra of XSWT via investigating the effects of quadrupole retardation on the determination of the coherent fraction and the coherent position. In the dipole approximation, electron photoejection by the standing-wave intensity of XSWT has been found to differ from corresponding fluorescence and Auger emissions in that it proceeds at rate not proportional to the standing -wave intensity unless the dynamical diffraction field is in the sigma polarization geometry, or otherwise the XSWT experiment is performed at small Bragg angles or near-normal incidence conditions. It has also been found that the coherent position is by no means sensitive to effects owing to quadrupole retardation, whereas numerical results calculated for a Si adsorbate on a Ge substrate have exhibited changes exceeding 10% in the magnitude of the coherent fraction, but only for unfavorable experimental conditions. This observation has led to concluding the dipole approximation sound and accurate for most practical XSWT experiments.