High-resolution inverted x-ray photoelectron diffraction studies of Si(100)

Abstract

An inversion of the x-ray photoelectron diffraction (XPD) experiment has been performed in which incident electrons are diffracted to reach different sites within a crystal with differing relative probabilities reflecting those for escape of photoelectrons from the same sites in the corresponding XPD experiment. The diffracted-electron flux arriving at each site was monitored by using a Si(Li) detector to measure the intensity of the characteristic x-ray emission following core ionization by the incident electrons. This new technique, termed `inverted' x-ray photoelectron diffraction (iXPD), has been initially applied to Si(100) for rotation about , and the expected close parallels between XPD and iXPD data have been observed. Although the intensity of the x-ray signal increased rapidly as the incident-beam energy was increased beyond the threshold value for core ionization, the extent of the angular anisotropy correspondingly decreased, and there was little advantage in terms of signal:noise ratio in the iXPD pattern in increasing the energy to more than 10 - 15 eV above the threshold. The reduction in anisotropy resulted from a progressive degradation of the directional integrity of the electron beam by inelastic energy-loss processes. The angular resolution in iXPD is governed by the incident-beam divergence, which can easily be as small as , much less than the angular acceptance of typical electron energy analysers. High-resolution iXPD data taken above the threshold showed up to 38% angular anisotropy, much more than for conventional XPD at angular resolution, while iXPD data taken as much as 15 - 30 eV above the threshold still revealed splittings of all of the principal forward-scattering maxima of . Similar splittings have been reported for high-resolution XPD of other systems, but not for Si(100). Their origins are briefly discussed.