THEORETICAL-STUDY OF THE APPLICATION OF POSITRON-INDUCED AUGER-ELECTRON SPECTROSCOPY

The interpretation and prospective applications of the novel surface-science technique positron-induced Auger-electron spectroscopy (PAES) have been investigated theoretically by calculations of annihilation rates of surface-trapped positrons with core electrons. The positron surface state is described by the corrugated-mirror model and core-annihilation rates are calculated with use of the independent-particle model. At clean surfaces of Al, Ni, Cu, and Au, 15 % of surface-trapped positrons are found to annihilate with core electrons and thus give rise to Auger-electron emission. On low-Miller-index surfaces more than 80% of the core annihilations take place with electrons from the topmost layer of atoms, which demonstrates the extreme surface sensitivity of PAES. Adsorption of impurities is found to reduce the substrate Auger signals, and the intensity of Auger lines due to the adsorbate increases with increasing coverage in agreement with recent experiments by Mehl et al. The results are found to depend markedly on whether the adsorbate atoms occupy subsurface sites or chemisorption sites above the surface, demonstrating that PAES can be useful in studies of adsorbate location. The applicability of PAES to studies of alloy surfaces and surface segregation is illustrated by calculations for Cu-Au surfaces. A set of bulk positron calculations shows that most elements are expected to have strong PAES signals. © 1990 The American Physical Society.