Positron probes of the Ge(1 0 0) surface: The effects of surface reconstructions and electron–positron correlations on positron trapping and annihilation characteristics

Abstract

Positron annihilation induced Auger electron spectroscopy (PAES) has been applied to study the Ge(100) surface. The high-resolution PAES spectrum from the Ge(100) surface displays several strong Auger peaks corresponding to M4,5N1N2,3, M2,3M4,5M4,5, M2,3M4,5V and M1M4,5M4,5 Auger transitions. The integrated peak intensities of Auger transitions are used to obtain experimental annihilation probabilities for the Ge 3d and 3p core level electrons. These experimental results are analyzed by performing calculations of positron surface states and annihilation characteristics of surface trapped positrons with relevant Ge core-level electrons for the non-reconstructed and reconstructed Ge(100)-p(2×1), Ge(100)-p(2×2) and Ge(100)-c(4×2) surfaces. It is found that the positron surface state wave function extends into the Ge lattice in the regions where atoms are displaced from their ideal terminated positions due to reconstructions. Estimates of the positron binding energy and the positron annihilation characteristics reveal their sensitivity to the specific atomic structure of the topmost layers of Ge(100). A comparison with PAES data reveals an agreement with theoretical core annihilation probabilities for the Auger transitions considered.