AMPSIES: A new top-layer selective positron induced electron spectroscopy for studying the surface electronic structure of materials.

Research at the University of Texas at Arlington’s positron lab has led to the first observations of a positron induced low energy electron emission mechanism, termed Auger mediated positron sticking (AMPS). AMPS is initiated by the energy transfer associated with the positron’s transition from a scattering state to a surface bound state. Recent theoretical investigations of the AMPS mechanism have revealed that the emission process is sensitive to surface localized valence electron states near the Fermi level, with minimum contamination from bulk electronic states. This surface selectivity is due to the highly localized character of the screened Columbic potential. A model based on the valence density of states near the Fermi level, the unoccupied density of states above the vacuum level, and the escape probability of emitted electrons has been shown to successfully reproduce the line shape of the AMPS peak for several materials. Therefore, the AMPS mechanism offers a new type of surface selective positron induced electron spectroscopy, which we have termed, AMPS induced electron spectroscopy (AMPSIES). In this report, we present AMPSIES measurements on Cu, Si, and HOPG and their simulated line shapes.