Shannon G. Starnes

Energy spectra of electrons and positrons emitted from surfaces as a result of low energy positron bombardment

Abstract Recent measurements of the energy spectra of electrons and positrons emitted from metal and semiconductor surfaces as a result of bombardment with low energy electrons and positrons are reviewed. The high resolution positron re-emission spectra show a close correspondence with that part of the electron induced electron spectrum termed ‘redistributed primaries’ while positron impact-induced secondary electrons show a close correspondence with that part of the electron induced electron spectrum termed ‘true secondaries’. Positron re-emission data from a SiC(0001) surface indicate that this surface has a negative positron workfunction. Peaks in the positron induced electron spectra for Ge(100) and SiC(0001) corresponding to Auger electrons resulting from the annihilation of positrons trapped in a surface state with core electrons in the surface layer are identified and discussed. Additional evidence for the existence of a positron surface state on SiC is provided by data indicating thermal desorption of positronium (Ps).

Positron Annihilation Induced Auger Electron Spectroscopic Studies Of Reconstructed Semiconductor Surfaces

The positron annihilation induced Auger spectrum from GaAs(100) displays six As and three Ga Auger peaks below 110 eV corresponding to M4,5VV, M2M4V, M2,3M4,5M4,5 Auger transitions for As and M2,3M4,5M4,5 Auger transitions for Ga. The integrated Auger peak intensities have been used to obtain experimental annihilation probabilities of surface trapped positrons with As 3p and 3d and Ga 3p core level electrons. PAES data is analyzed by performing calculations of positron surface and bulk states and annihilation characteristics of surface trapped positrons with relevant Ga and As core level electrons for both Ga‐ and As‐rich (100) surfaces of GaAs, ideally terminated, non‐reconstructed and with (2×8), (2×4), and (4×4) reconstructions. The orientation‐dependent variations of the atomic and electron densities associated with reconstructions are found to affect localization of the positron wave function at the surface. Computed positron binding energy, work function, and annihilation characteristics demonstrate...