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

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).