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 e mitted from metal and semiconductor surfaces as a result of bombardmen t with low energy electrons and positrons are reviewed. The high resol ution positron re-emission spectra show a close correspondence with th at part of the electron induced electron spectrum termed 'redistribute d primaries' while positron impact-induced secondary electrons show a close correspondence with that part of the electron induced electron s pectrum termed 'true secondaries'. Positron re-emission data from a Si C(0001) surface indicate that this surface has a negative positron wor kfunction, Peaks in the positron induced electron spectra for Ge(100) and SiC(0001) corresponding to Auger electrons resulting from the anni hilation of positrons trapped in a surface state with core electrons i n the surface layer are identified and discussed, Additional evidence for the existence of a positron surface state on SiC is provided by da ta indicating thermal desorption of positronium (Ps).