~,rface Scmnce 269/270 (1992) 573-576 North-Holland ", ,,,, "surface sc{encg Radiative capture of near zero kinetic energy electrons by solids S.N. Samarin lnstttute of Phystcs, Lemn~rad State Uhtt,erstt~, Ulianot,skaya 1, Petrodtoretz, St. Petersburg 1989~4, Russia Recewed 23 August 1991; accepted for pubhcatton 13 January 1992 Radmtwe capture (reverse photoemisston)of near zero kmettcenergy electrons by metal surfaces was investigated It was shown that electron affinityof surfaces, mean free path of near zero energy electrons in Ag and metal to semiconductortransltton can be stu&ed using the radiative capture of Iow-energ, electrons b, sohd surface. 1. Introduction Methods based on radiaSve capture of elec- trons by solids (inverse phatoemission) are now :he most effective tool for studying unoccupied electron states in a soV, [i]. Almost all experimental studies of ra&atwe capture of electrons (RCE) by solids we,e per- formed at the energy of detected photons hoJ > 9 eV [1]. The electron energy threshold E~ for emission of photons of energy hop is determined b',' equ~t,nn: E t = hto- ex, ~ i ) where ex is the electron affinity of a sample surface (fig. 1). That means that for the investi- gated metals (ex = 3-5 eV) the electron energy threshold E I is determined by an inequality: E t > 9 - 5 = 4 eV. (2) ........ L.,,J= CF Fig 1 Ene,getlc dtagram of RCE for low-energyelectrons So, radiative captme of near zero kmettc en- ergy electrons by solids was never observed. Meanwhile, to observe this phenomenon for elec- tron energy E --- 0 is of indubitable interest. This interest comes from: (1) The mean free path of such electrons is large ~50 ~.) and the probability of RCE by solids is high [2] (2) The expansion of the energy range of the incident electron energy in RCE leads to obtam- mg more mformrtion about empty electron states in solids. Fm example, ~t ~s well known that the cross section of RCE ~o final sta~es of different symmetry " °" ' ..a ~s,p,fl,i, ucpc,,.~s on the incident elec- tron energy [3]. (3) The radiation accompanying the capture of very low kinetic energy electrons by solids is one of very few electron-solid interaction manifesta- tions at such low electron energy. Accordingly, this radtative phenomenon can be used not only to investigate empty states in sohds, but also to study electron scattering in this energy range. (4) An electron entering the sohd m the prox- irony of the top of o~Jrface barrier ts very sensnRve t~ ~t~ ~hapc. To investigate the radiat,ve capture of near zero energy electrons by sohds it is necessary, to detect photons of energy ~<ex, where eg is the affinity of the sohd (fig. 1}. This means that the enmgy of detected photohs must be of the order of a few electron-volts (3-6 eV). 003%6028/92/$05 00 © 1992 - Elsevier Sctcncc Pabhshers B ~/ ARI ra~hts ~cscrvcd