Trajectory dependence of scattered Ne+ and recoiled S- ion fractions from the Cd- and S-terminated CdS{0001} surfaces

Scattered Ne+ and recoiled S- ion fractions resulting from 4 keV Ne+ and 4 keV Kr+ impingement, respectively, on both the Cd- and S-terminated surface s of CdS{0001} have been measured. The absolute values of these ion fractio ns as well as their dependence on surface structure and electron density ha ve been determined. Using a density functional approach, a clear correlatio n has been demonstrated between these Ne+ and S- ion fractions and the late ral variation of the electrostatic potential along the outgoing trajectorie s of the scattered and recoiled atoms. The observed anisotropy in the ion f ractions is a result of the variations in surface to atom electron transfer rates due to tunneling barriers introduced by the electrostatic potentials . Both the Ne+ and S- ion fractions are higher on the Cd-terminated surface than on the S-terminated surface and their azimuthal patterns are differen t due to the spatial modulation of the electron tunneling rates on the surf ace caused by the electrostatic barriers. The azimuthal anisotropies of ele ctrons ejected during the collision indicate that they are emitted only fro m collisions whose impact parameters are less than a threshold value, consi stent with a kinetic electron emission mechanism. (C) 1999 American Institu te of Physics. [S0021-9606(99)70116-9].