Electron capture from occupied surface states within the band gap of LiF(100)

Measurements of scattered neutral fractions for Na, K, and Cs multicharged ions grazingly incident on Li(100) as function of projectile velocity suggest that near resonant processes are active in the final neutral formation, involving occupied surface states within the band gap of the alkali halide target. Observed scattered negative fractions for incident 0, F. and B projectiles are consistent with such a scenario as well. A model treatment of the projectile charge fraction velocity dependence is utilized to deduce from the experimental data a work function and Fermi energy of 3.8 eV and 0.8 eV, respectively, for this surface band. Measurement of the parallel velocity dependence of the image charge acceleration of Ne{sup 6+} grazingly incident on LiF(100) in the range 0.1 - 0.52 a.u. are shown to provide further support for the presence of a band of surface states having the above parameters.