Electron stimulated desorption of negative ions has been investigated
with SiCl4 adsorbed at Si(100). Cl- ion is the only negatively charged
species detected and the ion yield peaks at 1 ML coverage when SiCl4
is adsorbed at a clean Si(100) surface. The higher ion yield from the
first monolayer of SiCl4 is interpreted as due to charge transfer from
the surface to the lowest unoccupied level of SiCl4, in association w
ith an enhanced symmetry change from T-d to C-3v.