Etching and a disordered overlayer on the Ge 100/-S surface

High resolution core level photoelectron spectroscopy PES.and scanning tunneling microscopy STM.have been used to study the adsorption and desorption of S on and off the Ge 100.surface. The previously proposed bridge adsorption site of S is consistent with our results at low coverage. At saturation the substrate contains several GeSx species, with xs0.5 to 4. Both photoemission and STM reveals a non-ideal surface, with a saturation coverage above one monolayer. Furthermore, S is found to etch the substrate. The reaction products forms a disordered overlayer on top of the interface. This overlayer is transparent in the filled state STM images