Local state density and long-range screening of adsorbed oxygen atoms on the GaAs(110) surface

We report scanning tunneling microscope images of isolated oxygen atoms adsorbed on the GaAs(110) surface. The images display a dramatic voltage dependence, which arises from the energy dependence of the local state density, and provides a signature of an adsorbed electronegative atoms. At low oxygen coverages, a long-range screening of the adsorbed atoms is observed in the surrounding bare surface region, with a characteristic screening length scale of <>50 Ai<>.. AE © 1987 The American Physical Society.