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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 A. . AE
Stroscio et al. (Mon,) studied this question.