Initial oxidation of GaAs(110): A core-level photoemission study

The initial oxidation of GaAs(110) is studied with high-resolution photoemission. The Ga and As $3d$ core levels of atoms within two to three atomic layers from the surface show small oxygen-induced shifts at about half-monolayer oxygen coverage [corresponding to about ${10}^7$ L (1 L = ${10}^{-6\mathrm{}}$ Torr sec) oxygen exposure]. The surface As atoms with a large chemical shift of 3.0 eV are significantly produced only at much higher oxygen exposures.