Adsorption of molecular oxygen on GaAs(001) studied using high-resolution electron energy-loss spectroscopy

High-resolution electron-energy-loss spectroscopy (EELS) has been applied to investigate the electronic structure of the GaAs(001)-c(4x4) and beta 2(2x4) reconstructions by means of successive exposure to molecular oxygen. Measurements have been performed on high-quality samples grown in situ by molecular beam epitaxy (MBE). We coupled the experimental findings with calculated spectra [density functional theory in the local density approximation (DFT-LDA)] to investigate the origin of surface states involved in the transitions and possible mechanisms of oxidation.