Abstract
Metastable de-excitation spectroscopy (MDS) has been employed for monitoring the electronic structure variation in Cs- and oxygen-adsorption processes at a Ga rich p-GaAs(001)-(4×2) surface. MDS spectra at low Cs coverages showed a peak at 2.6 eV below E F due to filling of Ga dangling bonds by charges from Cs 6s. At moderate coverages a Cs 6s-induced peak (6s̃) appeared just below E F with an abrupt increase at around θ*∼0.5, whereas contribution from substrate valence states remained on the MDS spectrum. This suggests that the Cs-induced electronic states are not fully delocalized. Upon admission of oxygen onto the surface, O 2p-induced states (2p̃) appeared with multiple peak structures, implying direct bonding of oxygen with substrate atoms even at the initial oxygenation stage. Variations in the Cs 6s̃ and O 2p̃ emissions with oxygen supply showed enhanced oxygen uptake induced by the charge transfer from the Cs 6s̃ states.
Published Version
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