Interaction of oxygen with alkali metals at the Ge(001) surface studied by metastable deexcitation spectroscopy

Abstract

The local electronic structures of oxygen plus alkali-metal (Cs) coadsorption layers on Ge(001) surfaces have been studied by metastable deexcitation spectroscopy (MDS). Upon admission of oxygen to a Cs-saturated Ge(001) surface, the emission intensity in MDS due to the Cs 6s state (6s̃) rapidly decreased, indicating direct transfer of s̃ electrons to oxygen. This charge transfer, however, remained incomplete even with heavier exposures of oxygen. When O/Cs/Ge surfaces were thermally annealed at about 700 K, oxygen atoms adsorbed at Cs-bonded sites were transferred to Ge-bonded sites, producing GeO compounds. The compounds were desorbed when annealed at temperatures above 800 K. The results show a fairly different behavior of oxygen at alkalated Ge(001) surfaces compared to that at alkalated Si(001) surfaces.