Ge(100)2x1 substoichiometric oxidation states promoted by a Cs overlayer

High-resolution photoemission spectra from the Cs/Ge(100)2 x 1 interface were obtained for several metal coverages from 0.1 up to 1 ML. The bonding between the Cs atoms and the Ge surface was determined from the analysis of the Cs 4d and Ge 3d core level spectra. Both covalent-like and ionic-like bonds were identified in the energy shifted components of the spectra. Exposure of the interface to O-2 allowed the catalytic mechanism of the semiconductor oxidation (dramatically enhanced by the polarized metal overlayer) to be ascertained. In fact, the onset and growth of substoichiometric oxidation states was already observed at and beyond 0.25 hit Cs coverage, and 0.1 L oxygen exposure. (C) 1998 Elsevier Science B.V. All rights reserved.