3D CORE-LEVEL SHIFTS ON GE(001), CLEAN AND AFTER EXPOSURE TO NH3 AND H2O

The 3d core level shifts were analysed on clean, NH3- and OH (+H)-cove red Ge(001). Even before curve fitting, the adsorbate-induced changes prove that two surface components of equal intensity exist on the clea n surface, one shifted by 450 meV towards lower binding energy (BE) an d one overlapping with the bulk contribution. We attribute the former to the dimer up-atoms, the latter to the down-atoms. During initial ad sorption of NH3 on the down-atoms, a component at -530 meV towards hig her BE appears. The component at 450 meV is conserved, even upon compl etion of monolayer adsorption. OH (+H) quenches the 450 meV component and induces one at -560 meV and one overlapping with the bulk componen t. We attribute them to Ge-OH and Ge-H, respectively.