Mg interaction with TiO2(1 0 0): MIES and UPS(HeI) results

The interaction of Mg with TiO2(1 0 0)-(1×3) surfaces at room temperature was studied with metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy. In the early stage of Mg exposure a characteristic initial decrease of the surface work function by about 2 eV and a concomitant rise of the yield for formation of Ti3+ 3d-cations is observed; charge transfer from Mg adsorbates to Ti cations takes place. Ionically bonded Mg species seem to play a key role as nucleation sites. In the MIES spectra Mg-induced emission is found in the band gap of titania. This emission involves Mg3s electrons that are involved in bonds formed between the ionically bonded Mg+ species and additional Mg atoms. Initially, the Mg layer shows 2D growth. From the exposure dependence of the Mg3s-induced MIES signal a critical coverage of about 0.35 ML for the transition from 2D to 3D growth is derived.