Regensburg 2000 – scientific programme

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O: Oberflächenphysik

O 15: Elektronische Struktur (I)

O 15.3: Talk

Tuesday, March 28, 2000, 11:45–12:00, H37

Molecular Resonances in the Photoionization Cross Section (PIX) of Oxidic Semiconductors — •Thomas Heller¹, Oliver Böhme², and Dieter Schmeißer² — ¹Lehrstuhl Angewandte Physik - Sensorik, BTU Cottbus, E.Weinert Str.1, 03044 Cottbus, Germany — ²Instituto de Ciencia de Materiales de Madrid, ICMM-CSIC, Cantoblanco, 28049 Madrid

Despite their fascinating physical applications in sensoric there is no clear view of the electronic structure of these class of oxidic semiconductor materials. We studied the photo ionization cross sections (PIX) in a CIS like experiment of the valence states as well as the defect state and compare these to the CFS data obtained from X-ray absorption spectroscopy. While the first technique contains only transitions from a defined initial state the latter covers all the possible optical channels. We show for WO₃-films that a structural reorganization of the surface is induced by doping (Na exposure) which increases the O2p/W5d orbital mixing. Pristine TiO₂ (110) single crystals show basically the same behavior but have an initially stronger hybridization of Ti3d derived states with the O2p valence states. Upon doping the defect intensity is increased as well as the orbital hybridization. Our data give evidence that valence band derived states have almost the same orbital parentage like the defect state. They offer that the wave functions of these states are localized on a molecular scale. This is in contrast to the common treatment of resonances in the PIX which are usually discussed in terms of the resonant photoemission model, which does not include the possibility of mixed valence/defect states.