(0001) and Cr 2 O 3 (0001) surfaces based on low energy electron and surface X-ray diffraction methods. However, the PhD investigation fails to provide definitive evidence for the presence or absence of surface vanadyl (V=O) species associated with atop O atoms on the surface layer of V atoms. Specifically, the best-fit structure does not include these vanadyl species, although an alternative model with similar relaxations but including vanadyl O atoms yields a reliability-factor within the variance of that of the best-fit structure.keywords: surface relaxation; surface structure; vanadium oxide; photoelectron diffraction  present address:

Scanned-energy mode photoelectron diffraction using the O 1s and V 2p emission perpendicular to the surface has been used to investigate the orientation and internal conformation of vanadyl phthalocyanine (VOPc) adsorbed on Au(111). The results confirm earlier indications from scanning tunnelling microscopy that the V=O vanadyl bond points out of, and not into, the surface. The V=O bondlength is 1.600.04 Å, not significantly different from its value in bulk crystalline VOPc. However, the V atom in the adsorbed molecule is almost coplanar with the surrounding N atoms and is thus pulled down into the approximately planar region defined by the N and C atoms by 0.52 (+0.14/-0.10) Å, relative to its location in crystalline VOPc. This change must be attributed to the bonding interaction between the molecule and the underlying metal surface.

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The surface relaxations of the rutile TiO 2 (110)(1x1) clean surface have been determined by O 1s and Ti 2p 3/2 scanned-energy mode photoelectron diffraction. The results are in excellent agreement with recent low energy electron diffraction (LEED) and medium energy ion scattering (MEIS) results, but in conflict with the results of some earlier investigations including one by surface X-ray diffraction. In particular, the bridging O atoms at the surface are found to relax outwards, rather than inwards, relative to the underlying bulk. Combined with the recent LEED and MEIS results a consistent picture of the structure of this surface is provided. While the results of the most recent theoretical total-energy calculations are qualitatively consistent with this experimental consensus, significant quantitative differences remain.