Yim, C.M.; (2012) Scanning probe and spectroscopy studies of rutile TiO2(110). Doctoral thesis , UCL (University College London).

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Abstract

In this thesis, surface science techniques were employed to study the chemistry of rutile TiO2(110). Scanning tunnelling microscopy (STM) and ultraviolet photoemission spectroscopy (UPS) have been used to determine the origin of the band-gap state in rutile TiO2(110). By employing electron bombardment to vary the Ob-vac density while monitoring the band-gap state with UPS, we demonstrate that Ob-vac make dominant contribution to the photoemission peak and that is magnitude is directly proportional to the Ob-vac density. CO adsorption on the Pd/TiO2(110) surface was investigated with synchrotron radiation spectroscopies and STM. The Pd islands, which were grown by physical vapour deposition (PVD) of Pd onto the TiO2(110) substrate at ~800 K, had a pseudo-hexagonal shape and were not encapsulated with Ti^n+ (n<4) species from the substrate. In addition, it was found that CO molecules bond vertically and form various ordered overlayers on the Pd(111) islands. O2 adsorption on the cross-linked TiO2(110)-(1x2) surface was investigated with XPS, UPS and STM. The introduction of a small amount of O2 leads to a drastic reduction in the number of the Ti3+ species at the topmost surface layers and the band-gap state intensity, as well as a noticeable rise in the surface workfunction. In STM, O2 and its related molecules were found to preferably adsorb at the centre of the (1x2) strands. Current imaging tunnelling spectroscopy (CITS) was also performed on the same surface at 78 K. It was found that the densities of the two occupied states, one at -0.7 V and and another at -1.3 V, vary between different features on the surface. Moreover, whilst having less-populated occupied states, the cross-links possess an empty state at 1.2 V which cannot be detected anywhere else. This work will be compared with theoretical calculations to elucidate the geometric structure of the cross-link TiO2(110)-(1x2) surface.

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