Synchrotron studies of TiO2 single crystal surfaces

UoM administered thesis: Phd

  • Authors:
  • Jon Treacy

Abstract

Jon Paul William Treacy, University of ManchesterPh.D. Materials ScienceThesis title: Synchrotron studies of TiO2 single crystal surfacesDecember 2014, Word count: 34310Titanium dioxide (TiO2) is an abundant, inexpensive and non-toxic material that is most commonly used as a white pigment in paints. Since the discovery by Fujishima and Honda in 1972 that water splits into hydrogen and oxygen gas at the surface of TiO2 on exposure to sunlight, there has been a massive research effort into understanding and improving the photoactivity of TiO2. One aspect of this is the characterisation of so-called 'model' surfaces, i.e. very large single crystal faces with low levels of contamination at ultra high vacuum (UHV) pressures, allowing the study of a single structure with a minimum of unknown variables effecting experimental results.Two techniques that are used to probe surface structure, amongst many, are Surface X-ray Diffraction (SXRD) and Photoelectron Spectroscopy (PES). SXRD allows quantitative determination of surface structure with high precision, and PES reveals surface chemical composition. In the context of this thesis both of these techniques were exploited at synchrotron radiation sources, which produce light of high brightness. In addition, the development of routines for extraction of SXRD data from 2D detectors to allow SXRD analysis is described.SXRD is employed to probe the structure of anatase-TiO2(101) both in UHV and following immersion in water vapour. The optimum UHV structure is largely in agreement with that previously predicted computationally, although there are some discrepancies in terms of atomic displacements. Water immersion leads to a H2O/OH terminated surface.The surface structure of a rutile-TiO2(110)(1x1) surface, that had been prepared under non-UHV conditions, using a wet chemical preparation technique, is also determined with SXRD. The studied surface, which was highly hydrophilic, has a similar substrate termination to UHV-prepared rutile-TiO2(110)(1x1) but with adsorbed surface H2O/OH species.Finally, PES is used to gain insight into the O1s signature of surface bridging oxygens on rutile-TiO2(110), as well as those (if any) of oxygen adatoms. Concerning bridging oxygens, it is demonstrated that there is no discernable shift in the O1s core level for these atoms away from the bulk oxide peak. Regarding oxygen adatoms, no conclusive evidence of a distinct emission signal in the O1s core level or valence band spectra can be discerned, due to interference from carbon contamination.

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Original languageEnglish
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Award date1 Aug 2015