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Title: Scanning tunnelling microscopy and electron spectroscopy studies of gold nanoparticles dispersed over rutile TiO2 (110)
Author: Mellor, A. G.
ISNI:       0000 0004 7225 5942
Awarding Body: UCL (University College London)
Current Institution: University College London (University of London)
Date of Award: 2017
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This thesis examines the geometric, electronic and chemical properties of Au nanoparticles supported by reduced rutile TiO2 (110), a potential heterogeneous catalyst system for many important reaction processes. Scanning tunnelling microscopy (STM) has been used to examine the nucleation properties of Au nanoparticles dispersed over a reduced rutile TiO2 (110) surface. From comparisons of the surface before and after Au deposition, and using atomic manipulation, the nucleation site of single Au atoms was directly observed to be at oxygen vacancies on the substrate (Ob-vacs). Statistical analysis of the atomic manipulation method applied provides some insight into the nature of the bonding between Au and Ob-vac sites. Synchrotron based X-ray photoelectron emission microscopy (XPEEM) was used, in conjunction with STM and low energy electron microscopy (LEEM), to probe the electronic character of Au nanoparticles as a function of particle size and coverage. Core-level binding energy measurements revealed a two stage shift in Au 4f binding energy as particle size increased. This suggests electron transfer from Ob vacs to Au occurs for small nanoparticles on the TiO2 (110) surface. To reduce experimental error, a method was developed for precisely patterning the substrate with discrete regions of varying Au coverage on the nanometre scale. The effects of beam induced photo reduction of the substrate were also investigated. High resolution electron energy loss spectroscopy was used to measure the vibrational spectrum of an Au/TiO2 sample before and after ethanol exposure. After exposure, loss features appear that correspond to acetate, however, this is not observed for Au coverages less than 0.1-0.3 MLE. From this, it is suggested that Au has a size dependent effect on the reactivity of TiO2 towards ethanol oxidation.
Supervisor: Thornton, G. ; Idriss, H. Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available