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Title: Probing the effect of oxygen vacancies in strontium titanate single crystals
Author: Rahman, Shams ur
Awarding Body: University of Oxford
Current Institution: University of Oxford
Date of Award: 2014
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This thesis describes investigations into the role of non-stoichiometry in the surface and bulk properties of SrTiO3 single crystals. A family of (n×n) reconstructions, where n = 2, 3, 4, 5, 6 are produced by argon ion sputtering of the SrTiO3 (111) single crystals and subsequent annealing in UHV or in an oxygen rich environment. The sputtering process introduces defects or oxygen vacancies in the surface region of the sample, whilst the annealing gives rise to surface reconstructions. The surface preparation conditions such as sputtering time, annealing temperature and environment are optimized to obtain various reconstructions in a controlled and reproducible manner. High resolution STM images of these reconstructions are also obtained and utilized in the investigation of the surface reactivity. Fullerene molecules are deposited on the reconstructed surfaces to elucidate the surface reactivity through template assisted growth. Fullerene molecules are first deposited with substrate surfaces held at room temperature. Being the most highly reduced among the (n×n) family, the 5×5 reconstruction significantly influenced the growth of fullerenes. Both C60 and C70 adsorb as individual molecules and produce clusters with magic numbers. The 4×4 and 6×6 reconstructed surfaces encourage the formation of close-packed structures upon the deposition at room temperature. When the surface covered with fullerenes is heated to a temperature of around 200 °C, epitaxial islands are observed. The 6×6 reconstructed surface appeared to be less reactive than the 4×4. Electrical transport, cathodoluminescence (CL) and electron spin resonance (ESR) experiments are also carried out to investigate the effect of oxygen vacancies on the bulk properties of UHV annealed SrTiO3 single crystals. Thermal reduction leads to carrier doping of the material, which not only gives rise to electrical conduction but also induces room temperature luminescence. Both the electrical conductivity and CL intensity increases with annealing time. The work presented in this thesis provides insight into the defect driven properties in both the surface and bulk of SrTiO3 single crystals, which could play an important role in the development of oxide-based electronic devices.
Supervisor: Castell, Martin R. Sponsor: COMSATS Institute of Information Technology (CIIT) ; Pakistan
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Materials Sciences ; Surface analysis ; Atomic scale structure and properties ; Defect analysis ; High resolution microscopy ; Surfaces ; Scanning tunnelling microscopy ; Surface nanoscience ; Surface reconstructions ; Molecular self-assembly ; Strontium Titanate ; Electron spin resonance spectroscopy ; Cathodoluminescence spectroscopy