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Title: Spectroscopic studies of IrO2 and Bi2Ir2O7
Author: Kahk, Juhan Matthias
ISNI:       0000 0004 5989 7705
Awarding Body: Imperial College London
Current Institution: Imperial College London
Date of Award: 2016
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The oxides of iridium, a 5d transition metal, have recently attracted interest in a number of scientific disciplines, ranging from fundamental solid state physics, to more applied areas of research such as spintronics and catalysis. The metallic oxides IrO2 and Bi2Ir2O7, in particular, are known to be good catalysts of the commercially important oxygen evolution reaction; IrO2 has also been identified as a promising material for spin current detection, and Bi2Ir2O7 has received attention due to its unusual magnetic response at low temperatures. In the work reported in this thesis, X-ray photoelectron spectroscopy using an Al Kα photon source (XPS), synchrotron-based hard X-ray photoelectron spectroscopy (HAXPES), X-ray emission spectroscopy (XES), X-ray absorption spectroscopy (XAS), and resonant inelastic X-ray scattering (RIXS) were used to characterize the electronic structures of IrO2 and Bi2Ir2O7. The results were compared to simulated spectra derived from the results of density functional theory calculations performed by collaborators, and analyzed in terms of qualitative models of the electronic structure. Excellent agreement between theory and experiment was observed, especially if the effects of final state lifetime broadening were accounted for. A new formalism was derived that allows final state lifetime effects to be included in band structure based RIXS simulations. The results of the theoretical calculations were also used to analyze the properties of the low energy electronic states in IrO2 and Bi2Ir2O7, and it was found that in both cases there are strong deviations from the predictions of the popular jeff = 1/2 model. The results of preliminary high pressure photoemission measurements of IrO2 are also presented in this thesis, alongside a more detailed discussion of fundamental aspects of this relatively new technique. In particular, the issue of the pressure profile that is formed around the sample and the first aperture in differentially pumped spectrometers is addressed using a combination of experimental measurements and computational fluid dynamics simulations. For the flow of N2 through a 0.3 mm aperture, the calculated pressures at the plane of the sample are tabulated for a range of sample-to-cone distances and pressures of 5.0 mbar, 9.4 mbar and 30 mbar.
Supervisor: Payne, David ; Haynes, Peter Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available