Electronic Thin Film Materials

• Main Author: Hu, Jingping
• Published: University of Oxford 2007
• Subjects: 621.3815
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.491618

This thesis is concerned with investigations of the features of two types of electronic thin film materials: chemical vapour deposition (CVD) diamond and copper oxide based materials. CVD Diamond possesses excellent electrochemical properties. This thesis was concerned with investigating the fabrication and electrochemical properties of certain such diamond electrodes. The fabrication of diamond Ultramicroelectrodes (UMEs) was explored by coating tungsten needles with CVD diamond film under optimised. conditions, followed by selective insulation with different media. It was found that small grain diamond made the best electrode; large grain diamond coatings suffered from electrolyte leakage whereas nanodiamond had poor electrochemical properties. A range of tip insulation methods were examined, with most defined tips being produced by insulation with electrophoretic paint, followed by milling using Focused Ion Beam (FIB) methods. The utility of the tips prepared in this way in the SECM was demonstrated by imaging in biological media. The use of electrical conductive diamond as optically transparent electrode (OTE) opens novel applications for spectroelectrochemical studies due to the superior properties of diamond. The HFCVD diamond growth on fused silica quartz, ITO and AZO substrates was explored. The diamond membrane/ ITO structure was proposed and fabricated, exhibiting the best combination of optical transparency and electrical conductivity. Finally the changes in electrode properties as the diamond varied from macrocrystalline to nanocrystalline morphologies were studied. The second material investigated is copper oxide, specifically, cuprite (CU20) and SrCu202, a ternary Cu(I) oxide with a direct bandgap that arouses widespread interest as a p-type TCO. Their electronic structure and the nature of the hole charge carriers are topics of major current interest. The valence band and conduction band of both materials were studied by XPS in Daresbury, and XAS and XES measurements in ALS. The spectra are in good agreement with the PDOS from B3LYP calculations, showing strong hybridisation between Cu 3d and 0 2p states. Resonant Inelastic X-ray Scattering (RIXS) due to interband excitation close to Cu L3 edge threshold was first observed, conforming selection rule .6.L=O. This is the first observation of RIXS in close shell compound (dIO ). The UPS spectra of SrCu202 were measured with synchrotron radiation, and the changes in intensities of spectral features with varying photon energy were used to distinguish the contribution of 0 2p and Cu 3d states. Spectra showed that states at top of valance band are of dominant Cu 3d character and there is strong hybridisation between 0 2p and Cu 3d states which accounts for the hole mobility.