Properties of nanocrystalline thin films of metals and semiconductors obtained at the water-oil interface

• Main Author: Stansfield, Gemma Louise
• Other Authors: Prabhakar, John Thomas
• Published: University of Manchester 2013
• Subjects: 546
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.568643

The natural world artfully harnesses the interface between immiscible liquids to carry out vital processes such as growing bones and contracting muscles. In contrast, synthetic chemists generally regard such an interface as an intractable barrier to be circumvented by the use of phase transfer reagents. A small number of studies have explored the use of the water-oil interface to synthesize inorganic nanostructures, materials that have assumed great significance in recent times. In these studies, the use of the interface leads to remarkably simple and straightforward routes to complex solids. This thesis explores the synthetic potential of the water-oil interface. Thin films consisting of Au, Ag and Pt, as well as CdS and ZnS nanocrystals adhered to the interface and spread over very large areas (square centimetres) are obtained in a single step starting with molecular precursors. The process of transfer of the films from the interface to solid substrates is examined. Further, the properties of the films thus obtained are studied in detail using charge transport measurements. Charge transport in films of arylthiol-capped Au nanocrystals exhibits strong substituent effects, with electron-donating substituents markedly decreasing conductivity. Detailed analysis suggests that the nanocrystals interact with the ligands by resonance rather than inductive effects. In stark contrast, electron-donating substituents increase conductivity in pyridinyl-capped CdS or ZnS nanocrystal films. Highly uniform films of alloyed Ag-Au nanocrystals are obtained and it is shown that the change in the composition of alloys leads to a regular and reproducible change in transport characteristics of the film, with the initially metallic films turning non-metallic with increasing Au content. In addition to exploring the electronic characteristics, the interfacial deposits were characterized using Atomic force microscopy, UV-visible spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Scanning and Transmission Electron microscopy.