Properties of Nanocrystalline Thin Films of Metals and Semiconductors Obtained at the Water-Oil Interface

Abstract

The natural world artfully harnesses the interface between immiscible liquids tocarry out vital processes such as growing bones and contracting muscles. In contrast,synthetic chemists generally regard such an interface as an intractable barrier to becircumvented by the use of phase transfer reagents. A small number of studies haveexplored the use of the water-oil interface to synthesize inorganic nanostructures, materialsthat have assumed great significance in recent times. In these studies, the use ofthe interface leads to remarkably simple and straightforward routes to complex solids.This thesis explores the synthetic potential of the water-oil interface. Thin filmsconsisting of Au, Ag and Pt, as well as CdS and ZnS nanocrystals adhered to the interfaceand 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 substituenteffects, with electron-donating substituents markedly decreasing conductivity.Detailed analysis suggests that the nanocrystals interact with the ligands by resonancerather than inductive effects. In stark contrast, electron-donating substituents increaseconductivity in pyridinyl-capped CdS or ZnS nanocrystal films. Highly uniform filmsof alloyed Ag-Au nanocrystals are obtained and it is shown that the change in the compositionof alloys leads to a regular and reproducible change in transport characteristicsof the film, with the initially metallic films turning non-metallic with increasing Aucontent.In addition to exploring the electronic characteristics, the interfacial depositswere characterized using Atomic force microscopy, UV-visible spectroscopy, X-raydiffraction, X-ray photoelectron spectroscopy, Scanning and Transmission Electron microscopy.

Date of Award	1 Aug 2013
Original language	English
Awarding Institution	The University of Manchester
Supervisor	John Prabhakar (Supervisor)