Electron transport in molecular wires with transition metal contacts

A molecular wire is an organic molecule that forms a conducting bridge between electronic contacts. Single molecules are likely to be the smallest entities to conduct electricity and thus molecular wires present many interesting challenges to fundamental science as well as enormous potential for nanoelectronic technological applications. A particular challenge stems from the realization that the properties of molecular wires are strongly influenced by the combined characteristics of the molecule and the metal contacts. While gold has been the most studied contact material to date, interest in molecular wires with transition metal contacts that ar e electronically more complex than gold is growing. This thesis presents a theoretical investigation of electron transport and associated phenomena in molecular wires with transition metal contacts. An appropriate methodology is developed on the basis of Landauer theory and ab initio and semi-empirical considerations and new, physically important systems are identified. Spin-dependent transport mechanisms and device characteristics are explored for molecular wires with ferromagnetic iron contacts, systems that have not been considered previously, either theoretically or experimentally. Electron transport between iron point contacts bridged by iron atoms is also investigated. Spin-dependent transport is also studied for molecules bridging nickel contacts and a possible explanation of some experimentally observed phenomena is proposed. A novel physical phenomenon termed strong spin current rectification and a new controllable negative differential resistance mechanism with potential applications for molecular electronic technology are introduced. The phenomena predicted in this thesis should be accessible to present day experimental techniques and this work is intended to stimulate experiments directed at observing them.