The continual miniaturisation of microelectronic devices has been arguably the most important technological advance over the last fifty years. However, there exist limits beyond which current manufacturing techniques will no longer be applicable, and 'bottomup' alternatives must be sought. Single-molecule electronics is a particularly promising approach, allowing millions of 'components', identical down to the atomic level, to be
simultaneously manufactured by chemical synthesis, but it is a new field with many open problems. The research presented in this thesis aims to address some of these challenges. A number of candidate molecular electronic devices are investigated by incorporating the molecules into a symmetric gold-molecule-gold electrode structure, from which current-voltage (I-V) spectra can be obtained. The practical realisation of these structures involves
depositing an oriented organic monolayer or multilayer on a gold substrate by self-assembly or Langmuir-Blodgett deposition, to which an upper electrode must be applied. This generally takes the form of the gold tip of a Scanning Tunnelling Microscope (STM), but other entirely novel approaches are developed in-house to apply a more extended electrode to a sample, using magnetic fields to control the position. Consistency is observed between the different techniques.
These techniques are applied to the characterisation of molecular wires and Donor-Bridge-Acceptor molecular diodes. The development of an organic diode with rectifying properties
comparable to those of semiconductor devices remains an open problem, with rectification ratios at +/-1V being typically of the order of ten to a hundred. Ionically coupled bilayer and tri-layer donor-acceptor structures are developed and shown to produce rectification ratios in the thousands. These step-by-step fabrication techniques allow the facile production of donor-σ-acceptor structures that would be synthetically extremely difficult
to achieve. The size of the measured ratio is limited by noise. present in the current at reverse bias, and the actual ratio could be even higher than the quoted values. This represents an improvement of an order of magnitude, and of two to three orders of magnitude over similar devices from three years ago.