Crucial to the progression of the field of molecular electronics is the intellectual
conception, experimental fabrication and actual physical characterisation of molecular systems that function as electronic components. Future electronic devices could well incorporate such molecular systems in their manufacture, and expectations are high for the exploitation of molecular-scale properties. This thesis will report and discuss the stepwise construction of a variety of functional molecular wires embodied as self-assembled films on gold surfaces, providing evidence for their creation as well as characterisation of electrical properties.
The growth of molecular wire systems were observed and monitored using the quartz crystal microbalance (QCM), with further physical and chemical characterisation being obtained from x-ray photoelectron (XPS) and infrared (IR) spectroscopic studies. These investigations demonstrated that amines compete with thiols for self-assembly on gold surfaces. This may have significant consequences for stepwise growth on gold supports when amino-thiols are used as initial building blocks.
Electronic characterisation was achieved using the scanning tunnelling microscope (STM). Molecular wires self-assembled and grown on gold-coated surfaces were manipulated to exhibit rectifying behaviour, with current rectification ratios of ca. 55 at ±1 V obtained for a D-π-A type functional molecular wire. The rectifying behaviour was found to conform to the Aviram and Ratner model.
Investigations into the nature of 'current jump' events were also undertaken. These characteristic step changes in S1M tunnelling current have been employed in various studies to extract single molecule conductivities. However, the mechanism by which they occur has not been fully determined. Reported herein is evidence that suggests that 'current jumps' most likely represent events whereby STM probes make contact with surface-bound molecules, as opposed to spontaneous molecular attachment.