Fabrication, assembly, and electrical characterisation of gold nanowire
The work presented in this thesis has concerned the synthesis, manipulation and characterisation of gold nanowires. Porous alumina membranes have been electrochemically fabricated as templates for the deposition of gold nanowires. They consist of a thick oxide membrane, shown to be perforated by a high density array of isolated cylindrical pores, with a narrow size distribution. In addition, nanowires have been fabricated in commercially available porous alumina, and polycarbonate track-etched filtration membranes. Gold has been deposited by electrochemical and electroless techniques from a variety of solutions. A range of non-covalent interactions have been used to direct the aggregation of nanowires in solution, or assembly of nanowires on surfaces. These include hydrophobic interactions, surface wettability, hydrogen bonding, carboxylate salt formation, electrostatic interactions between charged surfactants, and biotin binding. Of particular interest is the ability to control both the placement and orientation of nanowires onto surfaces. These conditions have been best satisfied by the deposition of nanowires from solution onto surfaces patterned with alternating hydrophilic and hydrophobic stripes. Nanowires are located on the hydrophilic regions of the surface, aligned parallel to the patterned surface. The use of alternating electric fields to manipulate particles in solution is labelled dielectrophoresis. Considerable control over the assembly of nanowires is afforded by adjusting the assembly parameters. These conditions have been modelled, and investigated experimentally, to determine the optimum assembly conditions consistent with positioning a single nanowire across the electrode gap. After assembly, single nanowires displayed an Ohmic response with 35 Ω resistance values predominantly due to contact resistance between the electrode and nanowire. By optimising the assembly and cleaning procedures the contribution of contact resistance to measured resistance has been reduced below values reported elsewhere in the literature.