Thermopower measurement of gold nanowire systems using a micromachined workbench

The increased interest in new forms of alternative energy, combined with the proliferation of new nanomaterials, has revitalized the field of thermoelectric generators. Indeed, nanowires of diameter less than 10 nm have been predicted to show thermoelectric efficiencies that would rival the best mechanical generators used today. Because of their size, specialized microfabricated workbenches are necessary to probe the thermoelectric properties of these nanowires, however current generation devices suffer from a low yield of results. This dissertation presents a workbench specifically designed to address this and other limitations in previous microfabricated thermoelectric workbenches. The design process and fabrication will be discussed in detail along with verification of the desired operation, calibration, and recommended operating procedures. Thermopower measurements on free-standing gold nanowires of 70nm diameter in straight and "junctioned" configurations are presented to demonstrate the advantages of the original workbench. Straight nanowires are shown to have a thermopower similar to that of bulk gold, however for "junctioned" gold nanowires a hitherto unreported peak in the thermopower near room temperature was observed. A hundred fold enhancement in the ZT of "junctioned" gold nanowires is estimated from measurements of several samples. In addition, a study of an alternative temperature calibration method for microfabricated devices by modeling scanning thermal microscopy tip to sample interactions is presented. The model and subsequent experiments demonstrate that inclusion of a thermally insulating layer greatly improves fidelity of thermal images on microfabricated devices.