Single-Metal Nanoscale Thermocouples

We study the generation of thermoelectricity by nanoscale thermocouples (TCs) formed from a single layer of metal with cross-sectional discontinuity. Typically, a TC is formed when a second conductor is inserted between two sections of a first conductor forming two junctions situated at different temperatures. Here, we investigate the behavior of TCs formed not of two conductors but rather nanowires of the same metal of two cross-sectional areas. Monometallic TCs were constructed from a lithographically defined nanowire having one abrupt variation in width along its length, and tested at room temperature; these structures exploit a change in Seebeck coefficient that is present at these size scales. To investigate the thermoelectric properties of such “shape-engineered” TCs, nanoscale heaters were employed to set the local temperatures. Temperature profiles at the hot and cold junctions of the TCs were determined both by simulations and experiments. Results demonstrate that the magnitude of the open-circuit voltage, and hence the relative Seebeck coefficient, is a function of the parameters of the variations in the segment widths. The fabrication complexity of such shape-engineered monometallic nanowire TCs is greatly reduced compared to that of conventional bimetallic TCs, and could be mass-produced using simpler manufacturing techniques.