Microchip for the Measurement of Seebeck Coefficients of Single Nanowires

Bismuth nanowires were electrochemically grown in ion track-etched polycarbonate membranes. Micromachining and microlithography were employed to realize a newly developed microchip for Seebeck coefficient measurements on individual nanowires. By anisotropic etching of a (100) Si wafer, an 800-nm-thick SiO₂/Si₃N₄ membrane was prepared in the chip center. The low thermal conductivity of the membrane is crucial to obtain the required temperature difference ΔT along the nanowire. The wire is electrically contacted to thin metal pads which are patterned by a new method of microscopic exposure of photoresist and a lift-off process. A ΔT between the two pairs of contact pads, located on the membrane, is established by a thin-film heater. Applying the known Seebeck coefficient of a reference film, the temperature difference at this gap is determined. Using ΔT and the measured Seebeck voltage U of the nanowire, its Seebeck coefficient can be calculated.