Thermoelectric phenomena can be strongly modified in nanomaterials. The determination of the absolute Seebeck coefficient is a major challenge for metrology with respect to micro- and nanostructures due to the fact that the transport properties of the bulk material are no more valid. Here, we demonstrate a method to determine the absolute Seebeck coefficient S of individual metallic nanowires. For highly pure and single crystalline silver nanowires, we show the influence of nanopatterning on S in the temperature range between 16 K and 300 K. At room temperature, a nanowire diameter below 200 nm suppresses S by 50% compared to the bulk material to less than S = 1 μVK−1, which is attributed to the reduced electron mean free path. The temperature dependence of the absolute Seebeck coefficient depends on size effects. Thermodiffusion and phonon drag are reduced with respect to the bulk material and the ratio of electron-phonon to phonon-phonon interaction is significantly increased.

We demonstrate the fabrication and improvements of our next generation Thermoelectric Nanowire Characterization Platform (TNCP) that is utilized to investigate the thermoelectric properties of individual nanowires to obtain the Seebeck coefficient S, electrical conductivity ı and thermal conductivity ț from the same test specimen. Only from these data, the so-called figure of merit ZT can be obtained for a single nanowire. In order to analyze the structural composition of single nanowires the TNCP has also to fulfill the purpose of a sample holder used in Transmission Electron Microscopy. Our second generation of TNCPs has been designed for these purposes. As before, individual nanowires are assembled on the TNCP by means of dielectrophoresis. After this assembly the nanowire is merely physically contacted to the electrodes on the TNCP. Contact generation is in first place done by an electron beam-induced deposition (EBID) process of Pt and measurements of S and ı are carried out on individual nanowires and presented here. As the EBID process is very complex and difficult to handle we have developed a novel method using a shadow mask process for the local evaporation of platinum to generate ohmic contact between the nanowire and the surrounding electrodes.

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