Periodically ordered arrays of vertically aligned Si nanowires (Si NWs) are successfully fabricated by nanosphere lithography combined with metal-assisted chemical etching. By adjusting the etching time, both the nanowires' diameter and length can be well controlled. The conductive properties of such Si NWs and particularly their size dependence are investigated by conductive atomic force microscopy (CAFM) on individual nanowires. The results indicate that the conductance of Si NWs is greatly relevant to their diameter and length. Si NWs with smaller diameters and shorter lengths exhibit better conductive properties. Together with the I-V curve characterization, a possible mechanism is supposed with the viewpoint of size-dependent Schottky barrier height, which is further verified by the electrostatic force microscopy (EFM) measurements. This study also suggests that CAFM can act as an effective means to explore the size (or other parameters) dependence of conductive properties on individual nanostructures, which should be essential for both fabrication optimization and potential applications of nanostructures.

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A novel characterization method is introduced to measure Seebeck coefficients on individual Si nanowires (Si NWs). By using conductive atomic force microscopy with slight modifications, without any need of microfabricated devices, the Seebeck coefficients can be conveniently measured on individual Si NWs inside a large-sized vertical array in addition to the measurements on bulk substrates. The results show that the Seebeck coefficients of Si NWs are much larger than their bulk counterparts over a wide temperature range. The temperature dependence of the Seebeck coefficients of Si NWs is found to be entirely different from that of bulk Si, yet both of them agree well with the results obtained by a macroscopic method. Particularly, with this method, the Seebeck coefficients can be easily characterized on Si NWs with varied morphology, size, or doping. As an example, the Seebeck coefficients are measured on Si NWs with different lengths, and it is found that the Seebeck coefficients decrease obviously as the nanowire length increases for all measurement temperatures but the difference becomes smaller at higher temperatures. Overall, this study provides a simple but effective novel method to measure the Seebeck coefficients on individual Si NWs, which has unique advantages on exploring the size or other parameter dependence or revealing the dominant factors in thermoelectric property studies on single nanostructures.