FIGURE 1. Scanning electron micrographs of the device used to quantitate the thermopower and electrical and thermal conductivity of Si nanowire arrays.

a, This false-colour image of a suspended platform shows all electrical connections. The central green area is the Si nanowire array, which is not resolved at this magnification. The four-lead yellow electrodes are used for thermometry to quantify the temperature difference across the nanowire array. The thermal gradient is established with either of the two Joule heaters (the right-hand heater is coloured red). The yellow and blue electrodes are combined to carry out four-point electrical conductivity measurements on the nanowires. The grey region underlying the nanowires and the electrodes is the 150-nm-thick SiO₂ insulator that is sandwiched between the top Si(100) single-crystal film from which the nanowires are fabricated, and the underlying Si wafer. The underlying Si wafer has been etched back to suspend the measurement platform, placing the background of this image out of focus. b, Low-resolution micrograph of the suspended platform. The electrical connections radiate outwards and support the device. c, High-resolution image of an array of 20-nm-wide Si nanowires with a Pt electrode.