Duarte Nicolas B, Mahan Gerald D, Tadigadapa Srinivas
Department of Electrical Engineering, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Nano Lett. 2009 Feb;9(2):617-22. doi: 10.1021/nl802882h.
We present thermopower measurements on free-standing, straight and "junctioned" gold nanowires using a micromachined thermoelectric workbench. Measurements on straight 70 nm diameter gold nanowires show a thermopower similar to that of bulk gold; however for "junctioned" gold nanowires we observed a hitherto unreported peak in the thermopower near room temperature. The observed enhancement can be explained by approximating the "junctioned" nanowires as tunnel junctions in combination with Coulombic effect of the electrons crossing the junction. The electron transfer across the barrier can be expected to be stochastic in nature. Under thermal equilibrium conditions and in the absence of temperature gradient across the tunnel junction, the time averaged random fluctuation of the electrons across the tunnel junction results in a net zero voltage. However, in the presence of a temperature gradient across the junction, the time averaged fluctuation of the electrons across the junction is now offset by the tunnel junction thermoelectric effect and is measured by the lock-in amplifier. A hundredfold enhancement in the ZT of "junctioned" nanowires has been observed for the gold nanowires measured over several samples.
我们使用微机械热电工作台对独立的、直的和“结型”金纳米线进行了热电功率测量。对直径为70纳米的直金纳米线的测量显示，其热电功率与块状金相似；然而，对于“结型”金纳米线，我们在室温附近观察到了一个迄今未报道的热电功率峰值。观察到的增强效应可以通过将“结型”纳米线近似为隧道结并结合电子穿过结的库仑效应来解释。可以预期，电子穿过势垒的过程本质上是随机的。在热平衡条件下且隧道结两端不存在温度梯度时，电子穿过隧道结的时间平均随机涨落导致净电压为零。然而，当结两端存在温度梯度时，电子穿过结的时间平均涨落现在会被隧道结热电效应抵消，并由锁相放大器测量。在对多个样品测量的金纳米线中，观察到“结型”纳米线的ZT提高了一百倍。
