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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy
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Probing charge transport at the single-molecule level on silicon by using cryogenic ultra-high vacuum scanning tunneling microscopy

机译：使用低温超高真空扫描隧道显微镜探测硅上单分子水平的电荷传输

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A cryogenic variable-temperature ultra-high vacuum scanning tunneling microscope is used for measuring the electrical properties of isolated cyclopentene molecules adsorbed to the degenerately p-type Si(100)-2 x 1 surface at a temperature of 80 K. Current-voltage curves taken under these conditions show negative differential resistance at positive sample bias, in agreement with previous observations at room temperature. Because of the enhanced stability of the scanning tunneling microscope at cryogenic temperatures, repeated measurements can be routinely taken over the same molecule. Taking advantage of this improved stability, we show that current-voltage curves on isolated cyclopentene molecules are reproducible and possess negligible hysteresis for a given tip-molecule distance. On the other hand, subsequent measurements with variable tip position show that the negative differential resistance voltage increases with increasing tip-molecule distance. By using a one-dimensional capacitive equivalent circuit and a resonant tunneling model, this behavior can be quantitatively explained, thus providing insight into the electrostatic potential distribution across a semiconductor-molecule-vacuum-metal tunnel junction. This model also provides a quantitative estimate for the alignment of the highest occupied molecular orbital of cyclopentene with respect to the Fermi level of the silicon substrate, thus suggesting that this experimental approach can be used for performing chemical spectroscopy at the single-molecule level on semiconductor surfaces. Overall, these results serve as the basis for a series of design rules that can be applied to silicon-based molecular electronic devices.
机译：使用低温可变温度超高真空扫描隧道显微镜在80 K的温度下测量吸附到简并p型Si（100）-2 x 1表面的孤立的环戊烯分子的电性能。电流-电压曲线在这些条件下采集的样品在正的样品偏压下显示出负的差分电阻，这与之前在室温下的观察结果一致。由于扫描隧道显微镜在低温下具有更高的稳定性，因此可以常规地对同一分子进行重复测量。利用这种改进的稳定性，我们显示出在给定的尖端分子距离下，分离的环戊烯分子上的电流-电压曲线是可重现的，并且滞后可以忽略不计。另一方面，随后的具有可变尖端位置的测量结果表明，负差分电阻电压随尖端分子距离的增加而增加。通过使用一维电容等效电路和谐振隧穿模型，可以定量地解释此行为，从而深入了解整个半导体-分子-真空-金属隧道结的静电势分布。该模型还为环戊烯的最高占据分子轨道相对于硅基板的费米能级的对准提供了定量估计，因此表明该实验方法可用于在半导体上以单分子能级进行化学光谱分析表面。总体而言，这些结果是可应用于基于硅的分子电子器件的一系列设计规则的基础。

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