Study of current-induced break of metal nanocontacts and its application for fabricating nano-gapped electrodes

这项研究是在我们之前对金属纳米接触的电流诱导击穿的研究的基础上进行的。该项目的目标是加深我们对击穿现象的理解，并获得对其在制备纳米间隙电极方面的应用的一些启示。我们的主要成果如下：1.我们测量了各种金属纳米触头的击穿电导，发现击穿的临界电流密度与金属的熔化温度呈正相关。这一结果表明，电流诱导的金属纳米接触击穿可能是由于接触熔化造成的。2我们成功地在低温下测量了原子尺寸的金属接触的电导两能级涨落。从TLF频率的偏置依赖关系，我们可以估算出高偏置下的有效接触温度。在77K时，银和锌触点分别在0.5V和0.4V时开始过热，而铜和…触点则开始过热更多的黄金触点没有过热迹象，最高可达0.6V。然而，在4K时，金原子大小的接触的有效温度随偏压的增加而升高。我们证明了Todorov等人提出的理论模型。很好地解释了观察到的接触温度的偏置依赖关系。3利用超高真空断开结技术，我们可以制作和保持金和铜的单原子接触，并通过施加偏置斜坡来测量它们在室温下的击穿电压。金和铜单原子接触的击穿电压分布较宽，平均分别为1.1V和0.7V。金单原子接触较高的击穿电压表明它们在高偏压下具有较好的稳定性，这与我们之前的观察结果一致。我们还发现，我们对金-单原子接触的实验结果与高偏压接触断裂的热激活模型是一致的。4.我们在多壁碳纳米管和多壁碳纳米管的电流诱导断裂方面得到了新的实验结果。并阐明了硅-硅原子大小接触的电导。较少

This research has been planned on the basis of our previous studies of current induced breakdown of metal nanocontacts. The project goal is to deepen our understanding of that breakdown phenomenon and obtain some implications towards its application for fabricating nano-gapped electrodes. Our major achievements are listed below.1 We have measured the break conductance of various metal nanocontacts and found a positive correlation between the critical current density for the breakdown and the melting temperature of metals. This result suggests that the current-induced breakdown of metal nanocontacts is presumably due to the contact melting.2 We have succeeded in measuring the the conductance two-level fluctuations (TLFs) of atom-sized metal contacts by at low temperatures. From the bias dependence of the TLF frequency, we could estimate the effective contact temperature under high biases. At 77K, silver and zinc contacts start to overheat at 0.5V and 0.4V, respectively, while copper nd … More gold contacts show no sign of overheating up to 0.6V. However, at 4K, the effective temperature of gold atom-sized contact is found to increase with the bias. We showed that the theoretical model proposed by Todorov et at. well accounts for the observed bias dependence of the contact temperature.3 By exploiting the ultra-high-vacuum break-junction technique, we could make and hold single-atom contacts of gold and copper, and measured their break voltage at room temperature by applying them a bias ramp. The break voltage exhibits a broad distribution and takes 1.1V and 0.7V, on the average, for gold and copper single-atom contacts, respectively. Higher break voltage of gold single-atom contacts indicates their superior stability under high biases, in consistent with our previous observations. We also found that our experimental results on gold-single-atom contacts are compatible with the thermal-activation model of the high-bias contact break.4 We have yielded new experimental results on the current-induced disruption of multi-walled carbon nanotubes and. benzenedithiol molecules and clarified the conductance of silicon-silicon atom-sized contacts. Less