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

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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