High-bias conductance of atom-sized Al contacts

Abstract

We measured the high-bias conductance of atom-sized Al contacts at room temperature for biases from 0.1 to 0.8 V, and studied the formation probability and the lifetime of Al single-atom contacts (SACs) under high biases. Analyses of conductance plateaus corresponding to Al SACs revealed that the formation probability of SACs decreases with increasing the bias and leads to the suppression of the first peak in the conductance histogram. The formation probability vanishes at a critical bias ${V}_{\mathrm{bc}}\ensuremath{\sim}0.8\mathrm{V}.$ On the other hand, the average plateau length, representing the average lifetime of SACs, decreases almost linearly with increasing the bias but remains finite at ${V}_{\mathrm{bc}}.$ Similar results were also obtained for Au SACs but with a higher critical bias ${V}_{\mathrm{bc}}\ensuremath{\sim}2.4\mathrm{V}.$ We consider that the reduction of the formation probability of Al and Au SACs is due to a current-induced contact instability, which takes place before the contact is reduced to a SAC. On the other hand, the mechanism of the observed linear bias dependence of the SAC plateau length is yet unclarified.