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 ͑SACs͒ 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 bc ϳ0.8 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 bc . Similar results were also obtained for Au SACs but with a higher critical bias V bc ϳ2.4 V. We consider that the reduction of the formation probability of Al and Au SACs is due to a currentinduced 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.

Simple approach to current-induced effects -- bond weakening in metal chains

“…Most notably, our simulations reproduce the sequence of critical voltages observed experimentally. These experimental findings are furthermore in accordance with earlier observations showing how Au single atom wide contacts [7,27] can withstand voltage bursts beyond 2 V, while for Al [6] this is below 0.8 V, and Pt [27] below 0.6 V. It should of course be noted that while Au, Pt, and Ir are known to form chains in experiments [28] in agreement with DFT [29], it is not clear how well this model describes the smallest contacts of the metals.…”

“…For conductors in the atomic limit the electrons essentially move through the contact without loosing energy to atomic vibrations. Therefore, single atom wide contacts and chains of a range of common metals [5][6][7][8] can sustain voltages on the order of 1 V, which corresponds to extreme current densities on the order of 10 10 A/cm 2 . The contact disruption taking place at high voltage and current is still not well understood.…”

Electromigration and the structure of metallic nanocontacts

“…Concerning the stability of the metallic nanowire's structure at high current densities, both experimental and theoretical results are known from the literature: For Pt, it has been shown that monoatomic chains form, but a large current density tends to destabilize these monoatomic wires (Nielsen et al, 2003). Similar results were found for Al and Au, but the transition was observed to occur at high voltages (0.8 V and 2.4 V) compared to Pt (0.3-0.4 V) (Mizobata et al, 2003). It has been shown by calculations that metallic wires with "magic" conductance values are stable under large current densities (Zhang et al, 2005).…”

Distribution of 1G0 Plateau Length of Au Contacts at Room Temperature

“…The appearing frequency of the 1G 0 plateaus thus represents the formation probability of the Au single-atom contacts as we discussed in our previous work. 5,6) Similarly, the 1G 0 plateau length (hereafter denoted as () indicates the ''lifetime'' of a Au singleatom contact after its formation. Since contacts of higher stability should display longer conductance plateaus, ( is also a stability measure of the Au single-atom contacts.…”