Role of heating and current-induced forces in the stability of atomic wires

Abstract

We investigate the role of local heating and forces on ions in the stability of current-carrying aluminum wires. For a given bias, we find that heating increases with wire length due to a redshift of the frequency spectrum. Nevertheless, the local temperature of the wire is relatively low for a wide range of biases provided good thermal contact exists between the wire and the bulk electrodes. On the contrary, current-induced forces increase substantially as a function of bias and reach bond-breaking values at about 1 V. These results suggest that local heating promotes low-bias instabilities if dissipation into the bulk electrodes is not efficient, while current-induced forces are mainly responsible for the wire breakup at large biases. We compare these results to experimental observations. Atomic wires are an ideal testbed to study transport properties at the nanoscale. 1,2 Physical phenomena that have been investigated in these systems include their quantized conductance, 3 conductance and noise oscillations as a function of the wire length, 4-7 heating, 1,8,9 and current-induced atomic motion. 8,[10][11][12] The latter two properties, in particular, are of key importance in understanding the stability of atomic wires under current flow. 12Halbritter et al. 13 and, more recently, Mizobata et al. 14,15 have explored the mechanical stability of atom-sized Al wires. These authors found that the probability of forming single-atom contacts decreases with increasing bias and that it vanishes at a critical bias of about 1 V. 16,17 In addition, several samples exhibited low-bias instabilities ͑typically at biases of 100 mV or less͒ leading to breakup of the atomic wires. Similar trends have been reported in the case of Pb ͑Ref. 13͒ and Au ͑Ref. 4͒ point contacts, suggesting that the mechanisms leading to such instabilities are material independent. These low-bias instabilities have typically been attributed to inadequate dissipation of heat into the bulk electrodes. 4,8,9 However, additional forces on ions due to current flow may also contribute, since both effects are present at any given bias.In this paper, we explore the relative role of local heating and current-induced forces in the stability of aluminum wires at different biases. We study these effects perturbatively, i.e., we first calculate current-induced forces on ions while neglecting local heating; second, we assume current-induced forces are negligible and evaluate the local temperature of the wires. This perturbative approach is supported a posteriori: we find that local heating is substantial at very low biases if poor thermal contacts exist between the wire and the bulk electrodes, 8,9,18 while current-induced forces ͑in particular, the average force per atom, see below͒ are small at low biases but increase substantially with increasing external voltage. In addition, if the heat in the wire can be dissipated efficiently into the electrodes, the local temperature in the junction will be quite low at biases for which currentinduced forces reach bond-brea...

Electrostatic modification of novel materials

“…This is due to both atomistic rearrangements and diffusion of atoms due to the steady-state current density and to inelastic electron-phonon coupling. For instance it is well known that in metal nanowires substantial local heating of the structure can occur due to electron-phonon coupling ͑van den Brom, Yanson, and Ruitenbeek, 1998;Montgomery et al, 2002;Yang et al, 2005͒. Similar effects have been studied in single-molecule junctions ͑Chen, Zwolak, and Di Ventra, 2003;Troisi, Ratner, and Nitzan, 2003͒.…”

Ab InitioAnalysis of Electron-Phonon Coupling in Molecular Devices

“…This indicates that scattering states inside the transport energy window are different from those at low bias. In particular, the pattern of P sc, RM O in the upper panel is similar to that in to local heating in the device during nonequilibrium charge transport [6,9,18,19].…”

The influence of vibronic coupling on the shape of transport characteristics in inelastic tunneling through molecules

“…Anyway, inelastic transport is quite important for the structural stability [39] and the switching possibility of the molecular electronic devices. Recently, the polaron formation on the molecule was also suggested as a possible mechanism for generating the negative differential resistance (NDR effect) and hysteresis behaviour of the V I − dependence [40].…”