Electrical discharges between platinum nanoprobe tips and gold films at nanometre gap lengths

The electrical characteristics of current-controlled electrical discharges formed in microscale and nanoscale gaps between sharpened metal cathodes and metal anodes were studied. The discharges were supplied by constant voltage source and tests were performed both with and without current control by a series regulator. The observation that all discharges (both regulated and unregulated) had limited lifetimes is notable. The total duration of regulated discharges increased as the supply voltage was increased and decreased as the current control limit was increased. In comparison, discharges produced without current regulation had larger currents and the maximum current increased as the supply voltage was increased. However, their durations were shorter than regulated discharges and were invariant with respect to supply voltage changes. Although they had lower currents, the current-controlled discharges persisted for a longer time and consequently transferred considerably more charge. Analysis of the amount of transferred charge in terms of supply voltage and discharge current limit (if the discharged was regulated) showed it corresponded to the charge stored in an ‘effective’ capacitance. Experiments suggested that the charge storage could have been associated with the current regulating device, although this was not conclusively shown. Alternatively, it was supposed that the ‘effective’ capacitance could be determined by physical instabilities inherent in small discharges, perhaps acting in combination with increased gap length due to electrode modification. Melting and ablation of the gold film anode was much less for the controlled-current discharges than for the uncontrolled ones. Additionally, the controlled-current discharges caused no observable damage to the sharpened metal cathodes.