[摘要]：Current across two metallic electrodes with a nanogap separation (similar to 50 nm) is investigated for an ac voltage applied between them. The current shows a distinct transition from the injection current regime due to quantum tunneling at low frequencies to a regime dominated by classical displacement current at high frequencies. The transition takes place at a critical frequency that increases with the applied voltage. A theoretical model treating the electrodes as a parallel RC circuit is developed; the model explains the experimental results reasonably accurately. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3702454]
