Deviations from the Paschen's law at short gap distances from 100 nm to 10 μm in air and nitrogen

Deviations from the Paschen's law in air and nitrogen are investigated for gaps from 100 nm to 10 μm, by using a high precision electrode positioning system. The deviation is observed when electrode gaps are smaller than 4 μm at atmospheric pressure. At distances lower than 1 μm, a nearly constant average breakdown field of 350 V/μm is evidenced in both gases with Au and Ru electrodes. A metallic plasma initiated by field emission from the cathode can explain the reduction of the breakdown voltage at such low gaps. In ambient air, the existence of a pre-breakdown current is also evidenced, probably due to the presence of water adsorbed on electrodes.