Field-emission enhanced breakdown in oxygen microdischarges from direct-current to radio-frequencies

This paper reports on experimental studies of the breakdown mechanism in oxygen microdischarges generated in static and time-varying electric fields, up to radio-frequencies. Measurements were performed by using electrodes with round edges separated by a distance ranging between and , with the gas pressure from 7.5 Torr to 700 Torr. It is shown that the breakdown voltage does not obey standard scaling law for gaps of the order of a few microns for both direct current and alternating fields. A high electric field obtained in small gaps may enhance the secondary electron emission leading to the lowering of the breakdown voltage and departure from the standard scaling law. With increasing the gap size, the breakdown voltage increases since the contribution of field emission progressively reduces. Based on the breakdown voltage curves, the yields corresponding to the secondary electron production have been estimated. The threshold for field emission determined from our experimental data agree well with the value from the literature.