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The increasing importance of electrical contacts in air with micrometer spacing prompted recent experiments on the electrical breakdown behavior of these gaps. The electrical field between the contacts used in one of the experiments was analyzed using finite element analysis to model the electric field. The experimental data on the electrical breakdown voltage could be divided into three regions as a function of the gap spacing. First, at close gap spacing (/spl les/4 /spl mu/m) both the breakdown voltages as well as the electrical fields at the cathode were similar to values measured during the breakdown of vacuum gaps of less than 200 /spl mu/m. Second, at larger gaps (>6 /spl mu/m) the breakdown voltages followed Paschen's curve for the Townsend electron avalanche process in air. Finally, in between these two regions the breakdown values were below the expected values for purely vacuum breakdown or purely Townsend breakdown. The breakdown phenomena have been discussed in terms of field emission of electrons from the cathode and their effect on initiating the observed breakdown regimes.
Slade et al. (Sun,) studied this question.