Optical emission characteristics of polycrystalline diamond during surface flashover in vacuum

This work presents experimental results of optical emission from polycrystalline, as well as single crystal diamonds, during the surface flashover events in a vacuum environment. Optical emission spectra were recorded and the source of this luminosity was investigated. Analysis showed that the surface flashover events were associated with relatively high intensity optical emissions. The light emission started much earlier than the voltage collapse, increased very rapidly with the breakdown, and eventually ended after few seconds; much later than the voltage across the surface was recovered. The polycrystalline diamond sample used in the experiments was produced by a microwave plasma CVD (chemical vapor deposition), and the sample surface was polished to optical quality before the experiments. The electrode material was copper, and a dc voltage was applied between the electrodes. Surface flashover voltage characteristics and breakdown voltage waveforms of both samples were determined.