Surface breakdown characteristics of polycrystalline diamond thin films in vacuum

Design and development of high voltage devices operated in vacuum environment requires a sound understanding of surface flashover phenomena across solid insulators supporting the “high voltage” electrodes. It is widely accepted that the surface flashover phenomenon is due to the field emission of electrons at the cathode “triple junction” (electrode/insulator/vacuum interface) when the applied field exceeds some threshold value. Beside the main cause of the surface breakdown, other contributing factors may be listed as (1) surface condition of the dielectric (2) type of dielectric material, (3) material type and surface condition of electrodes and (4) the operating environment. In this work we will present experimental results of surface flashover characteristics of polycrystalline diamond and other dielectric thin films as well as bulk dielectric materials in vacuum. We have concentrated our investigations on the effects of outgassing species from the dielectric material on the surface flashover phenomena. Mass spectroscopy techniques are employed to determine the outgassing species before and after the surface flashover, and the effects of these species on the initiation of the breakdown