Controlled oxygen-doped diamond-like carbon film synthesized by photoemission-assisted plasma

Abstract

Controlled oxygen doping into a diamond-like carbon (DLC) film was succeeded under a current regulation by the photoemission-assisted Townsend (PAT) discharge plasma with the aid of UV-excited photoelectrons. An oxygen-doped DLC layer was formed on a non-doped DLC underlayer in the methane/argon plasma containing a certain amount of carbon dioxide as an oxygen dopant source. Oxygen-related radicals generated in the doped layer synthesis did not etch and penetrate the underlayer. However, such controlled doping failed in the photoemission-assisted glow (PAG) discharge where high-energy oxygen-related radicals etched the underlayer. A non-doped DLC layer finally capped the doped layer to build an oxygen box-doped DLC film. The dielectric constant of the film was unchanged irrespective of the amount of oxygen incorporated in the doped layer. However, very high breakdown strength was obtained, especially, over 10MV/cm in negative electrical polarization when the doped layer contained large amount of oxygen. This result suggested that the interfaces between the doped layer and the non-doped side layers exhibited an n-type barrier. The voltage characteristics in the layer syntheses under the same current regulation suggested that the UV photons passed through the doped layer and excited photoelectrons in the non-doped underlayer. The photoelectrons went back through the doped layer and emitted from the surface to cause reactions.