Defect Structures of Ultrananocrystalline Diamond/Hydrogenated Amorphous Carbon Composite Films Prepared By Physical Vapor Deposition

Ultrananocrystalline diamond/hydrogenated amorphous carbon composite (UNCD/a-C:H) films were prepared by coaxial arc plasma deposition (CAPD), which is categorized as a physical vapor deposition technique, while the preparations are mainly conducted by chemical vapor deposition using a hydrocarbon carbon source gas. There have been few reports on defect structures in UNCD/a-C:H films thus far. In this study, the defect structures of UNCD/a-C:H films prepared by CAPD were investigated. Electron spin resonance measurements implied that there are a large number of dangling bonds in the films as defects. The optical absorption spectra exhibited additional optical gaps in diamond band gap due to disordered structures induced by dangling bonds and sp2- and sp3-bonded carbon atoms. The temperature dependence of the electrical conductivity indicated that the transport of carriers can be explained by a variable hopping theory, which might occur via defect states, similarly to the films prepared by conventional CVD.