The electrochemical properties of nanocrystalline diamond thin-films deposited from C-60/argon and methane/nitrogen gas mixtures

Nanocrystalline diamond thin-films have been synthesized in CH4/Ar (argon) and CH4/N-2 gas mixtures without the addition of molecular hydrogen. Atomic force microscopy analysis demonstrates that the C-60/Ar films consist of h emispherical features about 150 run in diameter with a height of 20 nm. The mean roughness over a 2 x 2 mu m(2) area, based on feature height analysis , is 50 +/- 8 nm. The voltammetric response of these films in the presence of Fe(Ch)(6)(-3)/(-4), Ru(NH3)(6)(+2)/(+3), methyl viologen and 4-tert-buty lcatechol is similar to that expected for high quality microcrystalline dia mond. The results indicate that the nanocrystalline films are active withou t any conventional pretreatment, and possess semimetallic electronic proper ties over a potential range from 0.5 to -1.5 V (vs. SCE). Nanocrystalline d iamond thin-films produced from CH4/N-2 mixtures are rougher than the C-60/ Ar films, and possess electrochemical properties more closely resembling gl assy carbon. The charge carrier concentration in both types of films is bel ieved to result mainly from the sp(2) carbon in the grain boundaries.