Time dependence of nucleation density and crystallinity of diamond in low-pressure, ion-enhanced deposition

The nucleation density and crystallinity of diamond prepared in an electron cyclotron resonance plasma by applying a negative substrate bias have been studied as a function of bias run time. The mean ion energy onto the substrate was set at approximately 30 and 50 eV by controlling the bias voltage. For short bias times of 10-60 min, the nucleation density increased with time and the highest nucleation density (10⁷-10⁸ cm^-2) and crystallinity were obtained at 60 min of biasing. For long bias times of 60-150 min, the nucleation density decreased with time accompanied by deterioration of the crystallinity, presumably due to a reduction of the effective substrate bias voltage caused by the delamination of the deposited amorphous carbon film. The incubation period for nucleation was estimated between 10 and 30 min, which was interpreted as the time to produce the amorphous carbon hydrogenated matrix characterized by relatively ordered structures with respect to carbon sp² phase.