Influence of substrate nature on the d.c.-glow discharge induced nucleation of diamond

The nature of the nucleation centers, formed during the so called bias enhanced nucleation (BEN) of chemical vapor deposition (CVD) diamond is still an open question. We address this question by investigating the chemical composition and structure of the material deposited during the “nucleation” stage on various substrates by near edge X-ray absorption fine structure technique (NEXAFS) and Raman spectroscopy.The key step of the BEN of diamond in hot filament CVD systems is the generation of a stable d.c.-glow discharge between the grounded substrate and a positively biased electrode. This process results in the deposition of a carbon based film which contains the diamond nucleation and growth centers. Different materials, such as Si(100), CVD diamond films, and Si(100) onto which thin films of Ni were evaporated were used as substrates.It was found that the structure of the material deposited during the d.c.-glow discharge process is affected by the nature of the substrate. The d.c.-glow discharge process applied to the Si substrate resulted in the formation of a graphite-like film in the earlier stages (5 min), which after prolonged treatment time (30 min) was predominantly composed of nanosized diamond. The CVD diamond film, used as a substrate, promoted the formation of nanosized diamond particles even after 5 min of the d.c.-glow discharge process. However, C-13 labeling experiments have shown that microcrystalline diamond does not grow on the pre-existing CVD diamond substrate under the d.c.-glow discharge conditions. In the case of the Ni modified Si, the deposited film was graphitic in nature both after short and prolonged d.c.-glow discharge treatment times.