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 enha nced nucleation (BEN) of chemical vapor deposition (CVD) diamond is still a n open question. We address this question by investigating the chemical com position and structure of the material deposited during the "nucleation" st age on various substrates by near edge X-ray absorption fine structure tech nique (NEXAFS) and Raman spectroscopy. The key step of the BEN of diamond in hot filament CVD systems is the gener ation of a stable d.c.-glow discharge between the grounded substrate and a positively biased electrode. This process results in the deposition of a ca rbon based film which contains the diamond nucleation and growth centers. D ifferent materials, such as Si(100), CVD diamond films, and Si(100) onto wh ich thin films of Ni were evaporated were used as substrates. It was found that the structure of the material deposited during the d.c.-g low discharge process is affected by the nature of the substrate, The d.c.- glow discharge process applied to the Si substrate resulted in the formatio n of a graphite-like film in the earlier stages (5 min), which after prolon ged treatment time (30 min) was predominantly composed of nanosized diamond . The CVD diamond film, used as a substrate, promoted the formation of nano sized diamond particles even after 5 min of the d.c.-glow discharge process . However, C-13 labeling experiments have shown that microcrystalline diamo nd does not grow on the preexisting CVD diamond substrate under the d.c.-gl ow discharge conditions. In the case of the Ni modified Si, the deposited f ilm was graphitic in nature both after short and prolonged d.c.-glow discha rge treatment times. (C) 1999 Elsevier Science S.A. All rights reserved.