Optimization of Polycrystalline CVD Diamond Seeding with the Use of sp³/sp² Raman Band Ratio

The influence of various nanodiamond colloids used for seeding nondiamond substrates in microwave plasma enhanced chemical vapour deposition diamond process was investigated. Colloids based on deionized water, isopropanol alcohol and dimethyl sulfoxide (DMSO) were used with different grain size dispersion: 150, 400 and 35 nm, respectively. The influence of growth time was also taken into consideration and bias enhanced nucleation. Microcrystalline diamond films were deposited on the seeded substrates in microwave plasma chemical vapour deposition using hydrogen-methane gas mixture. Seeding efficiency was investigated by means of scanning electron microscopy and Raman spectroscopy. Authors defined the new factor called as diamond ideality factor (di) which can give a quick estimation of quality of film and relative sp³ content. Few main peaks were identified at the following wave numbers: diamond sp³ peak 1332 $cm^{-1}$, D band peak 1355 $cm^{-1}$, C-H bending peak 1440-1480 $cm^{-1}$ and G band peak 1560 $cm^{-1}$. The best di was achieved for DMSO based colloid in all cases. The application of bias enhanced nucleation increases the diamond crystals size and the sp³/sp² ratio