Effect of temperature on the stability of diamond particles and continuous thin films by Raman imaging

The stability of diamond thin films grown by hot filament CVD (HFCVD) upon thermal treatment was studied using Raman imaging. By adapting two different surface pretreatments, continuous microcrystalline diamond (MCD) thin films (grain size: 100–400 nm; cross-sectional thickness: ~300 nm) as well as thin film with isolated and coalesced diamond particles (particle size: 400–600 nm; cross-sectional thickness: ~200–300 nm) were grown. The thermal stability of isolated diamond particles and continuous MCD films annealed in air at atmospheric pressure was analyzed by Raman imaging. For Raman imaging, Raman spectra were collected over an area of 85 × 85 μm using 532 nm laser (Nd:YAG) before and after thermal treatment. It was observed that the isolated diamond particles were stable for 1 h at ~750 °C, whereas for the same annealing duration, continuous MCD films grown under the same HFCVD condition were completely oxidized at 700 °C. From these results and analysis, the reason for the higher oxidation rates in the case of MCD and nanocrystalline diamond films is discussed.