In situ Raman spectroscopy of diamond during growth in a hot filament reactor

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Abstract
We report a system capable of obtaining Raman spectra during growth of carbon films in a hot filament reactor. A gated, multichannel detection system was used to discriminate against the high levels of background radiation produced by the hot substrate and the hot filament. The ability to detect and distinguish between diamond and nondiamond carbon films during growth is shown. Diamond was grown on silicon substrates at 925 °C, with a filament temperature of 2100 °C and with CH4/H2 ratios between 0.002 and 0.008. A nondiamond carbon film was produced with CH4/H2 ratio of 0.016. In order to estimate the sensitivity of the system to detect diamond during growth, the average particle size and fractional coverage of the substrate were determined when a diamond Raman signature was first observed. Currently, the system is capable of detecting diamond particles about 0.5 μm in diameter covering about 3/4 of the surface.