SPATIALLY-RESOLVED ATOMIC-HYDROGEN CONCENTRATIONS AND MOLECULAR-HYDROGEN TEMPERATURE PROFILES IN THE CHEMICAL-VAPOR-DEPOSITION OF DIAMOND

We report here a direct measurement of the spatially resolved atomic h ydrogen concentration profiles during hot-filament-assisted chemical-v apor deposition (HFCVD) of diamond films, The ground-state hydrogen (1 s(2)S(1/2) atoms generated in this process are monitored by an optical four-wave-mixing technique, third-harmonic generation (THG). For THG, a 364.6 nm dye laser beam is focused into the HFCVD reactor and the t hird-harmonic radiation near resonant with the Lyman-alpha(2p(2)P(j)(0 )<->1s(2)S(1/2)) transition in atomic hydrogen at 121.6 nm is observed , The resultant THG intensity and THG peak shift with respect to the L yman-alpha transition are both dependent on hydrogen atom concentratio n. Titration experiments based on the reaction NOCl+H-->HCl+NO were co nducted to obtain absolute hydrogen atom concentrations from the relat ive concentrations determined in the THG experiment. Spatially resolve d molecular hydrogen temperature and concentration profiles obtained b y coherent anti-Stokes Raman scattering in a similar HFCVD reactor are reported. The observed H atom concentrations exceed computed equilibr ium concentrations based on the measured gas temperatures. Transport o f the atomic hydrogen from the hot filament surfaces is discussed and diffusion is shown to be the principal mechanism controlling the H ato m distribution.