High-sensitivity absorption spectroscopy on a microwave plasma-assisted chemical vapour deposition diamond growth facility

High-sensitivity absorption spectroscopy using a multi-element detector was performed on a microwave plasma-assisted chemical vapour deposition (MPACVD) diamond growth facility. The absolute methyl radical column density and the line-of-sight average of the gas temperature were measured as functions of position in the discharge with input methane concentration 0-1%. The average absolute methyl radical density [CH3] was nearly independent of position in the discharge and varied in the range (1-6)x10(13) cm(-3) as the input CH4 mole fraction varied in the range 0-1%. The gas temperature was measured using H-2 emission spectroscopy and was found to be 1200 +/- 100 K independent of position throughout the discharge. An upper bound of 10(10) cm(-3) was placed on the CH density, which gives an upper bound of 0.008 on the hydrogen dissociation ratio [H]/[H-2].