Investigation of the SH formation mechanism in Hot Filament CVD of diamond thin film by CRDS

The SH radical formation mechanism during the Hot Filament CVD (HFCVD) of diamond thin film was studied using Cavity Ringdown Spectroscopy (CRDS) for the CH$_{4}$/ H$_{2}$ mixture upon addition of traces amounts of H$_{2}$S. The absorption spectrum of the SH radical as function of different parameters (filament material, distance between filament and probing laser area of CRD cell, CH$_{4}$ and H$_{2}$S concentrations, presence and absence of substrate) was studied. The gas temperature and the SH concentration profiles were obtained. The SH radical yield saturates for CH$_{4}$ concentrations higher than 4 {\%}. From the analysis of the experimental data we expect to understand the sources and the decay channels related to the mechanism of the SH radical formation during the HFCVD of the diamond thin film. The SH translational (Doppler analysis of the line countur), rotational (rotationally resolved spectrum fitting) and vibrational (measurement of the relative populations of SH on the $v''$ = 0 and $v''$ = 1 vibronic states) temperatures were estimated.