Determination of Vibrational/Rotational Temperatures of C₂/CH/H₂, H Atom Density, and Electron Temperature by Optical Emission Spectroscopy for Microwave Plasma-Activated Diamond Growth

We investigated the vibrational/rotational temperatures, H atom density, and electron temperature by optical emission spectroscopy (OES) to understand and control the diamond growth process utilizing microwave plasma-activated chemical vapor deposition (MPCVD). The working condition of MPCVD in this study was at the pressure P = 90-150 Torr and microwave power I = 1500-3000 W for H2-CH4-Ar gas mixtures. Molecular band emissions of C2, CH, H2 were measured and analyzed to determine the rotational and vibrational temperatures of those species [2]. Actinometry utilizing line emission intensity ratios of H𝛼, H𝛽, and Ar 750 nm was applied to determine the H atom density and electron temperature [1]. Actinometry utilizes the rate balance of the excitation process by electron impacts and the de-excitation processes by spontaneous emission and neutral collisions. Neutral collisions, called quenching, are a dominant de-excitation process compared to spontaneous emission in near atmospheric pressure environments. The results will be verified by the H atom density measured by two-photon laser induced fluorescence (TALIF).

References:

[1] Gicquel, A. et al., Chemical Physics 398, 239–247 (2012).

[2] Shivkumar, G., et al., Journal of Applied Physics 119, 113301 (2016)