High growth rate diamond synthesis in a large area atmospheric pressure inductively coupled plasma

Abstract

A study of diamond synthesis in an atmospheric pressure inductively coupled argon-hydrogen-methane plasma is presented. The plasma generated has an active area of 20 cm² and a free stream temperature of approximately 5000 K. Deposition experiments lasting 1 h in duration have been performed in both stagnation flow and flat plate parallel flow geometries. The diamond film deposited in both configurations are nonuniform yet fairly reproducible. The variation in the growth rates at various regions of the substrate is attributed to the variation in the surface atomic hydrogen flux. Growth rates are as high as 50 μm/h, in regions of the substrate where the atomic hydrogen flux is expected to be large. Little or no growth is observed in regions where the atomic hydrogen is expected to recombine within the thermal boundary layer before arriving at the surface. Individual particles are analyzed by micro-Raman spectroscopy. Large (50 μm) size well-faceted particles show little evidence of non-diamond carbon content and are found to be under a state of compression, displaying shifts in the principal phonon mode as great as 3 cm⁻¹.