Influence of the pressure and power on the non-equilibrium plasma chemistry of C2, C2H, C2H2,CH3 and CH4 affecting the synthesis of nanodiamond thin films from C2H2 (1%)/H2/Ar-rich plasmas

We have used a kinetic model to investigate the influence of changing the pressure (0.1-0.8 Torr) and power (100-300 W) on the non-equilibrium plasma chemistry of RF (13.56 MHz) produced C2H2 (1%)/H-2/Ar plasmas of interest for the synthesis of nanodiamond thin films. We found that the concentrations of the species C-2 (X(1)Sigma(g)(+)), C-2 (a(3) Pi(u)) and C2H are not sensitive to variations in the power but they exhibit a significant increase when the pressure decreases at high argon content in the plasma. In addition, the concentrations Of C2H2, CH4 and CH3 exhibit a slight (case of C2H2) or negligible (case of CH3 and CH4) power-dependence although they decrease (case Of C2H2 and CH4) or remain almost constant (case of CH3) as the pressure decreases. A reasonable agreement is found when comparing the model predictions with available experimental results. These findings provide a basic understanding of the plasma chemistry of hydrocarbon/Ar-rich plasma environments and, at the same time, can be of interest to optimize the processing conditions of nanodiamond films from medium pressure RF hydrocarbon/Ar-rich plasmas.