Modeling the flow of activated H₂+ CH₄mixture by deposition of diamond nanostructures

Abstract

Abstract. Algorithm of the direct simulation Monte Carlo method for the flow of hydrogen and methane mixture in a cylindrical channel is developed. Heterogeneous reactions on tungsten channel surfaces are included into the model. Their effects on flows are analyzed. A onedimensional approach based on the solution of equilibrium chemical kinetics equations is used to analyze gas-phase methane decomposition. The obtained results may be useful for optimization of gas-dynamic sources of activated gas diamond synthesis.The method of Hot-Wire Chemical Vapor Deposition (HWCVD) is widely used for diamond deposition from an activated precursor gas. Its main feature is activation of a gas precursor on metallic surfaces: wires, placed in a virtually resting gas [1] or in high-speed flows [2], as well as cylindrical channels [3]. The presented work is devoted to the numerical study of gas-dynamic aspects of the rarefied gas flow in a hot tube with dissociation and recombination on the surface. The algorithm of direct simulation Monte Carlo (DSMC) method [4] with majorant frequency scheme [5] is used for the numerical analysis and optimization of approaches to deposition of diamond-like films using the hot tubes. In [6][7][8] the importance of taking into account dissociation and recombination in the analysis of flows in the tubes was shown. The use of a cylindrical channel as an activator provides better gas dissociation due to multiple collisions with the surface [6][7][8] in comparison with the case of interaction of the supersonic flow with a wire obstacle [9,10]. A one-dimensional approach based on the solution of equilibrium chemical kinetics equations was used to analyze gas-phase methane decomposition.The main goal of the presented work is to analyze the influence of the determining parameters on the composition and energy state of the gases flowing to the substrate. Particular attention is paid to the behavior of atomic hydrogen, one of the main components that determine the synthesis of diamond structures.