Two dimensional simulation of atmospheric pressure methane-hydrogen micro- discharge for thin film depositoion T. Farouk 1 , B. Farouk 1 , A. Gutsol 2 , A. Fridman 1 1 Department of Mechanical Engineering and Mechanics, Drexel University, Philadelphia, PA, USA 2 Chevron Energy Technology Company, Richmond, CA 94802, USA Abstract: Numerical simulations were performed for an atmospheric pressure dc methane-hydrogen micro plasma using a hybrid model together with an external circuit. The model contained detailed reaction mechanisms for the gas-phase and surface reactions to predict the species densities in the discharge and the deposition characteristics and its growth rate. Special attention was given in pre- dicting the quality of the film by tracking DLC, graphitic carbon and soot deposits. Keywords: Atmospheric pressure, glow discharge, micro plasma, non-thermal, simulations. 1. Introduction Plasma assisted chemical vapor (PACVD) reactors are frequently used to deposit amorphous carbon layers on materials [1]. These layers also called dia- mond-like-carbon layers, can be deposited on a variety of substrates by PACVD using different kinds of plasmas, i.e., a microwave plasma, an electron cyclotron resonance plasma, an inductively coupled plasma or a capacitively coupled radio frequency plasma. All these plasma sources are generally maintained at low pressure for the deposition process. However, operating the plasma at low pressure as several drawbacks which include expensive vacuum sys- tems and high maintenance cost. Atmospheric pressure glow discharges are attractive for a wide range of material processing application largely due to their operation flexibility afforded by the removal of the vacuum system. Atmospheric pressure micro glow discharge of the cold type has been generated in our laboratory. Experimental studies are being performed to use the micro glow dis- charge for deposition. A hybrid model has been developed to simulate direct current methane-hydrogen plasma oper- ating at atmospheric pressure. The simulations will help to predict the composition of the plasma and to optimize the plasma parameters (power, gas flow and gas mixture) for good quality deposition. 2. Mathematical Model The model developed consists of the momentum and energy conservation for the multi-component gas mixture, and continuity equations for each component of the mix- ture (electrons, ions radicals and neutrals). The model considers a drift-diffusion approximation for the species fluxes. The species considered include 6 neutral species (CH 4 , C 2 H 6 , C 2 H 4 , C 3 H 8 , C 2 H 2 , H 2 ), 8 ionic species (CH 3 + , CH 4 + , CH 5 + , C 2 H 2 + , C 2 H 4 + , C 2 H 5 + , H 2 + , H 3 + ), 5 radicals (CH, CH 2 , CH 3 , C 2 H 5 , H) and the electron. The electric field is obtained from the simultaneous solution of the Poisson’s equation. The electron induced reaction rates, electron mobility and diffusion coefficients were obtained by solving a zero-dimensional Boltzmann equation. In the model two or more vibrational excitations for every neutral was included, since a considerable fraction of the electron energy is lost in the vibrational excitation reactions. These reactions involving the vibrationally excited species were considered only during the solution of the Boltzmann equation and not taken into account separately in order to limit the number of species in the model. 3. Schematic of the Problem Geometry Fig. 1 (a) depicts the computational domain for the simulation of atmospheric pressure micro glow discharge in methane-hydrogen for a pin to plate electrode configu- ration (metal wire tip and a planar metal surface). The inter-electrode separation is set to 400 μm. A cathode ra- dius of 500 μm was chosen so that zero-gradient boundary conditions could be applied along the boundary c-d. Fig. 1. Schematic of the a) computational domain and b) external circuit.