Molecular dynamics simulations for the growth of diamond-like carbon films from low kinetic energy species

In this study, molecular dynamics simulations using the Brenner potential for hydrocarbons have been used to simulate the formation of diamond-like carbon (DLC) films grown from low-energy hydrocarbon radicals (<2 eV). With these simulations, insight is gained in the processes occurring in this type of deposition. The initial surface is a previously deposited DLC surface; impinging particles include Ar⁺ ions, with an energy of 2 eV, as well as several carbon radicals and molecules, and hydrogen atoms, with an energy of 1 eV. Two different radical flux compositions were examined: in the first condition, only C, C₂, and CH were used as growth species, as well as a large flux of H atoms. In the second condition, the same carbon radicals were considered, as well as the C₂H radical and C₂H₂, C₄H₂, and C₆H₂ molecules, but without the H atom flux. These fluxes are similar to different experimental conditions in an expanding thermal Ar/C₂H₂ plasma (expanding thermal plasma, or ETP), using different influxes of acetylene. Several properties of the resulting films will be presented, focusing mainly on the carbon coordination and the bonding network. The simulations suggest that lowering the acetylene influx results in films having a more extensive bonding network, but with more H incorporated. This leads to more polymeric films having a less diamond-like character, as is expected also from experiments. The aim of this work is twofold. The first objective is to compare the structural composition of the simulated films to the structure of the experimentally deposited films by applying similar conditions. Second, the simulations can give us valuable information about the key mechanisms in the deposition process.