Unraveling the deposition mechanism in a-C:H thin-film growth: A molecular-dynamics study for the reaction behavior of C₃ and C₃H radicals with a-C:H surfaces

In this molecular-dynamics study, we present the simulated growth of thin a-C:H films using the Brenner [(Phys. Rev. B 42, 9458 (1990)] potential. These simulations are relevant for the growth of thin films, grown using low-energy hydrocarbons. In this work, we investigate the reaction mechanisms of both the linear and the cyclic isomers of C₃ and C₃H on an a-C:H surface. We found that the cyclic species are always more reactive as compared to the linear species, due to their lower stability. The C₃ species are found to be more reactive than the C₃H species, due to steric hindrance of the H atom, shielding the C atom from the surface. The different mechanisms are discussed. The resulting film properties for different flux ratios of C₃ and C₃H have also been investigated. It is shown that films as deposited from C₃ and C₃H have a low density and show low cross-linking. A clear change in microstructure is observed as the ratio between the cyclic and the linear species changes. These simulations provide insights into the reaction behavior of the investigated species, and how this influences the resulting film properties.