Simulation of the non-equilibrium processes for tetrahedal amorphous carbon: Deposition and structural relaxation

The processes of deposition and structural relaxation of tetrahedral amorphous carbon (ta-C) films are investigated using atomistic computer simulations. Applying classical molecular dynamics with a modified hydrocarbon potential of Brenner, ion-beam deposition of carbon films was simulated for ion energies E = 10-80 eV, and for substrate temperatures ranging from 100 to 900 K. The dependence of the sp3 content and intrinsic stress in the simulated films on substrate temperature was found to agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp3 fraction increases with ion energy, giving ~80-85% of sp3 bonding at E > 30 eV. Above 200 °C simulations with the Brenner potential predict a sharp transition from ta-C to graphitic carbon with dominating sp2 bonding. Simulating thermal annealing, we show that low-temperature structural relaxation in ta-C is accompanied by a considerable stress reduction with only minor changes in the short-range order.