Simulation of the non-equilibrium processes for tetrahedral 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 spa 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 spa fraction increases with ion energy, giving similar to80-85% of spa bonding at E > 30 eV. Above 200 degreesC simulations with the Brenner potential predict a sharp transition from ta-C to graphitic carbon with dominating sp(2) 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. (C) 2002 Elsevier Science B.V. All rights reserved.