ta-C deposition simulations:: Film properties and time-resolved dynamics of film formation -: art. no. 024201

Ion beam deposition of carbon films was studied by molecular-dynamics simulations. Using an analytic hydrocarbon potential of Brenner with an increased C-C interaction cutoff value, deposition of films with a thickness of up to 10 nm was simulated for ion energies E-ion = 10-80 eV, and for substrate temperatures T-s ranging from 100 to 900 K. The bulk properties of the computed tetrahedral amorphous carbon (ta-C) films as well as structure and roughness of their sp(2)-rich surface layers agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp(3) fraction in the films increases with ion energy, resulting in a highly sp(3)-bonded ta-C with a high compressive stress for E-ion > 30 eV. This trend remains also at room temperature, however with lower sp(3) content and stress. In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as T-s exceeds a critical temperature T-c. The calculated value for T-c is a bit too low (T-c similar to 100degreesC for E-ion = 40 eV). For the ion energies E-ion less than or equal to 80 eV, the incidence atom is predicted to come to rest in the sp(2)-rich surface layer. A time-resolved analysis of the film formation shows that atom subplantation leads generally to a highly tetrahedral structure, but above T-C the kinetic energy of the atoms is sufficiently large to overcome the barrier in cohesive energy between ta-C and the more stable graphitelike films.