Molecular-dynamics simulations of steady-state growth of ion-deposited tetrahedral amorphous carbon films

Molecular-dynamics calculations were performed to simulate ion beam deposit ion of diamond-like carbon films. Using the computationally efficient analy tical potentials of Tersoff and Brenner we are able to simulate more than 1 0(3) carbon atom impacts on {111} diamond, so that steady-state film proper ties can be computed and analyzed. For the Tersoff potential, we achieve sp (3) fractions approximately half of the experimentally observed values. For the more refined hydrocarbon potentials of Brenner the fraction of tetrahe drally coordinated atoms is much too low, even if structures with densities close to diamond are obtained. We show, that the sp(3) contents calculated with Tersoff's potential are an artifact related to the overbinding of spe cific bonding configurations between three- and fourfold coordinated sites. On the other hand, we can prove, that the range for the binding orbitals r epresented by the cutoff function is too short in Brenner's parametrization . If an increased C-C interaction cutoff value is chosen, we achieve a dist inct improvement in modeling the sp(3) content of deposited ta-C films. As a result we compute sp(3) fractions which lie between 52% and 95% for the C + ion energies E = 30-80 eV and are in reasonable agreement with recent exp erimental studies. (C) 2000 American Institute of Physics. [S0021-8979(00)0 3614-8].