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

Molecular-dynamics calculations were performed to simulate ion beam deposition of diamond-like carbon films. Using the computationally efficient analytical potentials of Tersoff and Brenner we are able to simulate more than 10³ carbon atom impacts on {111} diamond, so that steady-state film properties can be computed and analyzed. For the Tersoff potential, we achieve sp³ fractions of approximately half of the experimentally observed values. For the more refined hydrocarbon potentials of Brenner the fraction of tetrahedrally coordinated atoms is much too low, even if structures with densities close to diamond are obtained. We show, that the sp³ contents calculated with Tersoff's potential are an artifact related to the overbinding of specific bonding configurations between three- and fourfold coordinated sites. On the other hand we can prove, that the range for the binding orbitals represented by the cutoff-function is too short in Brenner's parametrization. If an increased C-C interaction cutoff value is chosen, we achieve a distinct improvement in modeling the sp³ content of deposited ta-C films. As a result, we compute sp³ fractions which lie between 52 and 95% for the C⁺ ion energies E = 30-80eV and are in reasonable agreement to recent experimental studies.