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

Atomic-scale modeling of ta-C thin film deposition by molecular dynamics simulations is an indispensable tool for understanding growth, structure and properties of diamond-like carbon in detail. Even if much progress has been achieved in recent years, simulations comparable to experiments are for several reasons still an enormeous challenge: A large number of impacts has to be calculated in order to achieve steady-state growth conditions. Long time intervals between individual impacts, which correspond to real ion fluxes, are necessary to allow for full structural relaxation of the growing film. The simulation ensemble has to be large enough, so that the dynamics of atoms in the growing film is not affected by external thermostats. Finally, force-field calculations are necessary, which are computationally efficient, but allow for a realistic description of the chemical specifities of the growing amourphous carbon structures.

In this contribution we present classical molecular-dynamics simulations, which try to balance the above-named criteria and deliver results directly comparable to experiments. All simulations were performed on base of the Brenner-potential, but with a slightly modified interaction radius, which corrects several shortcomings of the original form. Using this computationally efficient and chemically accurate potential function we have calculated the impacts of 1200 carbon atoms with 15 ps relaxation time after every impact. In contrast to previous works our simulations were performed for realistically thermalized targets and yield steady-state film structures, which were carefully analyzed. The sp³-contents for the deposited ta-C films vary between 58 % and 90 % for the C⁺ ion energies E = 30-80 eV and are in good agreement to experimental findings.