Dresden 2003 – wissenschaftliches Programm
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DS: Dünne Schichten
DS 12: Schichtwachstum II
DS 12.1: Vortrag
Mittwoch, 26. März 2003, 15:15–15:30, GER/37
Simulation of relaxation processes in amorphous carbon films — •Alexander Belov and Hans-Ulrich Jäger — Institut für Ionenstrahlphysik und Materialforschung, Forschungszentrum Rossendorf e.V.
The atomic mechanisms of relaxation processes in carbon films during ion beam deposition and post-deposition annealing are studied using the method of molecular-dynamics with a modified hydrocarbon potential of Brenner. Deposition of films was simulated for ion energies Eion=10-80 eV and for substrate temperatures Ts=100-900 K. Using a time-resolved analysis of atomic trajectories from the film deposition simulations, a short-term temperature-dependent relaxation stage (t ∼70-1000 fs), where the film formation is influenced by Ts, was identified. During this stage, depending on Ts, the carbon atoms at metastable four- or fivefold coordinated sites can relax into either three- or fourfold positions, giving rise to graphitic or tetrahedral (ta-C) amorphous carbon films, respectively. In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as Ts exceeds a critical temperature Tc. Simulating post-deposition annealing, low-temperature structural relaxation of as-deposited ta-C was observed as evidenced by a reduction of potential energy and grown-in stress. The corresponding amorphous network rearrangements consist both in the sp3-to-sp2 conversion and in the sp2-to-sp3 one. A nearly complete stress relief in ta-C with the sp3 content of ∼80% and grown-in compressive stress of 11 GPa was simulated at an annealing temperature of ∼1000 K.