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ta-C deposition simulations: Film properties and time-resolved dynamics of film formation

Jäger, H.-U.; Belov, A. Y.
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 Eion=10-80 eV, and for substrate temperatures Ts 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 sp2-rich surface layers agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp3 fraction in the films increases with ion energy, resulting in a highly sp3-bonded ta-C with a high compressive stress for Eion>30 eV. This trend remains also at room temperature, however with lower sp3 content and stress.
In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as Ts exceeds a critical temperature Tc. The calculated transition temperature Tc is a bit too low (Tc~100 oC for Eion=40 eV). For the ion energies Eion ≤ 80 eV, the incidence atom is predicted to come to rest in the sp2-rich surface layer. A time-resolved analysis of the film formation shows that atom subplantation leads generally to a highly tetrahedral structure, but above Tc the kinetic energy of the atoms is sufficiently large to overcome the barrier in cohesive energy between ta-C and the more stable graphite-like films.
  • Physical Review B 68 (2003) 024201-1 - 13

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Publ.-Id: 4976