Atomic scale simulation of structural relaxation processes in tetrahedral amorphous carbon

Structural relaxation processes in tetrahedral amorphous carbon (ta-C) are examined at the atomic scale using computer simulation techniques and Brenner’s bond-order potential. The amorphous carbon networks generated by ion-beam deposition simulation are employed as structural models for as-prepared ta-C. The models possess high intrinsic compressive stresses (∼10 GPa) typical of as-grown ta-C films. Simulating annealing by the molecular-dynamics method, structural changes due to the relaxation of the ta-C networks were observed. In agreement with the experiment, it is shown that low-temperature structural relaxation in ta-C is accompanied by a considerable stress reduction with only minor changes in the structural disorder and density. A complete stress relief is found to occur at Ta∼1000 K. The stress relief mechanism discussed on the basis of the molecular-dynamics simulations includes diffusionless structural transformations within the ta-C networks and does not require oriented clustering of sp2-bonded atoms.