Atomic scale simulation of structural relaxation processes in tetrahedal 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 of 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 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 T_a ~1000 K. The stress relief mechanism discussed on the basis of the molecular-dynamics simulations includes structural transformations within the sp³ -bonded constituent of ta-C networks and doesn't require oriented clustering of sp² -bonded atoms.