Molecular-dynamics simulation of thermal stress at the (100) diamond/substrate interface: Effect of film continuity

We propose an approach to modeling the mismatch-induced residual thermal stress in microscopic film/substrate systems using an atomistic simulation. Criteria for choosing model parameters necessary for successful prediction of macroscopic stress-induced phenomena (quantitatively characterized by a reduction in binding energy) are discussed. The model is implemented in a molecular-dynamics simulation of compressive thermal stress at the (100) diamond/substrate interface. The stress-induced binding-energy reduction obtained in the simulation is in good agreement with our model. The effect of sample size and local amorphization on obtained stress values is considered and the maximum on the stress-strain dependence is explained in terms of the ''thermal spike" behavior. Similarly to results from plasma deposition experiments, the dominant stress-induced defect is found to be the tetrahedrally coordinated amorphous carbon (ta-C). At higher film continuities these defects are partially converted into (100) split interstitials; at lower stresses transformation Of a small fraction of ta-C into the graphitic sp(2) configuration takes place. The penetration depths and the distribution of the stress-induced defects are determined. The influence of residual stress on diamond thermal conductivity is studied; defects formed due to stress are shown to reduce the thermal conductivity, this effect being partially offset by the counteracting influence of stress on the phonon density of states.