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 st ress in microscopic film/substrate systems using an atomistic simulation. C riteria for choosing model parameters necessary for successful prediction o f macroscopic stress-induced phenomena (quantitatively characterized by a r eduction in binding energy) are discussed. The model is implemented in a mo lecular-dynamics simulation of compressive thermal stress at the (100) diam ond/substrate interface. The stress-induced binding-energy reduction obtain ed in the simulation is in good agreement with our model. The effect of sam ple size and local amorphization on obtained stress values is considered an d the maximum on the stress-strain dependence is explained in terms of the ''thermal spike" behavior. Similarly to results from plasma deposition expe riments, the dominant stress-induced defect is found to be the tetrahedrall y coordinated amorphous carbon (ta-C). At higher film continuities these de fects are partially converted into (100) split interstitials; at lower stre sses transformation Of a small fraction of ta-C into the graphitic sp(2) co nfiguration 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 offse t by the counteracting influence of stress on the phonon density of states.