First-principles study of void induced stresses at a diamond (100) grain boundary

Density functional theory was used to evaluate the impact of small voids on grain boundary densification in polycrystalline diamond films. The results provide atomic scale insight into tensile stress evolution during polycrystalline film growth, where prior modeling has been largely based on continuum descriptions. Diamond is an ideal material for these studies because the atomic mobility is extremely low and thus a variety of other mechanisms that influence stress evolution can be safely ignored. For the boundary configurations that were investigated, the results indicate that significantly more densification occurs when missing atoms at grain boundaries are clustered together to form nanovoids. Increased densification also occurs with a configuration where missing atoms are in close proximity, but not directly adjacent to each other. Calculations with hydrogen trapped in the nanovoids indicate that repulsive forces can induce compressive stresses instead. (C) 2011 American Institute of Physics. [doi:10.1063/1.3544366]