Dislocations in diamond: Dissociation into partials and their glide motion

Abstract

The dissociation of $60\ifmmode^\circ\else\textdegree\fi{}$ and screw dislocations in diamond is modeled in an approach combining isotropic elasticity theory with ab initio--based tight-binding total-energy calculations. Both dislocations are found to dissociate with a substantial lowering of their line energies. For the $60\ifmmode^\circ\else\textdegree\fi{}$ dislocation, however, an energy barrier to dissociation is found. We investigate the core structure of a screw dislocation distinguishing ``shuffle,'' ``mixed,'' and ``glide'' cores. The latter is found to be the most stable undissociated screw dislocation. Further, the glide motion of $90\ifmmode^\circ\else\textdegree\fi{}$ and $30\ifmmode^\circ\else\textdegree\fi{}$ partials is discussed in terms of a process involving the thermal formation and subsequent migration of kinks along the dislocation line. The calculated activation barriers to dislocation motion show that the $30\ifmmode^\circ\else\textdegree\fi{}$ partial is less mobile than the $90\ifmmode^\circ\else\textdegree\fi{}$ partial. Finally, high-resolution electron microscopy is performed on high-temperature, high-pressure annealed natural brown diamond, allowing the core regions of $60\ifmmode^\circ\else\textdegree\fi{}$ dislocations to be imaged. The majority of dislocations are found to be dissociated. However, in some cases, undissociated $60\ifmmode^\circ\else\textdegree\fi{}$ dislocations were also observed.