Anisotropic evolution of damaged carbons of a mechanically polished diamond surface in low-temperature annealing
Abstract To clarify the anisotropic evolution of damaged carbons on a mechanically polished diamond surface under low-temperature (473 K) annealing, molecular dynamics simulation is performed in this work to represent the mechanical polishing and low-temperature annealing coupled treatment on the {100} and {110} crystal planes. Coordination number, atomic density and atomic structure analyses are employed to reveal the variation laws, and a new algorithm is further developed to extract well-arranged sp 2 carbon atoms from damaged carbon atoms. The results show that more sp 2 hybridizations appear on the {110} plane after polishing, yielding a defect density of more than 1 × 10 22  vac/cm 3 , which is the atomic origin for the graphitization in the followed low-temperature annealing. Raman spectroscopy and electron energy loss spectroscopy analyses confirm that the graphite is only detectable on the polished {110} plane. In annealing of the polished {110} plane, graphitization is a visible evolution for the damaged carbons in the topmost surface layer, and the ordered sp 2 and sp 3 hybridizations increase monotonously. Resultantly, the atomic density of damaged surface layer decreases from 3.21 g/cm 3 to 2.47 g/cm 3 , which is close to the density of graphite, 2.25 g/cm 3 . On the polished {100} plane, the ordered sp 2 and sp 3 hybridizations and atomic density of damaged surface layer change hardly upon annealing. In contrast, the amorphous sp 2 phases increase considerably. In the deeper surface layer, the amorphous sp 3 carbons grow back to the tetrahedral structures at the interface between diamond cubic and ordered sp 2 structures, which has no anisotropy in annealing.