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 sp2 carbon atoms from damaged carbon atoms. The results show that more sp2 hybridizations appear on the {110} plane after polishing, yielding a defect density of more than 1 × 1022 vac/cm3, 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 sp2 and sp3 hybridizations increase monotonously. Resultantly, the atomic density of damaged surface layer decreases from 3.21 g/cm3 to 2.47 g/cm3, which is close to the density of graphite, 2.25 g/cm3. On the polished {100} plane, the ordered sp2 and sp3 hybridizations and atomic density of damaged surface layer change hardly upon annealing. In contrast, the amorphous sp2 phases increase considerably. In the deeper surface layer, the amorphous sp3 carbons grow back to the tetrahedral structures at the interface between diamond cubic and ordered sp2 structures, which has no anisotropy in annealing.