Anisotropic evolution of damaged carbons of a mechanically polished diamond surface in low-temperature annealing

X Cheng and WJ Zong, DIAMOND AND RELATED MATERIALS, 90, 7-17 (2018).

DOI: 10.1016/j.diamond.2018.09.028

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 x 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.

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