Structures and phonon properties of nanoscale fractional graphitic structures in amorphous carbon determined by molecular simulations

Abstract

Although amorphous carbon (a-C) materials are being widely used, relaxed atomic structures of a-C have not yet been investigated in detail. In this study, a-C structures were relaxed in molecular simulations, and their structural properties and phonon properties were investigated. As a result, several nanoscale fractional graphitic structures were observed in the annealed a-C structures. Further, it was found that the fractional graphitic structures caused a peak in the fractional phonon density of states of the annealed a-C structures, which corresponded to the D peak. The main phonon mode in the fractional graphitic structure with phonon frequencies of the D peak position and that of the G peak position were the distortion mode of six-membered rings, and the stretching mode of the bonds between threefold coordinated atoms, respectively. Both the distortion mode of six-membered rings and the bond-stretching mode were observed in phonon frequencies between the D peak position and the G peak position. © 2010 American Institute of Physics.