Hydrogen-free diamond-like carbon (DLC) films with many sp3 bonding sites have a highly smooth surface, but very few studies have been carried out on the surface morphology of DLC films affected by the amorphous structure. In this study, the surface morphology of the DLC films was investigated on the basis of classical molecular dynamics simulations. The DLC samples composed of ten thousand carbon atoms were generated by the Melt-Quench scheme. We prepared 4 samples of various densities in order to control the ratio of sp2 / sp3 sites in the structure. As the calculation results, the ratios of sp3 sites of each structure were in proportion to the densities. We also found that the surface topography got rougher with a decrease in the sp3 sites in the structures. Sp2-rich structure had huge graphite clusters which were the series of many graphite rings over the structure, making curved surfaces, resulting in the formation of rougher surface. We discussed that the relaxation process at sp2-rich sites in the amorphous carbon structure promoted graphitization and clustering to stabilize the entire amorphous structures, and that sp3-rich films made a smooth surface because sp3 sites prevented carbon atoms from clustering.
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