Surface vitrification of carbon by laser treatment: Insights of glass formation from molecular dynamics

Microstructural modification of carbon materials, such as carbon fibers (C_f) and pyrolytically deposited carbon, is important for engineering applications. However, the regulation of these materials is not an effortless task. To understand the impacts of thermal spikes from pulsed laser processing on the structural adaptation of amorphous carbon (a-C), we performed melt quenching by molecular dynamics (MD) simulations. Our results confirm that the vitrification behavior of carbon can be tuned by adjusting the cooling rate (R), which is controlled by the thermal spikes of laser processing. Moreover, we set up a two-step way to locate the critical cooling rate (R_c) of monoatomic carbon, which is refined by the sharp change in the environmental similarity parameter. Using this novel technique, we demonstrate that the ordering degree and the local atomic motif can be largely modified by going across a bar of 100 K/ps, which is extracted as the critical cooling rate to ensure the complete amorphization of carbon. This approach provides a criterion for both experimentally processing and theoretically simulating a-C structures. Therefore, this work provides guidelines on how to tune the amorphous carbon structures of engineering materials and provides an outlook for the wonderland of amorphous carbon materials.