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

The microstructure modification of carbon materials, such as carbon fibers and pyrolytically deposited carbon, is significant for engineering applications, yet their regulation is not an effortless task. To understand the impacts of thermal spikes from the pulse laser processing on the structure adaptation of amorphous carbon, we perform the melt quenching by molecular dynamics simulations. Our results confirm the vitrification behavior of carbon can be tuned by the cooling rate which is controlled by the thermal spikes of laser processing. Moreover, we set up a two-step way to locate the critical cooling rate of monoatomic carbon, which is refined by the sharp change of environment similarity parameter. Based on this novel technique, we demonstrate that the ordering degree and the local atomic motif can be largely modified if going across a bar of 100 K/ps, which is extracted as the critical cooling rate to ensure a complete amorphization of carbon. It provides a criterion for both experimentally processing and theoretically simulating of a-C structures. Therefore this work provides guidelines on how to tune the amorphous carbon structures of engineering materials and an outlook for the wonderland of amorphous carbon materials.