Evidence for subpicosecond thermal spikes in the formation of tetrahedral amorphous carbon

The molecular-dynamics technique involving the rapid cooling of a liquid to simulate an amorphous solid has been used for several years. Despite the success of the technique, the method has lacked a physical justification, and the cooling rates have been assumed to be too fast. In this paper an analysis of thermal spike cooling times in tetrahedral amorphous carbon shows that the method is reasonable and that rapid cooling rates are appropriate. Using three independent methods it is found that the thermal spike cools in less than a picosecond, considerably faster than previously recognized. An algorithm suitable for estimating cooling times in materials other than tetrahedral amorphous carbon is also presented.