Computational details

The upper and lower layer (the height of each layers was 3.55 Å, this is 32 atoms in average) of each sample were frozen, i.e. the motion of atoms in these layers was forbidden. The initial geometry of the samples is represented in Fig. 8.14.

Figure 8.14: Initial configuration of the samples used in the third stage of the simulations; white balls represent the frozen atoms, grey balls represent the moving atoms.

To simulate a 'thermal spike' in these diamond-like amorphous carbon samples, the central layers were melted at the temperatures of 15000-27000 K. As in the previous stage of the simulation the outer frozen layers strived to limit the motion of the closest intermediate layers, hence a temperature gradient from edges to center of the sample was created. Once the liquid phase reached equilibrium (this process was controlled by monitoring the total energy of the system), the central layers were cooled to the room temperature of 300 K by a cooling rate of 10 K/fs. We found that the structure of the central amorphous carbon layers obtained after cooling depends on the temperature of heating and on the structure of the outer layers.