One-step femtosecond laser-induced monocrystalline silicon structure towards enhanced nano-hardness

In this work, a one-step fs laser-induced monocrystalline silicon (Si) structure was fabricated to improve the nano-hardness properties. According to the atomic structure, three layers were found in the irradiated Si structure, namely, the amorphous Si (a-Si) layer, dislocation layer, and Si crystal layer. The a-Si layer on the surface layer was attributed to the re-solidification of melting Si material, while the dislocation layer between the a-Si and Si crystal layers contained numerous dislocations and lattice distortions, which positively affected the nano-hardness of the irradiated Si structure. The Si crystal layer was not affected by laser irradiation and maintained the initial atomic structure. This work provides a new perspective on the phase transition and microstructure study of fs laser-induced structures.