Evolution of micro/nano-structural arrays on crystalline silicon carbide by femtosecond laser ablation

An experimental study is conducted to investigate the multi-length scale evolution from micro/nano-structural arrays to V-grooves by femtosecond laser-irradiations, considering the effects of laser polarization and the number of scans on the periodic features and the micro/nano-structures. It is found that the evolution from micro/nano-structural arrays to V-grooves is gradual as the laser fluence, scan speed or the number of scans is increased. Laser-induced surface instability, hatching effects, Coulomb explosions, melting, and evaporation are found to be the underlying mechanisms for the micro/nano structural formation. As the laser fluence increases, the agglomerated nanoparticles change from sparse to dense, so that the boundary between the LIPSS (laser -induced periodic surface structures) becomes less obvious. The oxygen (O) elements attached to the surface of nanoparticles increase with an increase in laser fluence. A high-spatial-frequency LIPSS (HSFL) can transform to low-spatial-frequency LIPSS (LSFL) as the laser fluence excesses the ablation threshold, while the spatial period of the HSFL and LSFL is independent of fluence. It is shown that the irradiated surface evolves from a near -damage-free zone to one with a recast layer and thermal-induced micro-cracks, defined as heat-affected zones (HAZ). Near thermal damage-free micro/nano-structural arrays with different orientations on the sidewalls of the grooves are fabricated at close to the laser ablation threshold by multi-pass scanning. A self-organizing model is developed which shows that laser polarization leads to the asymmetry of energy distribution and the structural array is arranged along the main direction of energy flow. The model analysis shows a good agreement with experimental results and provides an efficient means to understand the interaction between femtosecond laser and silicon carbide (SiC).