Single-step femtosecond laser-induced formation of coexisting microstructures in silicon

Various micron and submicron structures were laser-induced on silicon, including LIPSS (laser-induced periodic surface structures), grooves, conical spikes and deep craters. We used a fibre-based femtosecond (fs) laser to ablate the silicon wafer in ambient air. The formed structures strongly depend on the per-pulse laser fluence and the number of delivered pulses. We characterized the obtained structures using electron scanning microscopy and atomic force microscopy. Our results revealed interesting features such as flipping structure orientation and the coexistence of two or more types of structures that exhibit a unique wetting behaviour (contact angle with water). We found that the type of surface structures significantly influences the surface wettability.