Laser-induced nanopillar structures around particles

In biomedical engineering, laser-induced periodic surface structures (LIPSSs) have been extensively applied where laser irradiation of selective laser-melted (SLMed) samples to generate LIPSS-covered free-form samples is a promising technique. Using this technique, nanopillars around a spheroidal particle that was not molten during the SLM process have been formed, indicating that nanopillars can be induced around spheroidal particles on a material surface. This study investigates the mechanism of LIPSS and nanopillar formation on SLMed and uneven surfaces experimentally and through finite-difference time-domain simulation. A 50 Hz picosecond laser with 1064 nm fixed wavelengt, 20 ps pulse duration, 0.5 J/cm2 laser fluence, and 400 mu m/s scanning speed was employed to irradiate Ti6Al4V alloy samples with 100 mu s exposure time. The results show that induced nanopillars form a concentric area around a single particle with curvature radius approximately twice the particle radius. The simulated electric field intensity is ripple-like distributed for particle size beyond 5 mu m, with approximately 1 mu m periodic length and is close to the laser wavelength. This matches the experimental results from scanning electron microscopy for 800-00 nm LIPSS periodic length, indicating that desired nanostructures can be generated by appropriately designing the surface topography before laser irradiation.