CC BY
11LM-O-13
Formation of hollow microneedles on silicon surface by doughnut-shaped laser pulses using single- and multi-shot irradiation
J. Hrabovskv1,2 *, M. Zukerstein1, J. Sladek1,3, I. Mirza1, Y. Levy1, and N. M. Bulgakova1
'HiLASE Centre, Institute of Physics of CAS, Dolni Brezany, Czechia 2Faculty of Mathematics and Physics, Charles University in Prague, Prague, Czechia 3Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, Prague, Czechia
Main author email adress: jan.hrabovsky@hilase.cz
Our work deals with the formation of tubular-like structures and hollow-core microneedles on the surface of monocrystalline silicon using ultrashort laser pulses. Highly deterministic surface processing is ensured by single-shot ablative modification of the sample surface as well as the multi-shot regime was used to study and modify the final structure shape. Both regimes were operated at laser fluences above the single-shot laser-induced damage threshold by a doughnut-shaped femtosecond laser pulses with duration of 35 fs (Astrella from Coherent, 800 nm wavelength). At laser fluences slightly above the ablation threshold, well reproducible tubular structures are formed whose height increases with fluence culminating with closing the structure on the top (fig. 1). Upon multi-pulsed irradiation, the height of the needle structures can be increased as compared to those produced by single pulses but, at certain number of pulses, ablation causes the entire structure to collapse. The origin of observed surface structures was discussed with respect to thermodynamics, hydrodynamics, and material stress theory.
Fig.1 Created tubular-like structures (top line, 3D and top images) and hollow-core microneedle (bottom, 3D and top images) on the surface of monocrystalline silicon created by single (left) and multiple (right) doughnut-shaped femtosecond laser pulses studied using confocal
microscopy and SEM.
Observations derived from our systematic study of hollow structures formation and their top closure offer new opportunities for applications in the fields of silicon photonics, silicon-based photovoltaic devices, and microstructures for optical field enhancement.
