We report on the formation of tubular structures and 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 using radially polarized doughnut-shaped laser pulses with duration of 70 fs.
Under such conditions, well reproducible tubular structures are formed whose height is rising with increasing
fluence, culminating by closing the structure on the top with formation of a microneedle with a cavity in its
base. Upon multi-pulsed irradiation, the height of the needle structures can further increase as compared to
those produced by single pulses and top part of the structure is flattened. However, at a certain number of
pulses, melting and ablation cause collapsing the entire structure. The mechanisms responsible for creating the
tubular and needle structures are discussed based on the careful analysis of the experimental observations. The
generated silicon microtubes and needles can find applications in various fields, such as intracellular delivery
of micromolecules, micro/electromechanical systems, photovoltaic devices and silicon-based photonics.
More details at Journal web page: Applied Surface Science (IF: 7.392) or check Article page