Fabrication of periodic surface topographies via sequential photothermal laser microsintering of silicon nanoparticle films

Photothermal laser microprocessing is exploited in order to induce sintering and compaction of thin silicon nanoparticle (Si NP) films. Ethanolic dispersions of Si NPs with an average diameter of 45 nm are spin-coated on silicon substrates yielding films with a thickness of about 400–500 nm. Scanning electron and atomic force microscopy are used for characterization of the resulting surface morphologies. Sequential processing of the coated layer with a microfocused cw-laser beam at a wavelength of 532 nm generates periodic surface structures. The periodicity of these structures is determined by the distance between adjacent laser-written lines. Despite a 1/e laser spot size of 1.4 μm, fabrication of topographic surface structures with submicrometer periodicities is feasible. In particular, surface topographies with periodicities of 600 nm and a topographic amplitude of 80 nm are fabricated. These results point to a high nonlinearity, which is attributed to the strongly activated, temperature-dependent laser sintering process. These experimental observations are reproduced qualitatively considering a simple photothermal model and an activated sintering process. Prospects of photothermal laser microsintering of nanoparticle films to fabricate biomimetic surface structures are discussed.