Nanoporous silicon-based surface patterns fabricated by UV laser interference techniques for biological applications

The fabrication of selectively functionalized micropatterns based on nanostructured porous silicon (nanoPS) by phase mask ultraviolet laser interference is presented here. This single-step process constitutes a flexible method for the fabrication of surface patterns with tailored properties. These surface patterns consist of alternate regions of almost untransformed nanoPS and areas where nanoPS is transformed into Si nanoparticles (Si NPs) as a result of the laser irradiation process. The size of the transformed areas as well as the diameter of the Si NPs can be straightforwardly tailored by controlling the main fabrications parameters including the porosity of the nanoPS layers, the laser interference period areas, and laser fluence. The surface patterns have been found to be appropriate candidates for the development of selectively-functionalized surfaces for biological applications mainly due to the biocompatibility of the untransformed nanoPS regions.Postprint (author's final draft

Dynamics of fast pattern formation in porous silicon by laser interference

Patterns are fabricated on 290 nm thick nanostructured porous silicon layers by phase-mask laser interference using single pulses of an excimer laser (193 nm, 20 ns pulse duration). The dynamics of pattern formation is studied by measuring in real time the intensity of the diffraction orders 0 and 1 at 633 nm. The results show that a transient pattern is formed upon melting at intensity maxima sites within a time 1-µs) upon melting induced by homogeneous beam exposure and related to the different scenario for releasing the heat from hot regions. The diffraction efficiency of the pattern is finally controlled by a combination of laser fluence and initial thickness of the nanostructured porous silicon layer and the present results open perspectives on heat release management upon laser exposure as well as have potential for alternative routes for switching applications

Nanoporous silicon-based surface patterns fabricated by UV laser interference techniques for biological applications

The fabrication of selectively functionalized micropatterns based on nanostructured porous silicon (nanoPS) by phase mask ultraviolet laser interference is presented here. This single-step process constitutes a flexible method for the fabrication of surface patterns with tailored properties. These surface patterns consist of alternate regions of almost untransformed nanoPS and areas where nanoPS is transformed into Si nanoparticles (Si NPs) as a result of the laser irradiation process. The size of the transformed areas as well as the diameter of the Si NPs can be straightforwardly tailored by controlling the main fabrications parameters including the porosity of the nanoPS layers, the laser interference period areas, and laser fluence. The surface patterns have been found to be appropriate candidates for the development of selectively-functionalized surfaces for biological applications mainly due to the biocompatibility of the untransformed nanoPS regions

Ultraviolet laser patterning of porous silicon

This work reports on the fabrication of 1D fringed patterns on nanostructured porous silicon (nanoPS) layers (563, 372, and 290nm thick). The patterns are fabricated by phase-mask laser interference using single pulses of an UV excimer laser (193nm, 20ns pulse duration). The method is a single-step and flexible approach to produce a large variety of patterns formed by alternate regions of almost untransformed nanoPS and regions where its surface has melted and transformed into Si nanoparticles (NPs). The role of laser fluence (5-80mJcm-2), and pattern period (6.3-16µm) on pattern features and surface structuring are discussed. The results show that the diameter of Si NPs increases with fluence up to a saturation value of 75nm for a fluence ˜40mJcm-2. In addition, the percentage of transformed to non-transformed region normalized to the pattern period follows similar fluence dependence regardless the period and thus becomes an excellent control parameter. This dependence is fitted within a thermal model that allows for predicting the in-depth profile of the pattern. The model assumes that transformation occurs whenever the laser-induced temperature increase reaches the melting temperature of nanoPS that has been found to be 0.7 of that of crystalline silicon for a porosity of around 79%. The role of thermal gradients across the pattern is discussed in the light of the experimental results and the calculated temperature profiles, and shows that the contribution of lateral thermal flow to melting is not significant for pattern periods =6.3µm

Laser fabrication of porous silicon-based platforms for cell culturing

Postprint (published version