Fabrication of inclined non-symmetrical periodic micro-structures using Direct Laser Interference Patterning

Abstract

The direct fabrication of microstructures, having a non-symmetrical morphology with controllable inclination, presents nowadays a challenging task. Natural examples of surfaces with inclined topographies have shown to provide anisotropic functionalities, which have attracted the interest of several researchers in the last years. This work presents a microfabrication technique for producing microstructures with a determined and controllable inclination angle using two-beam Direct Laser Interference Patterning. Polyimide foils are irradiated with a 4 ns UV (266 nm) laser source producing line-like structures with a period varying from 4.6 µm to 16.5 µm. The inclinations, retrieved by tilting the sample with respect to the optical axis of the setup, are changed from 0° to 75°, introducing a well controllable and defined inclination of the structure walls. The structuring parameters (laser fluence, number of laser pulses and interference period) as well as the inclination of the microstructures are correlated with the global tilting of the sample. As a result, a determined laser fluence and number of pulses are necessary to observe a remarkable non-symmetrical morphology of the structures. In addition, the presence of structural undercuts is reported, which opens the possibility for developing new direction-dependent properties on polymeric materials. As an example, preliminary results on light diffraction are presented, showing a similar behavior as blazed diffraction gratings.

Design Rules for Laser‐Treated Icephobic Metallic Surfaces for Aeronautic Applications

“…[ 45 ] On the other hand, DLIP relies its principle on the overlap of multiple coherent laser beams to generate defined interference patterns within the laser beam profile and to produce features in the micro‐ and sub‐micrometer scale. [ 46 ] The method has been successfully applied for treating materials such as metals, polymers, or organic coatings [ 47,48 ] with process rates up to 0.9 m 2 min −1 . [ 31 ] A systematic analysis of the results allowed us to propose design rules for surface features that most effectively reduce the ice adhesion strength of impact ice on metallic surfaces.…”

Self‐Limited Ice Formation and Efficient De‐Icing on Superhydrophobic Micro‐Structured Airfoils through Direct Laser Interference Patterning

“…High inclination angles have been shown to result in distortions of the DLIP texture in depth and spatial period. [ 38,39 ] An area of 100 mm × 200 mm was treated on both sides of the airfoil.…”

“…In fact, a high curvature (e.g., close to the leading edge) generates a large projection of the laser beams (i.e., a lower laser fluence), while a low curvature (e.g., on the planar sides) ensures a projection comparable to that on the flat sheet (i.e., with a higher laser fluence). [ 38 ]…”

“…In fact, a high curvature (e.g., close to the leading edge) generates a large projection of the laser beams (i.e., a lower laser fluence), while a low curvature (e.g., on the planar sides) ensures a projection comparable to that on the flat sheet (i.e., with a higher laser fluence). [38] After the laser treatment, the airfoil was treated with a hydrophobizing agent (Mecasurf, Surfactis, Angers, France) to create a stable surface chemistry with covalently bonded fluoride groups. [40] Due to the lower surface energy, the micro-structured sample became strongly water repellent (superhydrophobic) with a water contact angle (CA) exceeding 150°, while roll-ofangles (RoA) < 15°, which are typical of a non-wetting state, as reported in previous studies.…”

Experimental investigation of processing disturbances in laser surface patterning

“…Therefore, it is considered an environmentally friendly process [14]. Moreover, laser surface functionalization can be applied on a wide range of materials, from metals [15,16] to polymers [17], and thus can be deployed in different industrial sectors, e.g. in aeronautics, automotive or medical applications.…”