Applying Ultrashort Pulsed Direct Laser Interference Patterning for Functional Surfaces

Abstract

Surface structures in the micro-and nanometre length scale exert a major influence on performance and functionality for many specialized applications in surface engineering. However, they are often limited to certain pattern scales and materials, depending on which processing technique is used. Likewise, the morphology of the topography is in complex relation to the utilized processing methodology. in this study, the generation of hierarchical surface structures in the micro-as well as the sub-micrometre scale was achieved on ceramic, polymer and metallic materials by utilizing Ultrashort pulsed Direct Laser interference patterning (USp-DLip). the morphologies of the generated patterns where examined in relation to the unique physical interaction of each material with ultrashort pulsed laser irradiation. In this context, the pattern formation on copper, CuZn37 brass and AISI 304 stainless steel was investigated in detail by means of a combination of experiment and simulation to understand the individual thermal interactions involved in USp-DLip processing. thereby, the pattern's hierarchical topography could be tailored besides achieving higher process control in the production of patterns in the sub-µm range by USp-DLip. Highly specific surface properties in nature, like the well-known lotus and shark skin effects, are closely related to surface structures in the micrometre and nanometre length scale, often involving hierarchical patterns 1. In fact, such biomimetic surface patterns have already proven to provide unique properties in several technical systems including the manipulation of contact mechanics and optical properties like light diffraction and absorption 2-4. Patterns on the threshold between the micro-and the nanometre scale also showed to provide promising surface properties for medical products, as they can tailor the adhesion of both, cells and germs 5-7. In this context, current research projects investigate the intricacies to prevent biofilm formation by surface patterning of different solid materials on the International Space Station (ISS), which endanger its crew in terms of both, health and damage to critical components 8. The predominant impact on the unique properties of patterned surfaces is defined by the scale and morphology of the surface features also including sub-patterns, which have to be adjusted specifically for each application. For instance, in antibacterial applications, feature sizes in the sub-µm length scale showed to be most effective against bacterial adhesion 7-10. The processing methodology, dealing with such delicate surface modification, needs to ensure high machining precision as well as processing speeds and costs, which are able to compete with the classical methods of surface engineering. Besides lithographic methods, laser interference-based techniques have proven their worth in generating precise surface patterns, as they provide high processing speeds with little to no need for preparation and post-processing 11. Direct Laser Interference Patterning (DLIP) usi...

Increasing Antibacterial Efficiency of Cu Surfaces by targeted Surface Functionalization via Ultrashort Pulsed Direct Laser Interference Patterning

“…The morphology as well as the topographic parameters of surface patterns induced by USP-DLIP on metals have been previously shown to be tailorable by adjusting the fluence in respect to the individual thermal substrate interaction. [43] Here, an alteration of the occurring ablation mechanisms by increasing the applied laser fluence has to be considered as well, since it prominently affects both primary pattern and sub-structure parameters. In the case of Cu, ablation behavior changes between spallation and phase explosion, as soon as substrate heating surpasses the threshold temperature of T PE = 0.9 × T cr with a critical temperature T cr of 7696 K, [44] which is shown to affect both peak geometry as well as surface morphology.…”

“…In the case of Cu, ablation behavior changes between spallation and phase explosion, as soon as substrate heating surpasses the threshold temperature of T PE = 0.9 × T cr with a critical temperature T cr of 7696 K, [44] which is shown to affect both peak geometry as well as surface morphology. [43] To create line pattern geometries befitting the scale of single cells of the tested E. coli K12 strain, laser parameters were adjusted to a fluence of 3 J cm -2 and pattern periodicity of 3 µm, which lead to ablation in the phase explosion regime on the utilized oxygen free Cu (OF-Cu) material. [43] The resulting surface morphologies both in as-processed as well as post-treated state are illustrated in Figure 1.…”

“…[43] To create line pattern geometries befitting the scale of single cells of the tested E. coli K12 strain, laser parameters were adjusted to a fluence of 3 J cm -2 and pattern periodicity of 3 µm, which lead to ablation in the phase explosion regime on the utilized oxygen free Cu (OF-Cu) material. [43] The resulting surface morphologies both in as-processed as well as post-treated state are illustrated in Figure 1.…”

Performance and Accuracy of the Shifted Laser Surface Texturing Method

“…The DLIP is an interesting method. It has advantages of the production of surface textures on a larger area simultaneously with the possibility of the production of very small surface features down to a 0.5 µm spatial period [40,41]. It has already achieved a processing speed of 0.9 m 2 /min for the surface structuring of plastics (foaming by a one-layer process) [42].…”

Stable Superhydrophobic Aluminum Surfaces Based on Laser-Fabricated Hierarchical Textures

“…On the contrary, the direct laser interference patterning (DLIP) method is able to fabricate micrometer- and even sub-micrometer-sized textures [ 22 , 23 ] at throughputs approaching 1 m 2 /min [ 24 ]. The resulting periodic microtextures have shown a promising potential for many different applications, such as improved biocompatibility, increased efficiency in solar cells, or reduced friction and wear in mechanical components [ 25 , 26 , 27 , 28 , 29 , 30 ].…”