The increasing bacterial resistance to antibiotics is prompting research into new approaches to design bacterial repellent surfaces. This work investigated the hot embossing of sub-micron direct laser interference patterning (DLIP) and laser-induced periodic surface structures (LIPSS) textures from stainless steel onto polypropylene samples to achieve bacterial repellent properties. Staphylococcus aureus bacteria were adhered to the textured surfaces, and adhered bacterial counts were compared to untextured polypropylene using colony-forming unit and scanning electron microscopy analysis. Both DLIP and LIPSS textures, with a periodicity of around 700 nm, significantly reduced bacterial colonization compared to untextured samples. These findings highlight the potential of DLIP and LIPSS textures as effective strategies for developing antimicrobial polymer materials.

In this study, the wetting behavior of microstructured polyethylene terephthalate (PET) foils for polar and nonpolar liquids produced by plate‐to‐plate hot embossing is investigated. For the embossing step, stainless steel plates are used as stamps, which are microstructured with single‐scaled and hierarchical textures using direct laser writing and two‐beam direct laser interference patterning. The imprinted microstructures, containing pillar‐ and line‐like textures, show increased water contact angles combined with a superoleophilic behavior. Time‐resolved measurements reveal that oil droplets spread rapidly on the hierarchical textures with velocities of up to 1.4 mm 2 s −1 . This functionalization of PET foils creates new opportunities for a wide range of industrial applications, such as the use of oil‐based instead of solvent‐based paints, an improved distribution of lubricants in mechanical components or for oil–water separation in maritime surroundings.

Increasingly compact and powerful light emitting diodes require the development of efficient optical diffusers to manage their lighting capability according to the required application. In this study, a cost‐effective strategy is demonstrated for fabricating micro‐structured polymethylmethacrylate (PMMA) diffusers for white light sources. By combining different laser‐based processes, namely direct laser engraving (DLE), direct laser writing (DLW), and direct laser interference patterning (DLIP), periodic patterns are fabricated in stainless steel surfaces with line‐ and dot‐like geometries with feature sizes ranging from 1.7 to 900 µm. The fabricated hierarchical geometries are transferred to PMMA surfaces by plate‐to‐plate hot embossing. The relationship between the surface topography and the white light scattering behavior is investigated by confocal and scanning electron microscopy combined with photospectroscopy and image processing of photographs. The triple‐scaled hierarchical structures can increase the haze up to 76% in the visible spectrum, while keeping the total transmittance over 90%, as the flat surface.

In this study, the wetting behavior of micro-structured poly(methyl methacrylate) (PMMA) surfaces produced by plate-to-plate hot embossing is investigated.The embossing tools used consist of stainless steel plates, which were previously processed by different laser methods, namely Direct Laser Engraving (DLE), Direct Laser Writing (DLW) and Direct Laser Interference Patterning (DLIP).Various textures with spatial periods in the range 1.7 to 900 μm and structure depths between 0.1 and 50 μm were produced and successfully transferred to 175 μm thick PMMA films at an embossing temperature of 130°C.In all cases, the imprints displayed the negative of the stamp textures with a difference between the stamp depth and imprint height between 6 and 16 %.The wetting behavior of the PMMA surfaces was investigated by measuring the static contact angle of distilled water as well as linseed oil.The measurements revealed an increase in the water contact angle from 79° up to 142° on the DLE-based surfaces, whereas for linseed oil, a decrease from 20° to 5° was observed for the same sample.In addition, the PMMA foils were also treated with a hydrophobizing agent in order to modify the surface chemistry.The measurements revealed no change in the water contact angle, whereas for linseed oil, contact angles up to 142° on a hierarchical surface were reached.

Recently, monitoring systems have become crucial components in industrial-scale laser machines to increase process reliability and efficiency. Particularly, monitoring methods have the potential to optimize and ensure the quality of laser surface patterning by indirectly characterizing the surface topography. Here, a diffraction measurement system, based on scatterometry, is used to determine the mean depth of laser-induced periodic surface structures (LIPSS) on stainless steel by analyzing the characteristics of the resulting diffraction patterns. To this end, LIPSS were produced with a ps-pulsed laser system operating at a wavelength of 1064 nm. The results reveal that the mean depth of LIPSS can be extracted from the intensity of the captured diffraction orders down to approximately 14 nm. This compact monitoring tool can be easily adapted to industrial-scale laser systems to improve the quality control and stability of surface microtexturing processes.

Nature provides many examples of surface structures with multiple functionalities. Some of those, such as light management and self-cleaning, are of interest for increasing the efficiency of optoelectronic devices, such as OLEDs, and for adding new surface functions. However, mimicking and transferring these textures to polymers over large areas often requires complex processes at high costs. Here, we demonstrate a low-cost strategy to fabricate hierarchically textured polyethylene terephthalate (PET) films by plate-to-plate hot embossing. Laser-machined stainless-steel plates with doublescaled hole-like textures were used as master for hot embossing. The larger structure with a period between 30 µm and 70 µm and depths up to 8 µm was produced by direct laser writing (DLW), whereas the smaller structure featuring a period of 3 µm at a depth up to 2 µm was fabricated by direct laser interference patterning (DLIP). The textured surfaces of stainless steel were then molded onto PET films at a pressure of 42 MPa and a temperature of 85°C using a hydraulic press. Topographical characterization was performed by confocal microscopy and scanning electron microscopy. Experiments have shown an increased static water contact angle up to 105°. Furthermore, the hierarchically microtextured foils were studied as out-coupling layers in OLEDs, showing a potential increase in device efficiency of up to 57%. The results thus indicate a good suitability of the developed surfaces for use in highly efficient OLEDs with easy-to-clean properties.

Structural colors can be induced on metals not only to fabricate logos or decorative motives but also to embed anti-counterfeit features for product protection. In this study, stainless steel (EN 1.4301) plates are colorized by growing a thin oxide layer using direct laser writing (DLW) and hidden anti-counterfeit measures are included on their surfaces by direct laser interference patterning (DLIP) processing. The periodic microstructures resulting from the DLIP treatment have a spatial period of 1 um and act as relief diffraction gratings, featuring a characteristic diffraction pattern. These microstructures are not visible to the human eye but are easily detectable upon shining a coherent beam on the surface. Furthermore, the reflectance over the visible spectrum of the colorized surfaces with and without the DLIP microtexture is measured, giving low differences in the color perception following the so-called "CIE L*a*b*" color space. Finally, a demonstrator is fabricated, in which colorized fields with and without the security features are shown.

Functionalized surfaces can be obtained by fabricating deterministic or stochastic structures with features in the micrometer, submicrometer and nanometer range. However, significantly enhanced surface properties can be produced by using micrometer scaled features covered by nano- or sub-micrometer structures, which occurs typically in natural examples [1] .

Nowadays, the demand for surface functionalized plastics is constantly rising. To address this demand with an industry compatible solution, here a strategy is developed for producing hierarchical microstructures on polyethylene terephthalate (PET) by hot embossing using a stainless steel stamp. The master was structured using three laser-based processing steps. First, a nanosecond-Direct Laser Writing (DLW) system was used to pattern dimples with a depth of up to 8 µm. Next, the surface was smoothed by a remelting process with a high-speed laser scanning at low laser fluence. In the third step, Direct Laser Interference Patterning (DLIP) was utilized using four interfering sub-beams to texture a hole-like substructure with a spatial period of 3.1 µm and a depth up to 2 µm. The produced stamp was used to imprint PET foils under controlled temperature and pressure. Optical confocal microscopy and scanning electron microscopy imaging showed that the hierarchical textures could be accurately transferred to the polymer. Finally, the wettability of the single- and multi-scaled textured PET surfaces was characterized with a drop shape analyzer, revealing that the highest water contact angles were reached for the hierarchical patterns. Particularly, this angle was increased from 77° on the untreated PET up to 105° for a hierarchical structure processed with a DLW spot distance of 60 µm and with 10 pulses for the DLIP treatment.

Hierarchical textures are researched experimentally and by optical simulations in the role of external outcoupling solution for OLEDs. Their full outcoupling potential, limiting factors and pathways for further increase in outcoupling are addressed.

Hierarchical textures (combining 2D periodic large and small micro textures) as an external outcoupling solution for OLEDs have been researched, both experimentally and by optical simulations. For the case of a red bottom emitting OLED, different hierarchical textures were fabricated using laser-based methods and a replication step and applied to the OLED substrate, resulting in an increased light outcoupling. Laboratory-size OLED devices with applied textured foils show a smaller increase in efficiency compared to the final large area devices. The results show that the full exploitation of textured foils in laboratory-size samples is mainly limited by the lateral size of the thin film stack area and by limited light collection area of the measuring equipment. Modeling and simulations are used to further evaluate the full prospective of hierarchical textures in large area OLED devices. Optimization of hierarchical textures is done by simultaneously changing the aspect ratios of the small and large textures and a potential of 57% improvement in EQE compared to devices without applied textures is predicted by simulations. Optimized hierarchical textures show similar outcoupling efficiencies compared to optimized single textures, while on the other hand hierarchical textures require less pronounced features, lower aspect ratios, compared to single textures to achieve the same efficiencies. Hierarchical textures also help in eliminating flat parts that limit outcoupling efficiency. Finally, the limiting factors that prevent higher outcoupling are addressed. We show that the dominant factor is non-ideal reflection from the organic thin film stack due to parasitic absorption. In addition, possible ways to further increase the outcoupling from a thick substrate are indicated.

Porous fiber structures are of great concern to many fields of life-science engineering, but require a complex assembly processes that have geometric constraints. For this reason, tremendous efforts were expended in recent years to develop micro-/nano fabrication techniques. We report on the 3D structuring of a 3.5 mm long branched hollow fiber with 150 mu m outer diameter and predefined circular pores (diameter: 30 mu m). The investigated process is based on two-photon polymerization (2PP) of the UV curing resin OrmoComp (R). The incident light of a femtosecond pulsed laser at 790 nm wavelength is used to generate the structure. Utilizing the non-linear behavior of two-photon absorption due to a tightly focused, high-intensity laser beam allows the local fabrication of three-dimensional structures in the photoresist. Voxels fabricated by 2PP are studied by controlling average laser power and exposure time. The appropriate average pulse energy and writing speed are determined to apply the optimal exposure parameters concerning the geometric accuracy and overall quality of the structure. The 2PP direct laser writing process is employed to generate the hollow fiber at an average laser power of 105 mW, and a writing speed of 5.0 mm/s. Water flowing through the fiber provides evidence that the core is hollow. (C) 2016 Elsevier B.V. All rights reserved.