Valentin Lang

To use or not to use (direct laser interference patterning), that is the question

Direct Laser Interference Patterning (DLIP) has shown to be a fabrication technology capable of producing large area periodic surface patterns on almost any kind of material. The produced structures have been used in the past to provide surfaces with new enhanced properties. On the other hand, the industrial use of this technology is still at the beginning due to the lack of appropriate and affordable systems, especially for small and medium enterprises. In this paper, the use of DLIP for the fabrication of periodic structures using different structuring strategies and optical concepts is discussed. Different technological challenges are addressed.

World record in high speed laser surface microstructuring of polymer and steel using direct laser interference patterning

Periodic surfaces structures with micrometer or submicrometer resolution produced on the surface of components can be used to improve their mechanical, biological or optical properties. In particular, these surfaces can control the tribological performance of parts, for instance in the automotive industry. In the last years, substantial efforts have been made to develop new technologies capable to produce functionalized surfaces. One of these technologies is the Direct Laser Interference Patterning (DLIP) technology, which permits to combine high fabrication speed with high resolution even in the sub-micrometer range. In DLIP, a laser beam is split into two or more coherent beams which are guided to interfere on the work piece surface. This causes modulated laser intensities over the component’s surface, enabling the direct fabrication of a periodic pattern based on selective laser ablation or melting. Depending on the angle between the laser beams and the wavelength of the laser, the pattern’s spatial period can be perfectly controlled. In this study, we introduce new modular DLIP optical heads, developed at the Fraunhofer IWS and the Technische Universität Dresden for high-speed surface laser patterning of polymers and metals. For the first time it is shown that effective patterning speeds of up to 0.90 m2/min and 0.36 m2/min are possible on polymer and metals, respectively. Line- and dot-like surface architectures with spatial periods between 7 μm and 22 μm are shown.

Direct laser interference patterning and ultrafast laser-induced micro/nano structuring of current collectors for lithium-ion batteries

Laser-assisted modification of metals, polymers or ceramics yields a precise adjustment of wettability, biocompatibility or tribological properties for a broad range of applications. Due to a specific change of surface topography on micro- and nanometer scale, new functional properties can be achieved. A rather new scientific and technical approach is the laserassisted surface modification and structuring of metallic current collector foils for lithium-ion batteries. Prior to the thick film electrode coating processes, the formation of micro/nano-scaled surface topographies on current collectors can offer better interface adhesion, mechanical anchoring, electrical contact and reduced mechanical stress during cycling. These features in turn impact on the battery performance and the battery life-time. In order to generate the 3D surface architectures on metallic current collectors, two advanced laser processing structuring technologies: direct laser interference patterning (DLIP) and ultrafast laser-induced periodic surface structuring (LIPSS) were applied in this study. After laser structuring via DLIP and LIPSS, composite electrode materials were deposited by tape-casting on the modified current collectors. The electrode film adhesion was characterized by tensile strength measurements. The impact of various surface structures on the improvement of adhesive strength was discussed.

Optimization for high speed surface processing of metallic surfaces utilizing direct laser interference patterning

Direct Laser Interference Structuring (DLIP) is a manufacturing technology capable to functionalize large areas with high-precision periodic patterns. However, for industrial use of this emerging technology, solutions must be developed for specific requirements. With the objective of optimizing Direct Laser Interference Patterning in terms of process speed, an advanced optical module was developed that permits to superimpose two laser beams obtaining the interference pattern within an elongated area (linear spot) to meet the requirements of high-speed processing. After that, the influence of the process parameters on the quality of the surface patterns produced with the developed optical assembly was determined. It could be shown that the pulse overlap, in contrast to the applied average fluence, has a significant influence on the resulting structure heights of the produced patterns. Furthermore, it became apparent that during the course of the process, the underlying physical process dynamics seem to change, which was indicated by the resulting structure heights variations over the process. The gained findings will make a contribution to improving the quality of surface patterns produced with DLIP and to enabling reliable manufacturing qualities in the future.

Direct laser interference patterning, 20 years of development: from the basics to industrial applications

Starting from a simple concept, transferring the shape of an interference pattern directly to the surface of a material, the method of Direct Laser Interference Patterning (DLIP) has been continuously developed in the last 20 years. From lamp-pumped to high power diode-pumped lasers, DLIP permits today for the achievement of impressive processing speeds even close to 1 m2/min. The objective: to improve the performance of surfaces by the use of periodically ordered micro- and nanostructures. This study describes 20 years of evolution of the DLIP method in Germany. From the structuring of thin metallic films to bulk materials using nano- and picosecond laser systems, going through different optical setups and industrial systems which have been recently developed. Several technological applications are discussed and summarized in this article including: surface micro-metallurgy, tribology, electrical connectors, biological interfaces, thin film organic solar cells and electrodes as well as decorative elements and safety features. In all cases, DLIP has not only shown to provide outstanding surface properties but also outstanding economic advantages compared to traditional methods.

Efficient high-resolution surface patterning for 2D and 3D parts

It has been shown in the past that surfaces with controlled topographic characteristics can provide enhanced properties (e.g., low friction and wear, antibacterial behavior, or high absorption of light) compared with surfaces that have ‘random’ roughness.1 Several examples of surfaces with this kind of ordered topography can be found in nature. For instance, the surfaces of various plants and animals have evolved over thousands of years to meet survival challenges. It is therefore desirable to use this inspiration from nature to design manufacturing methods, with which controlled topography surfaces can be achieved. Laser interference lithography (LIL) can be used to produce periodic surface structures.2 During LIL, the standing wave pattern that exists at the intersection of two or more laser beams is used to expose a photosensitive layer (e.g., a resist). In the case of a negative resist, the positions that correspond to the interference maxima are photopolymerized. After subsequent resist development, a periodic variation in the surface topography can be obtained. The multistep character of LIL, however, gives rise to slow fabrication speeds and only permits the processing of planar surfaces. We have previously developed an innovative solution for high-speed surface patterning of any periodic structure in one processing step. This technique—direct laser interference patterning (DLIP)—enables the formation of periodic patterns with different features and defined long-range order.3 In DLIP, we make use of the interference between two or more laser beams. This is similar to LIL, but in the DLIP case no development of the irradiated sample is required.4, 5 Depending on the number of laser beams that are used, and their geometrical arrangement, we can produce different surface geometries (see Figure 1). For example, two-beam interference produces a 1D line-like Figure 1. Calculated intensity distribution for (a) two-beam, (b) threebeam, and (c) four-beam interference patterning. The geometrical configurations of the beams necessary to achieve the displayed geometries are also shown.

Direct laser interference patterning of metallic sleeves for roll-to-roll hot embossing

Surfaces equipped with periodic patterns with feature sizes in the micrometer, submicrometer and nanometer range present outstanding surface properties. Many of these surfaces can be found on different plants and animals. However, there are few methods capable to produce such patterns in a one-step process on relevant technological materials. Direct laser interference patterning (DLIP) provides both high resolution as well as high throughput. Recently, fabrication rates up to 1 m2·min-1 could be achieved. However, resolution was limited to a few micrometers due to typical thermal effects that arise when nanosecond pulsed laser systems are used. Therefore, this study introduces an alternative to ns-DLIP for the fabrication of multi-scaled micrometer and submicrometer structures on nickel surfaces using picosecond pulses (10 ps at a wavelength of 1064 nm). Due to the nature of the interaction process of the metallic surfaces with the ultrashort laser pulses, it was not only possible to directly transfer the shape of the interference pattern intensity distribution to the material (with spatial periods ranging from 1.5 μm to 5.7 μm), but also to selectively obtain laser induce periodic surface structures with feature sizes in the submicrometer and nanometer range. Finally, the structured nickel sleeves are utilized in a roll-to-roll hot embossing unit for structuring of polymer foils. Processing speeds up to 25 m·min-1 are reported.

Laser interference patterning and laser-induced periodic surface structure formation on metallic substrates

Laser-assisted modification of metals, polymers or ceramics yields a precise adjustment of wettability, bio-compatibility or tribological properties for a broad range of applications. Two types of advanced laser processing technologies — direct laser interference patterning and ultrafast laser-induced periodic surface structuring — were applied in this study. Formation of laser-induced periodic surface structures on metallic substrate was investigated systematically as function of wavelength, pulse duration, laser fluence and scanning speed. Line-like periodic patterns with adjustable periodicity were successfully formed on metallic substrates. For lithium-ion batteries, composite electrode materials were deposited by tape-casting on laser micro/nano-structured metallic current collectors. Tensile strength measurements revealed a tremendous improvement of film adhesion.

Large area micro-/nano-structuring using direct laser interference patterning

Smart surfaces are a source of innovation in the 21st Century. Potential applications can be found in a wide range of fields where improved optical, mechanical or biological properties can enhance the functions of products. In the last years, a method called Direct Laser Interference Patterning (DLIP) has demonstrated to be capable of fabricating a wide range of periodic surface patterns even with resolution at the nanometer and sub-micrometer scales. This article describes recent advances of the DLIP method to process 2D and 3D parts. Firstly, the possibility to fabricate periodic arrays on metallic substrates with sub-micrometer resolution is shown. After that, different concepts to process three dimensional parts are shown, including the use of Cartesian translational stages as well as an industrial robot arm. Finally, some application examples are described.