Advanced design of periodical structures by laser interference metallurgy in the micro/nano scale on macroscopic areas

Methods for micro- and nanofabrication of structures are essential for many applications in different scientific areas like physics, chemistry, and materials science. In particular, interference lithography is a widely used method to produce periodic patterns over large areas. However, this method normally requires multiple steps to obtain the final structured surface. The Laser interference Metallurgy method is similar to the interference lithography technique in that an interference pattern is used. However, when using the interference metallurgy method the only step of processing is the irradiation of the surface of the sample with an interference pattern of a high-power pulsed laser without any subsequent steps like development of a photo resist and etching. This results in a direct, periodical, and local heating of the metal based on photo-thermal nature mechanisms with a welldefined long-range order. In this work, different aspects of the "Laser Interference Metallurgy\u27; method were studied. By means of the interference theory it was demonstrated that many different periodical patterns can be explored. Moreover, the design of advanced patterns has been verified by calculating the solution of the inverse problem. This means that, for a desired periodical pattern, it is possible to establish a configuration of electromagnetic waves that reproduces the pattern. Several metallic systems were irradiated with the laser interference patterns. In the case of thin metallic film systems, the changes in the topographic types that can be obtained can be explained in terms of the laser fluence which is required to melt or vaporize one or more of the layers of the film. Moreover, it was demonstrated that the local and periodical heat of the interference pattern can successfully serve to create a phase array in a microstructural scale. Bulk metals are structured by the flow of molten material along the surface tension gradient resulting from the temperature gradient. In several cases, the results were compared to thermal simulations. Laser fluences necessary to produce different topography regimes are consistent with the thermal simulations. The consistency of the thermal simulations with the experiments was further verified by means of in-situ electrical measurements. As examples of potential applications of metallic surfaces structured by laser interference metallurgy, the modulation of optical and tribological properties is discussed.Methoden zur Mikro- und Nanostrukturierung sind unabdingbar für viele Anwendungen in unterschiedlichen Wissenschaftszweigen wie z.B. der Physik, Chemie oder in den Materialwissenschaften. Insbesondere die Interferenz-Lithographie ist eine weit verbreitete Methode, um periodische großflächige Mikrostrukturen zu erzeugen. Allerdings beinhaltet die Anwendung dieser Methode mehrere Prozeßschritte um die gewünschte Strukturierung zu realisieren. Bei der Laser Interferenz Metallurgie wird ähnlich wie bei der Interferenz Lithographie die Probe mit einem Interferenzmuster belichtet. Dieser Belichtungsschritt ist im Gegensatz zur Lithographie der einzige Bearbeitungsschritt. Weitere Schritte wie Entwicklung oder Ätzen entfallen. Bei der Laser-Interferenzmetallurgie erfolgt die Belichtung mit einem gepulsten Hochleistungslaser. Dabei werden einzelne kohärente Lichtstrahlen an der Oberfläche zur Interferenz gebracht, woraus eine direkte, ferngeordnet periodische und lokale Aufheizung des Metalls aufgrund photothermischer Wechselwirkungen erfolgt. In dieser Arbeit werden verschiedene Aspekte der Laser-Interferenzmetallurgie untersucht. Durch die Anwendung der entsprechenden Interferenz-Theorie wird gezeigt, daß verschiedenste periodische Muster bzw. Strukturen verwirklicht werden können. Eine bestimmte Form eines Interferenzmusters kann mittels Lösung des inversen Problems eingestellt werden. Daher kann für beliebige Interferenzmuster die entsprechende Konfiguration von elektromagnetischen Strahlen berechnet werden, die bei Interferenz dieses Muster reproduzieren. Mehrere metallische Systeme wurden mit Laser Interferenzmustern bestrahlt. Im Fall von metallischen Dünnfilmen können die Änderungen in der Topographie mit der Laserfluenz erklärt werden, die nötig ist, um ein oder mehrere Schichten zu schmelzen oder zu verdampfen. Desweiteren wurde demonstriert, daß der lokale und periodische Wärmeeintrag durch das Interferenzmuster erfolgreich zur Bildung neuer intermetallischer Phasen führen kann. Die Strukturierung von Bulk-Metallen erfolgt durch Materialfluss entlang des Oberflächenspannungsgradienten, der aus dem Temperaturgradienten resultiert. In verschiedenen Fällen wurden die Ergebnisse mit thermischen Simulationen verglichen. Die Laserfluenz, die nötig ist, um ein bestimmtes Topographie-Regime zu verwirklichen, ist konsistent mit den thermischen Simulationen. Die Konsistenz der thermischen Simulationen mit den Experimenten wurde weiterhin durch elektrische in-situ Messungen verifiziert. Als Beispiele für potentielle Anwendungen der mittels Laserinterfernzmetallurgie strukturierten Oberflächen wird die Modulation von optischen und tribologischen Eigenschaften diskutiert

Structuring and functionalization of non-metallic materials using direct laser interference patterning: A review

Direct laser interference patterning (DLIP) is a laser-based surface structuring method that stands out for its high throughput, flexibility and resolution for laboratory and industrial manufacturing. This top-down technique relies on the formation of an interference pattern by overlapping multiple laser beams onto the sample surface and thus producing a periodic texture by melting and/or ablating the material. Driven by the large industrial sectors, DLIP has been extensively used in the last decades to functionalize metallic surfaces, such as steel, aluminium, copper or nickel. Even so, DLIP processing of non-metallic materials has been gaining popularity in promising fields such as photonics, optoelectronics, nanotechnology and biomedicine. This review aims to comprehensively collect the main findings of DLIP structuring of polymers, ceramics, composites, semiconductors and other non-metals and outline their most relevant results. This contribution also presents the mechanisms by which laser radiation interacts with non-metallic materials in the DLIP process and summarizes the developed surface functions and their applications in different fields.Fil: Mulko, Lucinda. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemani

Optical Enhancement of Fluorine-Doped Tin Oxide Thin Films using Infrared Picosecond Direct Laser Interference Patterning

Surface texturization of Transparent Conductive Oxides (TCOs) is a well-known strategy to enhance the light-trapping capabilities of thin-film solar cells and thus, to increase their power conversion efficiency. Herein, the surface modification of fluorine-doped tin oxide (FTO) using picosecond infrared direct laser interference patterning (DLIP) is presented. The surface characterization exhibits periodic microchannels, which act as diffraction gratings yielding an increase in the average diffuse transmittance up to 870% in the spectral range of 400–1000 nm. Despite the one dimensionality of the microstructures, the films did not acquire a significant anisotropic electrical behavior, but a partial deterioration of their conductivity is observed as a result of the removal of conductive material. This work proposes the feasibility of trading off a portion of the electrical conductivity to obtain a substantial improvement in the optical performance.Fil: Heffner, Herman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto de Química del Sur. Universidad Nacional del Sur. Departamento de Química. Instituto de Química del Sur; Argentina. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Grupo Vinculado Instituto de Ingeniería Química | Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Grupo Vinculado Instituto de Ingeniería Química; Argentina. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés Fabián. Fraunhofer–Institut für Werkstoff und Strahltechnik; Alemania. Technische Universität Dresden; Alemani

Fabrication of multifunctional titanium surfaces by producing hierarchical surface patterns using laser based ablation methods

Textured implant surfaces with micrometer and sub-micrometer features can improve contact properties like cell adhesion and bacteria repellency. A critical point of these surfaces is their mechanical stability during implantation. Therefore, strategies capable to provide both biocompatibility for an improved implant healing and resistance to wear for protecting the functional surface are required. In this work, laser-based fabrication methods have been used to produce hierarchical patterns on titanium surfaces. Using Direct Laser Writing with a nanosecond pulsed laser, crater-like structures with a separation distance of 50 µm are produced on unpolished titanium surfaces. Directly on this texture, a hole-like pattern with 5 µm spatial period is generated using Direct Laser Interference Patterning with picosecond pulses. While the smaller features should reduce the bacterial adhesion, the larger geometry was designed to protect the smaller features from wear. On the multifunctional surface, the adherence of E. Coli bacteria is reduced by 30% compared to the untreated reference. In addition, wear test performed on the multiple-scale patterns demonstrated the possibility to protect the smaller features by the larger craters. Also, the influence of the laser treatment on the growth of a titanium oxide layer was evaluated using Energy Dispersive X-Ray Spectroscopy analysis. © 2019, The Author(s)

Fabrication of superhydrophobic and ice-repellent surfaces on pure aluminium using single and multiscaled periodic textures

Fabricating aluminium surfaces with superhydrophobic and ice-repellent properties present nowadays a challenging task. In this work, multifunctional structures are manufactured by direct laser writing and direct laser interference patterning methods using pulsed infrared laser radiation (1064nm). Diferent periodic patterns with feature sizes ranging from 7.0 to 50.0µm are produced. In addition, hierarchical textures are produced combining both mentioned laser based methods. Water contact angle tests at room temperature showed that all produced patterns reached the superhydrophobic state after 13 to 16 days. In addition, these experiments were repeated at substrate temperatures from −30°C to 80°C allowing to determine three wettability behaviours as a function of the temperature. The patterned surfaces also showed ice-repellent properties characterized by a near three-fold increase in the droplets freezing times compared to the untreated samples. Using fnite element simulations, it was found that the main reason behind the ice-prevention is the change in the droplet geometrical shape due to the hydrophobic nature of the treated surfaces. Finally, dynamic tests of droplets imping the treated aluminium surfaces cooled down to −20°C revealed that only on the hierarchically patterned surface, the droplets were able to bounce of the substrate.Fil: Milles, Stephan. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Technische Universität Dresden; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Voisiat, Bogdan. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemania. Fraunhofer Institute For Material And Beam Technology; Alemani

Hierarchical microtextures embossed on PET from laser-patterned stamps

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.Fil: Bouchard, Felix. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Baumann, Robert. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemani

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 recent years, substantial efforts have been made to develop new technologies capable to produce functionalized surfaces. One of these technologies is Direct Laser Interference Patterning (DLIP), 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 processing 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

Experimental measurement and numerical analysis of group velocity dispersion in cladding modes of an endlessly single-mode photonic crystal fiber

The optical properties of the guided modes in the core of photonic crystal fibers (PCFs) can be easily manipulated by changing the air-hole structure in the cladding. Special properties can be achieved in this case such as endless singlemode operation. Endlessly single-mode fibers, which enable single-mode guidance over a wide spectral range, are indispensable in the field of fiber technology. A two-dimensional photonic crystal with a silica central core and a micrometer-spaced hexagonal array of air holes is an established method to achieve endless single-mode properties. In addition to the guidance of light in the core, different cladding modes occur. The coupling between the core and the cladding modes can affect the endlessly single-mode guides. There are two possible ways to determine the dispersion: measurement and calculation. We calculate the group velocity dispersion (GVD) of different cladding modes based on the measurement of the fiber structure parameters, the hole diameter and the pitch of a presumed homogeneous hexagonal array. Based on the scanning electron image, a calculation was made of the optical guiding properties of the microstructured cladding. We compare the calculation with a method to measure the wavelength-dependent time delay. We measure the time delay of defined cladding modes with a homemade supercontinuum light source in a white light interferometric setup. To measure the dispersion of cladding modes of optical fibers with high accuracy, a time-domain white-light interferometer based on a Mach-Zehnder interferometer is used. The experimental setup allows the determination of the wavelengthdependent differential group delay of light travelling through a thirty centimeter piece of test fiber in the wavelength range from VIS to NIR. The determination of the GVD using different methods enables the evaluation of the individual methods for characterizing the cladding modes of an endlessly single-mode fiber

Picosecond laser interference patterning of periodical micro architectures on metallic molds for hot embossing

In this work, it is demonstrated that direct laser interference patterning (DLIP) is a method capable of producing microtextured metallic molds for hot embossing processes. Three different metals (Cr, Ni, and Cu), relevant for the mold production used in nanoimprinting systems, are patterned by DLIP using a picosecond laser source emitting at a 532 nm wavelength. The results show that the quality and surface topography of the produced hole-like micropatterns are determined by the laser processing parameters, such as irradiated energy density and the number of pulses. Laser-induced periodic surface structures (LIPSS) are also observed on the treated surfaces, whose shapes, periodicities, and orientations are strongly dependent on the accumulated fluence. Finally, the three structured metals are used as embossing molds to imprint microlenses on polymethyl methacrylate (PMMA) foils using an electrohydraulic press. Topographical profiles demonstrate that the obtained structures are comparable to the masters showing a satisfactory reproduction of the texture. The polymeric microlens arrays that showed the best surface homogeneity and overall quality were those embossed with the Cr molds.Fil: Fu, Yangxi. Technische Universität Dresden; AlemaniaFil: Soldera, Marcos Maximiliano. Technische Universität Dresden; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Wang, Wei. Technische Universität Dresden; AlemaniaFil: Voisiat, Bogdan. Technische Universität Dresden; AlemaniaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemania. Institut für Werkstoff-und Strahltechnik IWS; Alemani

Microfabrication and surface functionalization of soda lime glass through direct laser interference patterning

All-purpose glasses are common in many established and emerging industries, such as microelectronics, photovoltaics, optical components, and biomedical devices due to their outstanding combination of mechanical, optical, thermal, and chemical properties. Surface functionalization through nano/micropatterning can further enhance glasses’ surface properties, expanding their applicability into new fields. Although laser structuring methods have been successfully employed on many absorbing materials, the processability of transparent materials with visible laser radiation has not been intensively studied, especially for producing structures smaller than 10 µm. Here, interference-based optical setups are used to directly pattern soda lime substrates through non-lineal absorption with ps-pulsed laser radiation in the visible spectrum. Line-and dot-like patterns are fabricated with spatial periods between 2.3 and 9.0 µm and aspect ratios up to 0.29. Furthermore, laserinduced periodic surface structures (LIPSS) with a feature size of approximately 300 nm are visible within these microstructures. The textured surfaces show significantly modified properties. Namely, the treated surfaces have an increased hydrophilic behavior, even reaching a super-hydrophilic state for some cases. In addition, the micropatterns act as relief diffraction gratings, which split incident light into diffraction modes. The process parameters were optimized to produce high-quality textures with super-hydrophilic properties and diffraction efficiencies above 30%.Fil: Soldera, Marcos Maximiliano. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas. Universidad Nacional del Comahue. Instituto de Investigación y Desarrollo en Ingeniería de Procesos, Biotecnología y Energías Alternativas; ArgentinaFil: Alamri, Sabri. Fraunhofer Institute For Material And Beam Technology Iws; AlemaniaFil: Sürmann, Paul Alexander. Fraunhofer Institute For Material And Beam Technology Iws; AlemaniaFil: Kunze, Tim. Fraunhofer Institute For Material And Beam Technology Iws; AlemaniaFil: Lasagni, Andrés Fabián. Technische Universität Dresden; Alemani