Surface Functionalization (LiM 2021)

In-line monitoring of submicron laser texturing: a test bench for scatterometry
Aurélien Sikora, Alexandra Bourtereau, Rainer Kling, Girolamo Mincuzzi

Laser Induced Periodic Surface Structures (LIPSSs) with a submicronic periodicity induce a variety of surface properties (iridescence, hydrophobicity, antibacterial, etc.). In-line monitoring of LIPSS dimensions is challenging since the resolution of optical based microscopy techniques is insufficient or unable to withstand with harsh, industrial environment. These issues can be overcome using indirect measurement techniques such as scatterometry. It makes possible an indirect measurement of LIPSS morphology by analysing the reflection and/or diffraction pattern of an incoming light having a known spectrum and polarisation. We show that by using a proper configuration, scatterometry is barely sensitive to vibrations and fast enough for in-line monitoring fitting industrial requirements. In the frame of the NewSkin H2020 project, a scatterometer has been integrated and tested in a roll-to-roll machine including a fast polygon scanner (up to 200 m/s) and a 350 W femtosecond laser targeting mass production of LIPSS for antibacterial stainless steel.

Keywords: LIPSS; mass production; monitoring; scatterometry; femtosecond laser


Femtosecond laser structuring of nodular cast iron for anti-corrosion and thermally stable superhydrophobic surface
Dhiraj Kumar, Karla Kroechert Ching, Georg Kalss, Gerhard Liedl

The superhydrophobic surface has many applications, such as anti-corrosion, anti-icing, and self-cleaning. In this paper, we describe superhydrophobic surfaces on nodular cast iron produced by femtosecond laser pulses. A rapid transformation of surface characteristics from hydrophilic to superhydrophobic has been achieved after placing the samples in a high vacuum chamber for 10 hours, indicating a significant reduction in the storage time required to develop hydrophobic properties. Thermal stability has been assessed after heating the samples at different temperatures for an hour in a furnace. Consequently, the static contact angle has been measured after cooling at room temperature. Samples irradiated at 0.63 J/cm2 and 3.18 J/cm2 with a hatch distance of 20 μm show stable superhydrophobic characteristics up to 180°C. Corrosion tests have also been carried out on untreated and laser-treated samples at room condition in a 3.5% NaCl solution. Results indicate that a superhydrophobic surface has better resistance toward corrosion.

Keywords: Femtosecond laser; Superhydrophobic; LIPSS; Thermal stability; Corrosion


Towards optimization of femtosecond laser pulse nano-structuring for high-intensity laser matter interactions
Ulrich Teubner, Jürgen Imgrunt, Alexander Andreev

The interaction of intense femtosecond laser pulses with solid targets is a topic that has attracted large interest in science and applications. For many of the related experiments a large energy deposition or absorption and an efficient coupling to EUV- (extreme ultra violet, sometimes termed instead XUV) and/or X-ray photons and/or high energy particles is important. Here, beside improvements in laser pulse properties also those of the target are relevant. The present work investigates the formation of laser-induced periodic surface structures on massive metal targets by femtosecond laser pulses in vacuum. The experimental results and the ripple formation mechanisms have been analysed and interpreted with theoretical models. The present results contribute to a simple optimization of targets by nano-structuring their surface in-situ which leads to a significantly enhanced absorption and conversion efficiency into EUV emission, X-rays and/or high energy electrons and protons after irradiation with a subsequent intense laser pulse.

Keywords: LIPSS, ripple, high intensity femtosecond pulse, X-ray, EUV, XUV, high energy particles, proton acceleratio


Processing of an organosilazane-based glass/ZrO2 composite coating system by laser pyrolysis
Alexander Horcher, KatjaTangermann-Gerk, Günter Motz

Protective ceramic-based coatings are frequently the most suitable and cost-effective solutions for problems like corrosion, oxidation and wear. It has been shown, that the polymer-derived ceramics technology is suitable for the preparation of ceramic coatings by pyrolysis in a furnace. However, the required high temperatures for the preparation of the ceramic coatings only allow the use of temperature-resistant substrates. A very innovative approach to overcome this restriction is the use of laser radiation as an energy source for the pyrolysis of the preceramic polymer. For this reason, a composite coating system composed of an organosilazane with ZrO2 and glass particles as fillers was developed suitable for pyrolysis with a Nd:YVO4 laser. The composite coating slurry was applied onto stainless steel substrates by spraying and afterwards irradiated with a Nd:YVO4 laser. Finally, the microstructure, chemical composition, abrasions resistance as well as the mechanical properties and the corrosion behavior was investigated.

Keywords: Polymer-derived ceramic; Laser pyrolysis; Nd:YVO4 laser; environmental barrier coating


Improving the bond strength of metal-FRP-hybrids with thermal sprayed copper using pulsed laser-based processing approaches
Jana Gebauer, Volker Franke, Kevin Gustke, Thomas Lampke, Andrés Fabián Lasagni

Ablation processes during laser treatment of carbon fiber-reinforced plastics (CFRP) with pulsed lasers of various wavelengths and pulse durations are investigated. Three different surface pre-treatment strategies are used, including laser-roughening, selective matrix removal and laser micro structuring. Various ablation mechanisms, including evaporation and photochemical ablation are reported, depending on the employed laser source. Selected laser structured substrates were coated with copper by a wire arc spraying process. Bonding strengths up to 18.7 ± 2.0 MPa were achieved in shear tensile tests, by the combination of the roughening process and the micro-structuring approach. Consequently, the bonding strength could be increased over ~ 180 % compared to the common pre-treatment by mechanical blasting.

Keywords: Surface Functionalization; Pulsed Laser; Fiber-Reinforced Plastic; Metal-Plastic Hybrid; Coating Deposition


Laser polishing of laser micro weld seams on Cu-ETP and CuSn6 with green laser radiation
Moritz Küpper, Marc Hummel, Rakesh Kumar Pandey, Constantin Häfner

Copper and copper alloys used in electrical applications can be contacted by laser micro welding. The achievable roughness of these micro weld seams can be too large for some applications (like sealing surfaces or to minimize surface oxidation). Up to now laser polishing, which smoothens the surface due to surface tension in the molten state, of copper could not be demonstrated successfully with industry common infrared high power laser systems typically used for laser polishing. This study investigates the use of green 515 nm wavelength high power laser sources for laser polishing of pure copper (Cu-ETP) and a widely used copper alloy (CuSn6). A suitable process window is identified by variation of process parameters (laser beam diameter, scanning speed, laser power) for single and overlapping remelting tracks. The best parameters are tested on laser micro weld seams created with the same setup to smoothen their rough surface.

Keywords: laser polishing; laser micro welding; copper; CuSn6; green laser radiation


Fabrication of complex periodic patterns on a metallic drum forhigh throughput roll-to-roll processing
Bogdan Voisiat, Max Menzel, Wei Wang, Yangxi Fu, Marcos Soldera, AndrésFabián Lasagni

In this study, the development of complex periodic structures on massive metal drums by means of direct laser
interference patterning (DLIP) is demonstrated. The DLIP technology allows the formation of high-resolution periodical
structures (even with sub-micrometer resolution) at high fabrication speeds on large surface areas. These advantages
drastically reduce the patterning costs of the drums that are broadly used in roll-to-roll processing. We demonstrate the
ability to control individually each laser spot (e.g. period) to form complex periodical patterns to be used as decorative
elements exhibiting structural colors. These patterns are then replicated on a polymer foil by an industrial hot-embossing
roll-to-roll process at speeds up to 50 m/min. This process brings the industrial fabrication of such patterns to the next
level in terms of throughput and is thus suitable for mass production.

Keywords: Direct Laser Interference Patterning; roll-to-roll; structural coloration; diffraction gratings


Improvement of hardness and wear-resistance of direct laser interference patterned bearing steel surface using laser surface heating approach
Mikhael El-Khoury, Marko Seifert, Sven Bretschneider, Martin Zawischa, Tobias Steege, Sabri Alamri, Tim Kunze and Andrés Fabián Lasagni

In this work, we report on the laser heat treatment of periodic topographies produced on bearing steel plates using Direct Laser Interference Patterning (DLIP) technology. The hardening treatment allowed tuning the surface hardness from 210 to 827 HV. The combination of the patterning and laser hardening approaches permitted to improve the wear-resistance of the structured surface by ~ 50 % at contact point pressure of ~17.87 GPa. The outcomes indicated that by applying the proposed joined methodology it is conceivable to hold the higher hardness of the bearing steel plates and simultaneously to keep intact surface microstructures.

Keywords: Direct Laser Interference Patterning; laser surface hardening; wear; functional surfaces


Laser sintering of ceramic-based solid-state battery materials
Linda C. Hoff, Walter S. Scheld, Christian Vedder, Jochen Stollenwerk, Sandra Lobe, Sven Uhlenbruck

Solid-state batteries (SSB) can increase gravimetric energy density and safety compared to conventional lithium ion batteries. Possible materials for SSB are ceramic oxides, for example LiCoO2 (LCO) as cathode material and Li7La3Zr2O12 (LLZ) as electrolyte material. Due to the low ionic conductivity of the cathode material it is necessary to mix the cathode material with the electrolyte to generate a mixed cathode with higher ionic conductivity. Microparticle layers of cathode and electrolyte materials must be sintered to reach a functional and dense layer. A laser sintering process enables short interaction times at elevated temperatures. Therefore, diffusion processes and side phases could be reduced. In this work, mixed cathode layers consisting of LCO and LLZ were screen printed on steel substrates generating a direct contact to the current collector and afterwards laser sintered. Crystallographic investigations by x-ray diffraction revealed the existence of the desired phases (LLZ and LCO), while the densification was successfully observed by scanning electron microscopy. The adhesion of the layer to the substrate was proven by tape tests. A pyrometry based control of the laser power is implemented and different process temperatures are compared. Additionally, a thermal pre-heating on a hotplate was applied leading to an improved layer-substrate adhesion.

Keywords: solid-state battery; laser processing; laser sintering; electromobility;


Direct laser writing of metal nanostructures from the gas phase by two-photon-absorption process
Nicolai Schwarz, Michael Bassler, Thomas Walther, Thomas Klotzbuecher

A new approach for the generation of three-dimensional metal nanostructures, based on two-photon-absorption (TPA) of fs-laser radiation on silver-precursor molecules in the gas phase, is introduced. For that, a mode-locked fs-laser of 800 nm central wavelength and a pulse duration of 10 fs at a frequency of 76 MHz is used. The deposition process is performed in a vacuum chamber, allowing for evaporating a liquid organometallic silver-precursor under controlled temperature and pressure conditions. An inverse microscope objective of NA=0.65 and a working distance of 0.57 mm is used to focus the beam through a sapphire window onto a substrate, fixed in the vacuum chamber. The focus is moved in space by means of a piezo-driven stage with nm-resolution. Two-dimensional silver structures with dimensions in the sub-micrometer range are successfully deposited from the gas phase on glass substrates. Future investigations aim for extending the method into the third dimension.

Keywords: two-photon absorption; femtosecond laser direct writing; metallic nanostructures; gas-phase; silver precursor


The effect of chemical components on wettability at ps laser micromachined surface on stainless steel 304
Munehiro Chijiiwa, Niklas Berger, Mareike Schäfer, Rolf Merz, Michael Kopnarski, Peter Mitschang, Johannes A. L'huillier

Recently, controlling the wettability of metallic surfaces by laser micromachining has become important for many technical applications. However, there is still a challenge in understanding chemical effects on contact angle (CA) since there is even a big gap in knowledge of the laser micromachining’s influence on surface chemistry. In this study, the relationship between the local surface chemistry at ps-laser micromachined surfaces on stainless steel 304 and CA was discussed by using a new model description, based on a multiple regression analysis. The proposed model was verified by using the experimental wetting behavior of different kinds of liquid and surface chemistry, characterized by XPS spectroscopy. To have a variety of different wettability of the samples, different structures, storage conditions, and post processes were tested. As a result, our proposed model showed a nice correlation between predicted CA from chemical components and measured CA.

Keywords: wettability; ps laser; XPS; multiple regression analysis; surface functionalization;


Low temperature and high concentration laser doping system for fabrication of 4H-SiC power devices
Toshifumi Kikuchi, Takuma Yasunami, Akira Mizutani, Daisuke Nakamura and Hiroshi Ikenoue

We propose a high-concentration and low-crystal-damage doping method by irradiating deposited films with a KrF excimer laser containing dopant atoms on the 4H-SiC surfaces. This laser doping method is a low-temperature process that reduces the thermal stress on the substrate, and it can achieve a doping concentration of ~1020 cm-3 or higher, which exceeds the limit of the ion implantation method.
In this study, we investigated the peak energy dependence of the crystal damage and surface roughness by controlling the pulse width of the laser for doping. It was found that the crystal damage and surface roughness were reduced by suppressing the peak energy. In addition, we report on the construction of a laser doping system to improve the compatibility with the manufacturing process of 4H-SiC power devices.

Keywords: laser doping, power device, semiconductor, excimer laser, 4H-SiC;


Excimer laser annealing with a controlled grain size of poly-Si films for large display panels
Mizutani Akira, Hamano Fuminobu, Nakamura Daisuke, Goto Tetsuya, SitiRahmah Aidd, Ikenoue Hiroshi

Low-temperature polycrystalline Si (LTPS) thin-film transistors crystallized by excimer laser annealing (ELA) have been used as backplanes for active-matrix organic displays owning to their high mobility. However, the current ELA method requires a line beam with the major axis dimension equivalent to the minor axis of the substrate size, whereby limiting its applicability to large glass substrates. One solution to this problem is to anneal the entire surface of the substrate by folding back the beam; this process is referred to as the multi-scan annealing. However, in the overlapping region caused by the multi-scan annealing, the grain size increases, resulting in uneven device characteristics on the glass substrate. In this study, we annealed amorphous silicon by folding back the beam with an intensity distribution to observe the morphologies of grains in single and double scan region and to evaluate the mobility of the TFTs. As a result, it was demonstrated that uniform size grains could be formed in the single and double scan region, and that the dependence of mobility on the number of laser shots was low. In addition, the amount of change in mobility due to the presence of scan borders in TFT channel was clarified and it was shown that this can be attributed to misalignment of the stage.

Keywords: LTPS; TFT; laser annealing


Molded parts with functional surfaces – how laser microstructuring can be used for low-cost mass products
Maik Steinbach, Jürgen Koch, Peter Jäschke, Stefan Kaierle, Ludger Overmeyer

Microstructuring via ultrashort pulse laser enables the targeted generation of functional surface structures. With this technology, progress in material behavior has been shown in tribological, optical and haptical properties, liquid wettability and cell adhesion. In cases where the effect is mainly based on the laser-generated microstructures instead of laser-induced chemical changes of the surface material, injection molding offers a possibility to make the usually high-priced laser surface functionalization accessible to low-cost mass products. This technique leaves the chemistry of the molded parts unaffected, which makes it especially attractive for biomedical applications. Molding inverts the surface topography and can be associated with resolution, durability and demoldability restrictions. We present our current results and findings on basic as well as on application-oriented issues. Selected applications including a technique for piracy protection are discussed.

Keywords: microstructuring; surface functionalization; molding; ultrashort pulse laser


Enhanced forming behavior of conditioning lines by inserted microstructures for the production of 3D waveguides
Alexander Wienke, Mohd Khairulamzari Hamjah, Gerd-Albert Hoffmann, Jürgen Koch, Peter Jäschke, Jörg Franke, Ludger Overmeyer, Stefan Kaierle

In today's increasingly connected world, more and more data is being produced and processed. To meet these challenges, the OPTAVER research group is conducting research on an innovative manufacturing process for 3D waveguides. In this process, so-called conditioning lines are first printed onto a PMMA substrate by means of flexographic printing. Between those the waveguide is applied by aerosol-jet in a subsequent process. To achieve a three-dimensionality, thermoforming is used. If the degree of forming is too high, the conditioning lines crack and become unusable, because waveguide material accumulation due to the cracks leads to disadvantageous optical properties such as strong scattering and high attenuation. By inserting microstructures in the flexographic printing form at points where a high degree of forming is expected, material voids occur in the printing. These microstructures act as a predetermined breaking point, leaving the critical areas of the conditioning line untouched. This can significantly increase the 3D capability, as demonstrated in forming tests.

Keywords: Ablation; Functionalization; Femtosecond Laser; Enhanced forming behavior; Thermoforming Flexographic Printing; Printing Form


Targeting mass production of nano/micro textured surfaces by USP laser: the New Skin project
G. Mincuzzi, A. Bourtereau, M. Faucon, L. Gemini, S. Nourry, A. Sikora, R. Kling

Ultra-Short Pulse laser texturing (USP-LT) is a key technology for functionalisation of materials surface. Although the texturing of ≈1m2 surfaces have been successfully shown, extend USP-LT over several m2 surfaces represents an issue due to the need of high P, and a difficult process control. The “New Skin” project could represent a turning point pushing the readiness of USP-LT with a significant up-scale of the production volume. Here we show the preliminary results obtained with the implementation of a demonstrative pilot line based on a 350 W, fs laser and a polygon scanner. We report the optimisation of the structures morphology on steel when P exceeds few hundreds of watts as well as the impact of the repetition rate (up to 10 MHz) and the hatch. A roll-to-roll approach is proposed jointly with an in-line monitoring system based on scatterometry. Finally, possible applications and values propositions are introduced and discussed.

Keywords: surface texturing, roll-to-roll processing, large surface texturing, ultrashort pulse lasers, New Skin project;


Structural coloration and wettability control of stainless steel by a DLIP process
T. Delgado, C. Alleaume, S. M. Vidal, F. J. Gontada, F. Ares, P. Romero, N. Otero

We present the use of a Direct Laser Interference Patterning (DLIP) setup to modify both optical and wettability properties of stainless steel by a laser surface texturing process. In particular, a two-beams DLIP setup was employed to engrave periodic line-like textures with two different periods on the surface of stainless steel samples. The engraved textures acted as a diffraction grating, allowing the structural coloration of the stainless steel; while achieved a hydrophobic behaviour after applying a post-thermal treatment.

Keywords: DLIP; surface texturing; stainless steel; wettability; optical properties


Laser-based coating process of PA12 on stainless steel substrates
Alexander Wittmann, Oliver Hentschel, Jakob Ermer, Alexander Sommereyns, Florian Huber, Michael Schmidt

Thermoplastic polymers are of great interest for functional coatings due to their good material properties (e.g. chemical and wear resistance, biocompatibility). In the presented study, a laser-based coating process for polyamide 12 (PA12) powder on stainless steel substrates was investigated. To evaluate the influence of the wavelength on the resulting coating characteristics, ytterbium (λ = 1.07 μm) and thulium fiber laser (λ = 1.94 μm) were compared for the consolidation of the deposited PA12 powder. Optical microscopy analyses were conducted to characterize the coatings. Furthermore, the degree of particle melt was investigated by differential scanning calorimetry. Results show that dense and adherent coatings can be applied on stainless steel substrates. As the PA12 powder reveals a lower absorption at the wavelength of 1.07 μm, PA12 particles were partially melted by the ytterbium fiber laser. In case of thulium fiber laser, a substrate heating is a crucial process parameter to improve wetting as well as adhesion.

Keywords: laser polymer deposition; thulium fiber laser; ytterbium fiber laser; polymer coating; PA12


Metallic surface functionalization by femtosecond laser beam shaping and LIPSS for industrial applications
Jérôme Patars, Liliana Cangueiro, Anthony Kirsch, David Bruneel, J.A. Ramos-de-Campos

Literature demonstrated the advantages of surface nanoscale texturation in many industrial applications, including batteries, medical implants and linear encoders. The next step is to find a cost-effective and non-invasive solution to replace actual material deposition and tooling techniques at industrial scale.
In the scope of the LASER4SURF project, we developed a new automated workstation enabling fast texturing of large surface samples (i.e. A4 format), using state of the art beam shaping techniques involving DOE and SLM combined with LIPSS generation to increase functionalization performances of the textured materials.
A key part of the workstation is its ability to automatically determine optimal laser processing parameters based on preliminary study done on any other laser processing device.
We also demonstrate that LIPSS texturation increases battery collectors charging capabilities, as well as their lifetime. We also demonstrate better bio-integration of medical implant for the human body, as well as increased accuracy linear encoders.

Keywords: Femtosecond laser ; surface texturing ; surface functionalisation ; beam-shaping


Superhydrophobic surfaces using ultra-short pulse structuring of thin metals
Fabian Schaefer, Simon Ruck, Max-Jonathan Kleefoot, Wadim Schulz, Florian Köhn, Joachim Albrecht, Harald Riegel

Fabrication of superhydrophobic surfaces induced by ultra-short-pulse lasers is a hotspot of surface studies. We report a way of generating superhydrophobic surfaces on stainless steel (304S15). The method for fabricating this water-repellent surface is to microstructure by irradiating with ultra-short-pulses.
Contact angle measurements were used to investigate the wettability of the surface in relation to the laser parameters (laser fluence and scan line separation). The steady contact angle was investigated in the range of 140°. Investigations with optical measuring methods (white light interferometer) displays the structures of the surfaces. The generated surface shows hierarchical structures with nano and micro roughness similar to a lotus leaf. In further experiments, different materials shall be sputtered to obtain a thin stainless steel layer. Subsequent laser structuring should produce a functional surface with water repellent properties

Keywords: superhydrophobic surfaces; laser structuring; ultra short pulse; sputtering; stainless steel


Laser based 3D-magnetic field sensor formation
Markus Müller, Mandy Gebhardt, Hans-Ulrich Zühlke

A world with intelligent electronic devices in every machine and every pocket needs a wide range of sensor technologies. One rapidly growing technology is the sensing of magnetic fields, which can be used in numerous industrial applications such as the angular detection of the precise position of a steering wheel in a car, the measurement of position and interaction of objects for Internet of Things (IoT) applications, the contactless detection of electrical currents, and position detection by e-compass for many different mobile devices including virtual reality (VR) systems, etc. Very sensitive magnetic sensor chips can be realized by using GMR or TMR (Giant or Tunneling magnetoresistance) sensors in a Wheatstone bridge circuit built in a monolithic design.
This presentation gives an overview of the design, function, operation, and production results for a laser-based annealing technology, which enables the programming of advanced sensor structures at the wafer level. The key feature is the combination of a selective laser spot with a local, in-situ rotatable magnetic field. The laser spot heats up exactly one sensor area while the magnetic field with the correct orientation is applied.

Keywords: laser annealing; monolithic integrated magnetic sensors; microVEGA xMR; Giant Magneto-Rresistance Sensor; Tunneling Magneto-Resistance Sensor; GMR; TMR


Effect of confined laser plasma plumes on the formation of LIPSS structures on stainless steel 316L
Anupam Ghosal, Olivier Allegre, Zhu Liu, Gordon Jones

Laser-induced periodic surface structures (LIPSS) has been used for functionalisation of stainless steel surfaces. Hence, the control of the formation of the LIPSS structures is an essential aspect of laser surface texturing. In this work, picosecond pulsed laser irradiation (wavelength 355nm, pulse duration 10ps, frequency 404.7 kHz) was performed on stainless steel 316L under confined laser plasma plumes in atmospheric condition. The plasma plumes generated due to laser-metal interaction were confined by covering the metal surface with a transparent glass plate at varying distances (Δz = 0, 300, 450, 900 μm). The effect of the gap between metal and glass surface towards the formation of uniform LIPSS was studied experimentally. High spatial frequency LIPSS (HFSL) was produced by controlling the gap width. Low-spatial-frequency-LIPSS (LSFL) was observed at higher fluence along with scattered metal deposits on the surface. This work demonstrated the possibility of creating uniform HSFL using confined laser plasma plumes as the impacting medium.

Keywords: Laser-induced periodic surface structure (LIPSS); Nanostructure; Picosecond pulsed laser; Surface topography; laser plasma plume, high-spatial-frequency-LIPSS (HSFL)


Laser melt injection for homogenous particle distribution in copper materials
Anika Langebeck, Annika Bohlen, Thomas Seefeld

MMC (metal matrix composite) layers have great potential to improve abrasive wear resistance of tool surfaces such as injection molds. For this, laser melt injection is used to disperse hard particles into the molten tool surfaces. By varying the process parameters a non-homogenous particle distribution can occur. This paper addresses the systematic study to evaluate the influence of the process velocity and the powder feed rate on the particle distribution of spherical fused tungsten carbide in aluminum bronze. It is shown, that with increasing powder feed rate and decreasing process velocity a homogenous particle distribution can be achieved. The process velocity is identified as a major affecting parameter on the particle distribution. For the analyzed MMC system a process velocity of 300 mm/min led to a homogenous distribution whereas faster process velocities of 500 mm/min resulted in a graded particle distribution.

Keywords: laser melt injection; MMC; aluminum bronze; spherical fused tungsten carbide


Excimer laser sintering of ceramic thin films for solid state batteries
Matthias Trenn, Linda C. Hoff, Ralph Delmdahl, Matthias Greiber, Karsten Lange, Christian Vedder

The geopolitical dependence on limited fossil resources and the increasing number of environmental disasters are enormous challenges for today’s society. An important element to overcome these essential problems is to increase the performance of energy storage systems and the efficiency of energy conversion devices. A promising solution are ceramic solid-state batteries providing a high level of safety and energy density. One of the challenges on the way to high volume production is the demand of a temperature-sensitive thin-film sintering process step, where the conventional sintering process is limited. The production of solid-state batteries demanding high standards on new production technologies. In this paper, a new highly scalable excimer laser-based sintering process of ceramic thin films is presented. The nanosecond pulses selectively melt the material at the surface of the powder grains. Due to the short 248 nm laser wavelength, sintering depths of only 4 - 8 μm can be achieved. In the process, the crystalline phase of the powder and thus also the electrochemical properties of the layer are retained.

Keywords: excimer laser; thin film sintering; ceramic sintering; solid-state batteries; large-area processing


Surface carbon enrichment of stainless steel using nanosecond pulsed laser surface alloying of a graphite based coating
H. Mustafa, M. Feinaeugle, G.R.B.E. Römer

Laser surface alloying is a promising technique for modifying and/or improving surface properties of forming tools used in the fabrication of thermoplastic composite parts. The results of a study on laser surface alloying of graphite based coatings on ferritic stainless steel using a nanosecond pulsed laser source is presented. The effect of different laser processing parameters and coating types on the laser-induced carbon diffusion in the steel are analyzed. The morphology of the processed areas was characterized using confocal microscopy and scanning electron microscopy. The atomic concentration of diffused carbon was determined using energy-dispersive X-ray spectroscopy. It was found that the surface carbon content of stainless steel can be increased substantially up to 70% in weight. Cross-sectional analysis revealed the dependence of diffusion thickness on the accumulated laser fluence, having a maximum depth of about 6.5 μm. In comparison to low and high carbon steel, and unprocessed stainless steel, laser processed samples demonstrated improved wear properties.

Keywords: Laser surface alloying; carbon enrichment; stainless steel; nanosecond laser


Ultrashort laser coloration on metallic coatings
E. Rodríguez-Vidal, G. Alberdia, B. Coto, O. Fernández, J.Lambarri, A. Ribera

This study reports on the fabrication of structural and intrinsic color from the oxide layer layers via ultrashort pulses on three different metallic coatings deposited on glass substrate. Surface modifications are tuned by adjusting laser fluence deposited on metallic coating. Thickness up to 0.4μm of titanium (Ti), and Chromium (Cr) were deposited on borosilicate substrates by physical vapor deposition. A comprehensive study of the physical and chemical measurements leading to the different appearance is presented. Different physical modifications, at micro and nanoscale levels, were identified depending on laser processing conditions. Uniform and repetitive color palette on Ti and Cr was developed by femtosecond pulses.

Keywords: Ultrashort laser pulses; metallic coatings; coloration; nanopatterns


Friction reduction of stainless steel surfaces by laser microstructuring
Niklas Berger, Benjamin Keim, Munehiro Chijiiwa, Hicham Derouach, Senta Schauer, Mareike Schäfer, Johannes A.L’huillier

Recently, friction reduction has become important in a wide range of technical applications. One limiting factor is the abrasion of two surfaces when they are moved against each other, causing friction losses. To overcome this, a functional optimization is necessary and thus the effectiveness of components will be increased by structuring the surfaces. Our approach is to introduce a dimple structure by laser microstructuring into the surface and thus significantly reduce the friction. In order to avoid burr around these dimples, it is necessary to operate good heat management. For this reason, we carried out experiments using a USP laser with a pulse duration of 10 ps. Dimples with a diameter of 10 – 30 micrometers were made and systematic investigations were carried out by changing the depth and the arrangement of the dimples. By optimizing these parameters, friction could be reduced by 30 % compared to an unstructured surface.

Keywords: friction; dimples; picosecond-laser; microstructure


Improved thermal joining of aluminum and aluminum-polymer-composites for battery applications through laser surface structuring
Christian Geiger, Lucas Hille, Célestine Singer, Michael F. Zaeh

Lithium-ion batteries are the major electrochemical energy storage solution for electromobility applications because of their advantageous characteristics (e.g. specific energy and energy density) compared to other battery technologies. Cur-rently, mostly three cell designs (prismatic hardcase cells, prismatic pouch cells and cylindrical cells) with different ad-vantages and disadvantages are present in the market. Novel cell concepts were developed to combine the strengths of the available cell designs, e.g. the good mechanical stability of hardcase cells and the high gravimetric energy density of pouch cells. Hybrid cell designs based on aluminum-polymer-composite foils and aluminum are a promising approach. In this paper, a laser structuring process is presented, which significantly improves the adhesion between thermally joined aluminum-polymer-composite foils and solid aluminum. Microscopic structures were formed on the aluminum surface by nanosecond laser pulses. The results of a laser parameter study were analyzed optically in terms of surface roughness by laser scanning microscopy and mechanically by adhesion strength tests. Based on that, strategies for the laser structuring process were derived.

Keywords: laser structuring; lithium-ion batteries; battery casing; aluminum; aluminum-polymer-composite


Manufacturing of functional surfaces by replicating glass moulds structured by multiphoton polymerization.
Sara M. Vidal Álvarez, Francisco José Gontad Fariña, Nerea Otero Ramudo, Felix Ares Blanco, Maria Ivette Coto Moretti, Tamara Delgado García, Pablo Romero Romero

The present work deals with the fabrication of very low aspect ratio microstructures generated by Multi-Photon Polymerization (MPP) on glass substrates for their further use as good quality and high resolution replication moulds for optoelectronic devices. A commercial UV-curable resin from the ORMOCER® family was employed for the fabrication of the polymeric microstructures on two different substrates: glass and sapphire. These microstructures were replicated by injection (IM) moulding on polymeric components with an area of several cm2. The results of this work indicate that high resolution moulds can be fabricated through MPP, favouring the fabrication of high-quality replications. Additionally, the microstructures are proven to be resistant to their use through multiple replications. In fact, the topographical characterizations of the first and last replicas show similar characteristics, proving the reliability MPP for the fabrication of high quality moulds.

Keywords: Multiphoton polymerization, femtosecond laser, replication, injection moulding, optical surfaces.


Laser texturing of heat exchanger tubes for nucleate boiling regime promotion
Félix Ares, Ivette Coto, Nerea Otero, Sara Vidal, Tamara Delgado, Francisco Gontad, Roberto Eiró, Pablo Romero

Titanium tubes of 16 mm diameter and 0.8 mm thickness, were textured using a cw, single mode, 1070 nm fibre laser. The laser beam was guided by a galvanometer scanner. Textures of homogeneous, parallel grooves of 60-80 μm width and 70-110 μm depth were generated on the exterior tubular surface. A wide range of parameters: laser power, laser speed, tube rotating speed or focal distance was studied to improve the homogeneity of the generated textures. These tubes were later tested in both controlled and industrial environments, along with non-textured tubes, and their heat transfer behaviour was analyzed under an ammonia nucleate boiling regime. Results indicate that laser textured tubes show a consistent increase of 60 % of their heat transfer coefficient, when compared to original smooth tubes. These results prove that laser texturing is a suitable technique to significantly increase performance of heat exchangers that work under nucleate boiling regime.

Keywords: Laser texturing; heat exchanger; nucleate boiling; continuous wave; tubular surfaces; microprocessing;


Improved catalytic activity and surface functionalization of nanoparticles by pulsed laser post-processing of colloids.
Sven Reichenberger, Swen Zerebecki, Stephan Barcikowski

The precise writing of defects and structural alterations into colloidal nanoparticles offers a great application potential. To that end, many studies using pulsed laser post-processing were conducted in the past. Yet, either multi-pulse phenomena and/or intensity gradients linked to the experimental setup rendered gradual and uniform tailoring of material properties complicated. In the presented article a new setup that provides a thin flat liquid jet for continuous laser post-processing of nanoparticles with single laser pulses is presented and discussed. As will be shown, compared to the conventional liquid jet setup with circular cross-section, the new flat jet realizes unprecedented uniformity of laser excitation conditions, significantly decreasing laser intensity deviations. Due to the higher uniformity of the laser treatment, the fragmentation threshold of gold nanoparticles was experimentally evaluated with high resolution and very good agreement with the theoretical prediction. For the conventional liquid jet setup, no threshold was observed. This new uniform laser post-processing of colloidal nanoparticles holds great potential for all applications requiring a tailored design of defect density and materials properties.

Keywords: pulsed laser post-processing of nanoparticles, laser fragmentation, catalysis, metal nanoparticles


Laser-assisted selective fabrication of copper traces on polymers by electro-plating
Vitalij Fiodorov, Karolis Ratautas, Zenius Mockus, Romualdas Trusovas, Gediminas Račiukaitis

Selective deposition of metals on dielectric materials is widely used in electronic industry, making electro-conductive connections between circuit elements. We report a new low-cost laser-assisted method for selective deposition of copper tracks on polymer surfaces by electro-plating. The technique uses a laser for selective modification of polymer surface. The electrical conductivity of some polymers could be increased due to laser irradiation. Polyimide (PI) Kapton® film was used in our experiments. Samples were patterned using nanosecond and picosecond lasers working at the 1064 nm wavelength. The experiments were performed using average powers ranging from 4 to 8.5 W in 0.25 W increments, pulse repetition rates from 10 to 100 kHz and a constant scanning speed of 100 mm/s. The sheet resistance was measured using the four-probe method, and it was reduced to < 10 Ω per square after the laser patterning. Analysis of Raman spectra of specimens patterned areas were performed. Afterwards, different thicknesses of copper layer were deposited on the modified surface by electro-plating.
Our selective laser-assisted technology allows fabrication of copper tracks on complex shape dielectric materials. The technology could be used in production of molded interconnect devices (MID), where the main technological problem and achievable task is the low cost fabrication of copper tracks.

Keywords: laser, electro-plating, polymer, deposition;


High-rate laser machining for large-area and high-throughput surface profiling and functionalization
Joerg Schille, Stefan Mauersberger, Andreas Gruner, Lutz Schneider, Kristian Kujawa, Udo Loescher

High-rate laser machining will be introduced as key technology for large-area surface texturing and bio-inspired functionalization. In fact, the polygon-mirror based scan technique allowing high-precision laser beam raster-scanning at hundreds meters per second is the core feature to bring high optical powers from kilowatt class lasers to industrial production. This is favorable for power scaling in micro machining as processing rate and throughput scale-up with higher pulse repetition frequency and laser powers. The great advantage of ultrafast beam movements is that unfavorable effects can easily be avoided, such as high thermal loads to the substrates and subsequent material melting as well as laser beam shielding by interactions with the previously induced plasma/particle plume. Inspired by sharks´ skin, this will be demonstrated by the example of riblet-like surface profiles and their replications in plastic materials thus providing a high potential for drag reduction in turbulent flows in technical applications.

Keywords: High power lasers; laser micromachining; laser scanning