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The present work utilizes Direct Laser Interference Patterning (DLIP) to impart periodic microstructures onto the surface of nickel foils. A pulsed laser source emitting green radiation (514 nm) with pulse duration between 282 fs and 1 ps is utilized to produce line and cross-like pattern geometries having a spatial period of 3.0 µm and a maximum structure depth of ~ 2.8 µm. Both the pulse duration and number of consecutive scans are varied in order to assess their influence on the structure formation. Afterwards, the treated Ni- electrodes are used for alkaline water electrolysis. The most active electrode exhibits an overpotential of -227 mV at a current density of -0.5 A cm-2 for the Hydrogen Evolution Reaction (HER). Thus, the technique here proposed permitted a 51 % reduction in the overpotential of the HER compared to the untreated Ni-electrode, opening up possibilities for the development of more efficient electrodes for hydrogen production. [ABSTRACT FROM AUTHOR]

This study investigates the influence of processing parameters when applying direct laser interference patterning (DLIP) on the morphology and microstructure of zirconia surfaces using a 10 ps‐pulsed laser source with 1064 nm wavelength. An experimental testing matrix is built with different values of laser fluence (5.7–18.2 J cm−2) and pulse overlap (66–98%). Surface morphology and microstructure are characterized by confocal microscopy and scanning electron microscopy. Homogeneous line‐like patterns with periodic spatial repetition of 5.0 µm, with varying depths, widths, and aspect ratio, are fabricated using proper processing parameters (5.7–7.6 J cm−2 and 92–96%). Structures with maximum depth of 1.5 µm and sharp edges are obtained (7.6 J cm−2 and 96% overlap). Ablated regions presented a morphology typical of photophysical ablation mechanism, with signs of molten material at the surface. Sub‐micrometric pores and nanodroplets are registered for all conditions, while sub‐micrometric cracks developed only for higher fluences. A processing window conducing to homogenous DLIP structures is set based on experimental data. Periodic structures with multiscale topographic features are successfully obtained on zirconia surfaces using DLIP technology in this study. These outcomes open new perspectives for fabrication of multifunctional zirconia surfaces for advanced biomedical and engineering applications. [ABSTRACT FROM AUTHOR]

The aim of this work was to evaluate the feasibility of the fabrication of microtextures in zirconia using the direct laser interference patterning (DLIP) technique. A green ultra‐short pulsed laser (532 nm, 10 ps) with a two‐beam interference setup was used to produce line‐like structures with a spatial period of 3 µm. For a fixed set of fluence and pulse‐to‐pulse overlap values (6.2 J/cm2, 81%), periodic structures were successfully created for different hatch distances. The average depth of the features ranged from 0.37 µm for a hatch distance of 14.4 µm up to 0.84 µm for a hatch distance of 12.4 µm. However, a further decrease in hatch distance did not result in an increase in depth since the region of the ridges is also ablated. Scanning electron microscopy analysis showed pores formation on the laser grooves, but no sign of micro‐cracking could be observed. Wettability tests showed an increase in hydrophobicity after DLIP. These results bring exciting perspectives on the fabrication of micro‐textures with DLIP on zirconia surface. [ABSTRACT FROM AUTHOR]

Process monitoring in laser‐based manufacturing has become a forward‐looking strategy for industrial‐scale laser machines to increase process reliability, efficiency, and economic profit. Moreover, monitoring techniques are successfully used in laser surface texturing workstations to improve and guarantee the quality of the produced workpieces by analyzing the resulting surface topography. Herein, dot‐like periodic surface structures are fabricated on stainless steel samples by direct laser interference patterning (DLIP) using a 70 ps‐pulsed laser system at an operating wavelength of 532 nm. A scatterometry‐based measurement device is utilized to indirectly determine the mean depth and spatial period of the produced topography by analyzing the recorded diffraction patterns. As a result, the average depth and the spatial period of the dot‐like structures can be estimated with a relative error below 15% and 2%, respectively. This new process monitoring approach enables a significant improvement in quality assurance in DLIP processing. [ABSTRACT FROM AUTHOR]

In this work, the technique of Direct Laser Interference Patterning (DLIP) was used to fabricate micrometric structures at the surface of Cobalt-Chromium-Molybdenum and AZ91D magnesium alloys. Line-like patterns with spatial periods of 5 μm were textured using an ultra-short pulsed laser (10 ps pulse duration and 1064 nm wavelength) with a two-beam interference setup. The surface topography, morphology, and chemical modifications were analysed using Confocal Microscopy, Scanning Electron Microscopy, and Energy Dispersive Spectroscopy (EDS), respectively. Laser fluence and pulse overlap were varied to evaluate their influence on the final structure. Homogeneous structures were achieved for the CoCrMo alloy for every condition tested, with deeper structures (up to 0.85 μm) being achieved for higher energy levels (higher overlap and/or fluence). For high energy, sub-micrometric secondary structures, so-called LIPSS, could also be observed on the CoCrMo. The EDS analysis showed some oxidation after the laser texturing. Regarding the AZ91D alloy, deeper structures could be achieved (up to 2.5 μm), but more melting and oxidation was observed, forming spherical oxide particles. Nonetheless, these results bring new perspectives on the fabrication of microtextures on the surface of CoCrMo and AZ91D using DLIP. [ABSTRACT FROM AUTHOR]

In this study, a scatterometry-based monitoring system designed for tracking the quality and reproducibility of laser-textured surfaces in industrial environments was validated in off-line and real-time modes. To this end, a stainless steel plate was structured by direct laser interference patterning (DLIP) following a set of conditions with artificial patterning errors. Namely, fluctuations of the DLIP process parameters such as laser fluence, spatial period, and focus position are introduced, and also, two patterning strategies are implemented, whereby pulses are deliberately not fired at both deterministic and random positions. The detection limits of the system were determined by recording the intensities of the zero, first, and second diffraction order using a charge-coupled device (CCD) camera. As supported by topographical measurements, the system can accurately calculate spatial periods with a resolution of at least 100 nm. In addition, focus shifts of 70 µm from the optimum focus position can be detected, and missing patterned lines with a minimum width of 28 µm can be identified. The validation of this compact characterization unit represents a step forward for its implementation as an in-line monitoring tool for industrial laser-based micropatterning. [ABSTRACT FROM AUTHOR]

Advanced polymeric materials, such as polyether ether ketones (PEEK), have been placed as direct substitutes for metals and ceramics in diverse applications, such as the machinery industry and biomedical engineering. Moreover, surface treatments allow the emergence of brand‐new properties or the improvement of preexisting ones, such as friction, lubrication, wettability, cellular infiltration, or osseointegration. A paramount approach to achieving topographical modifications is by using laser micro/nanoprocessing techniques such as direct laser interference patterning (DLIP). Herein, PEEK foils are structured with DLIP method using ultrashort pulses. The influence of the pulse duration between 266 fs and 15 ps and the pulse‐to‐pulse overlap on the resulting surface topography and chemistry is assessed. As a result, well‐defined line‐like textures with a period of 5.8 μm and aspect ratios up to 0.88 are achieved. Furthermore, it is possible to explore and understand the behavior of surface phenomena such as swelling, increase/decrease of laser–material interaction onset, and laser‐induced periodic surface structures formation. A comprehensive topographical and chemical characterization study demonstrates that these distinctive topographical features occur because of multiphoton absorption, incubation effects, and heat accumulation. These phenomena allow structuring polymeric substrates that are low‐absorbing and challenging to pattern with conventional nanosecond infrared (IR) laser sources. [ABSTRACT FROM AUTHOR]

The functionalization of zirconia surfaces by accurate and fast printing of periodical patterns embedding sub‐micrometric features is of great interest to many engineering fields and is yet to be explored. This study aims to assess the influence of the Direct Laser Interference Patterning processing parameters on the morphology and microstructure of zirconia surfaces using a 532 nm 10 ps‐pulsed laser source. Well‐defined linear structures with a period of 3 µm are successfully produced. Depending on the laser parameters, the structures are developed at or below the surface level, with higher depths (≈1 µm) being seen for increasing values of laser fluence and pulse overlap. Line‐like hierarchical structures with smaller interference spatial structures (3 µm period) and higher secondary structures with different periods (18, 15, and 12 µm) and heights (7, 5, and 3 µm, respectively) are also obtained on zirconia surface. Ablated regions presented few traces of molten material, nano‐droplets, and sub‐micrometric (<1 µm) pores, while no (sub) micrometric cracks are detected. A slight amount of tetragonal to monoclinic phase transformation (≈5%) is detected by X‐ray diffractometry. A processability map for ps‐laser processing of zirconia is proposed based on the experimental data. [ABSTRACT FROM AUTHOR]

In this work, we report about the fabrication of textured aluminium surfaces using Direct Laser Interference Patterning with picosecond (70 ps) and femtosecond (400 fs) laser pulses as well as their wetting properties. The structuring process was performed by varying the pulse numbers from 25 to 250, resulting in various depths ranging from 0.9 µ m to 6.8 µ m. The wetting analysis shows that the ps-patterned surfaces exhibit long-term superhydrophobic characteristics (at 21 °C and 16 % air humidity). Differently, for the fs-processed substrates, a hydrophobic character was firstly observed, which later (after 16 days) dropped to contact angles similar as the untreated material. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The inversion of the laser intensity profile by polarization control was demonstrated. • Detailed theoretical and experimental analysis of the formed profiles are performed. • The pillar formation using the inverted interference intensity profile was shown. • The growth of the pillar with additional laser pulses was demonstrated. • The mechanism of the structures formations is discussed in details. Abstract Three-beam laser interference patterning, with the ability to control the polarization of each beam, is used to produce crater and pillar like periodic structures on steel surfaces. The experiments are performed using parallel and radial polarization vector orientations of the interfering beams. In case of parallel vector orientation, common intensity profiles consisting of intensity peaks distributed in triangle lattice geometry are formed. By changing the polarization to the radial set, the intensity distribution of the interference pattern could be inverted while the geometry also has a triangle lattice shape. The equations describing both intensity profiles are derived from the basic interference equation and the modeled interference intensity profiles are compared with measured intensity profiles. Two different types of structures containing periodically distributed craters and pillars are produced using these polarization sets. Using a detailed analysis of the scanning electron microscope images and confocal data, the mechanisms responsible of the formation of the pillar- and crater-like geometries are introduced. [ABSTRACT FROM AUTHOR]

This review investigates the capabilities of laser-based interferometric methods for producing structures with multiple-scaled surface features imitating natural examples. Firstly, laser interference lithography is used to produce hierarchical patterns with length-scales in the micrometer and sub-micrometer range. Different strategies are discussed to produce a wide variety of periodic arrays, depending on the number of resist lasers used as well as the way in which the exposure steps are organized. After that, periodic patterns are fabricated on polymers using ns laser pulses from an UV-laser system. Additionally in this case, multiple-scale patterns are produced by using different strategies. A similar approach is described to treat metallic surfaces of steel X6Cr17 and a titanium alloy Ti6Al4V. The geometry of the produced microstructures was characterized using scanning electron microscopy and confocal microscopy. Measurement of water contact angle is performed for both polymer and metallic surfaces. [ABSTRACT FROM AUTHOR]

Direct laser interference patterning (DLIP) is used to create periodic crater‐ and pillar‐like patterns on titanium surfaces. A Nd:YAG laser operating at 532 nm wavelength with a pulse duration of 8 ns and the ability to control the polarization of each individual beam is used for the laser patterning process. The generated periodic patterns with spatial periods of 5 and 10 μm are produced with energy densities between 0.3 and 5.1 J cm−2 with a single laser pulse. By varying the polarization of each interfering beam and the energy density, various forms of the occurring topography are observed due to the different shape of the interference intensity pattern and the solidification front of the molten material at the maxima positions. The characterization of the surface chemistry shows that the laser treatment increases the relative content of alumina in the reactive layer from 36% to 51%. The structural analysis of pillar‐like patterned surface shows no changes in microstructure after the laser treatment. Contact angles of 47° ± 7° down to 6° ± 4° are measured on both, crater‐ and pillar‐like surfaces which are significantly lower compared to the untreated reference (79° ± 2°). [ABSTRACT FROM AUTHOR]

Superhydrophobic natural surfaces usually have multiple levels of structure hierarchy, particularly microstructures covered with nano-roughness. The multi-scale nature of such a surface reduces the wetting of water and oils, and supports self-cleaning properties. In this work, in order to broaden our understanding of the wetting properties of technical surfaces, biomimetic surface patterns were fabricated on stainless steel with single and multi-scale periodic structures using direct laser interference patterning (DLIP). Micropillars with a spatial period of 5.5 µm and a structural depth of 4.2 µm were fabricated and covered by a sub-micro roughness by using ultrashort laser pulses, thus obtaining a hierarchical geometry. In order to distinguish the influence of the different features on the wettability behavior, a nanosecond laser source was used to melt the nano-roughness, and thus to obtain single-scale patterns. Then, a systematic comparison between the single- and multi-scale structures was performed. Although, the treated surfaces showed hydrophilic behavior directly after the laser treatment, over time they reached a steady-state hydrophobic condition. However, the multi-scale structured metal showed a contact angle 31° higher than the single-scale geometry when the steady-state conditions were reached. Furthermore, the impact of the surface chemistry was investigated by energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analyses. Finally, a hydrophobizing agent was applied to the laser treated samples in order to further enhance the water contact angles and to determine the pure contribution of the surface topography. In the latter case, the multi-scale periodic microstructures reached static contact angles of 152° ± 2° and a contact angle hysteresis of only 4° ± 2°, while the single-scale structures did not show superhydrophobic behavior. These results definitely suggest that multi-scale DLIP structures in conjunction with a surface chemistry modification can promote a superhydrophobic regime. [ABSTRACT FROM AUTHOR]

[Display omitted] • Periodic structures are produced on PEEK using DLIP using a 1064 nm ps laser. • Shape and height of structures can be controlled by varying the cumulated fluence. • Structures were produced with depth values up to ∼2.5 µm and aspect ratio of ∼0.5. • Secondary structures (LIPSS, p ≈ 1 µm) perpendicular to main pattern were observed. In this work, we aimed at getting the first insight into the influence of the laser processing parameters on the production of functional multi-scale PEEK surfaces using the Direct Laser Interference Patterning technology. An infrared ultra-short pulsed laser source (1064 nm, 10 ps) and a two-beam interference setup were used. The fabricated structures morphology was analyzed by Scanning Electron Microscopy and Confocal Microscopy. As a result, line-like structures with periodic spatial repetition (p) at two levels were produced: main structures with p = 5 µm and mean depth values up to ∼2.5 µm (aspect ratio of ∼0.5) and secondary structures, perpendicularly oriented relative to the main structures, formed at DLIP maxima position (top part of ridges) with p ≈ 1 µm (LIPSS). [ABSTRACT FROM AUTHOR]

• Hierarchical structures are produced on steel using DLIP using multi-pulse exposure. • Moderate fluences and pulses produce patterns with envelopes over the reference level. • High laser fluence results in collapse of periodic structures and formation of craters. In this study, we report on the one-step fabrication of hierarchical microstructures on stainless steel substrates using multi-pulse Direct Laser Interference Patterning. The complex structures are produced using a two-beam interference setup with nanosecond laser pulses. The effect of laser fluence and number of pulses on the formation of multi-scale microstructures is systematically investigated. The resulting surface structures are characterized by scanning electron microscopy and white light interference microscopy. It was observed that at low laser fluence, the periodic microstructures remain defined and grow in height above the initial surface, independent on the number of pulses. For higher laser fluences as well as larger number of pulses, the structures adopt a crater-like morphology including a periodic line-like structure. [ABSTRACT FROM AUTHOR]