Search Results (192)

We describe the formation of LIPSS by fs laser irradiation on polished titanium or steel samples, from which polymer replicas can be produced. The irradiation of inclined samples allows a variation in the periodicity of the LIPSS in a range between about 500 and 1000 nm, depending on the angle of incidence and the orientation of the laser polarization relative to the plane of incidence, either parallel (p-polarization) or perpendicular (s-polarization). For p-polarization, a second larger-size LIPSS feature with periodicities between about 1300 and 2200 nm is observed at medium angles. LIPSS lines are oriented perpendicular to the light polarization, except for s-polarization on steel samples, where a rotation of up to 35° is observed. In a two-step process, the LIPSS are replicated in polymers. We investigate the attachment of Schwann cells and fibroblasts seeded thereon, which show no direct dependence on the variation in the LIPSS periodicities. Full article

Soft-tissue management is critical for guided bone regeneration (GBR), yet conventional titanium meshes lack the ability to regionally regulate fibroblast behavior where opposite biological responses are needed. Here, we fabricated two femtosecond-laser patterned stripe topographies on titanium using a unidirectional scanning strategy with parameter tuning, generating LSFL with a periodicity of 820 ± 30 nm and micro-grooves with a periodicity of 4.7 ± 0.1 μm. Surface morphology and physicochemical properties were characterized by SEM/AFM, XPS, microhardness testing, and wettability measurements. Human gingival fibroblasts (HGF-1) were used to assess adhesion, cytoskeletal organization, spreading area, and proliferation (CCK-8). The submicron LSFL promoted robust fibroblast adhesion, aligned cytoskeletal organization, larger spreading areas, and higher proliferation, whereas the micro-groove surface markedly restricted spreading and was associated with poorer cytoskeletal organization and lower proliferation. Alternating patterned regions further demonstrated geometry-driven spatial selectivity, with preferential cell occupation on LSFL stripes. These findings support a fabrication-ready surface-engineering strategy to synchronize rapid soft-tissue sealing while restricting unwanted fibroblast advancement at defined regions, offering a promising route toward more predictable GBR outcomes. Full article

Laser surface texturing (LST) structures or laser-induced periodic surface structures (LIPSS) are typically created using laser pulses with durations ranging from femtoseconds to nanoseconds. However, nanosecond pulsed lasers, as cost-effective and more productive alternatives, can also be used to generate LST structures on stainless steel (SS) surfaces, making these structures more suitable for industrial applications. In this study, pulsed laser processing is employed to create LST structures on SS (AISI 304), with varying pulse and accumulated fluences, effective pulse counts, and scan parameters, such as pulse-to-pulse distance (pitch) and hatch spacing between scanning lines. A methodology for calculating oxidation density on processed AISI 304 surfaces is presented. Oxidation density, defined as the ratio of the oxidized area to the total processed area, is determined as a function of accumulated fluence, laser power, pulse-to-pulse distance, and hatch spacing. Optical images of the surfaces are analyzed, and oxidation regions are identified using machine learning techniques. The images are converted to grayscale, and machine learning algorithms are applied to classify the images into oxidation and non-oxidation regions based on pixel intensity values. This approach identifies the optimal threshold for separating the two regions by maximizing inter-class variance. Experimental modeling using response surface methodology is applied to experimentally generated data. Optimization algorithms are then employed to determine the process parameters that maximize pulsed laser irradiation performance while minimizing surface oxidation and processing time. This paper also presents a novel method for characterizing oxidation density using image segmentation and machine learning. The results provide a comprehensive understanding of the process and offer optimized models, contributing valuable insights for practical applications. Full article

High-entropy alloys (HEAs) represent one of the most promising emerging material families, particularly for advanced surface engineering applications. In this work, a near-high-entropy alloy (near-HEA) coating was produced on a 316L stainless steel substrate using laser metal deposition (LMD) from a powder mixture of Inconel 625, Cr and Mo, without the intentional addition of Fe. Due to dilution from the substrate, the resulting alloy contained elevated Fe content while maintaining Cr, Ni and Mo concentrations within the generally accepted compositional range of HEAs. The deposited layer exhibited a dual-phase microstructure consisting of a face-centered cubic (FCC) phase and a highly distorted tetragonal phase forming a periodic network with a characteristic length scale of several hundred nanometers. The hardness of the coating increased to approximately three times that of the substrate, reaching values of 600–700 HV. To further modify the surface properties, laser-induced periodic surface structures (LIPSS) were generated on the polished coating using femtosecond pulsed laser irradiation at different energy densities. The morphology and subsurface structure of the resulting periodic patterns were investigated by scanning electron microscopy. LIPSS with characteristic dimensions ranging from the micrometer to nanometer scale were successfully produced. Cross-sectional analyses revealed that the underlying dual-phase microstructure remained continuous within the laser-structured regions, indicating that LIPSS formation occurred predominantly via metallic ablation without significant phase transformation or amorphization. These results demonstrate the combined applicability of LMD and femtosecond laser structuring for producing mechanically enhanced, micro- and nanostructured near-HEA coatings with potential for advanced surface-related functionalities. Full article

In this work, we demonstrate precise control over laser-induced periodic surface structures (LIPSS) on stainless steel (SS) using femtosecond (fs) laser processing to suppress bacterial adhesion. We systematically compare the antifouling behavior of laser-textured surfaces with distinct pattern directionalities—linear and circular. Fs laser irradiation with linear polarization produces directional and anisotropic LIPSS, which progressively evolve into more complex hierarchical surface textures as processing conditions vary. In contrast, fs laser irradiation with circular polarization yields isotropic surface morphologies. Despite these morphological differences, the surface wettability remains nearly constant, with contact angles confined to a narrow range of 32.6–36.9°. Bacterial adhesion tests using Escherichia coli reveal that surfaces patterned with anisotropic features generated by linear polarization—particularly at an incident power of 30 mW—exhibit enhanced antifouling performance compared to isotropic counterparts. These results indicate that antifouling efficacy is governed not only by surface wettability but also by the spatial organization and anisotropy of the LIPSS. This study highlights the critical role of polarization-controlled fs laser processing in tailoring surface architectures and provides a rational strategy for designing bio-resistant metallic surfaces. Full article

Surface functionalisation of polymers is essential for enhancing properties such as wettability and mechanical resistance. This study presents a scalable, coating-free approach to fabricate hydrophobic and superhydrophobic Polydimethylsiloxane (PDMS) surfaces. Aluminium (AA2024) moulds were microstructured using a TruMicro femtosecond laser system to generate grid patterns with controlled hatch distances and depths, as well as laser-induced periodic surface structures (LIPSSs). These features were accurately replicated onto PDMS, as confirmed by scanning electron miscoscopy (SEM) and profilometry. Contact angle measurements showed a marked increase in hydrophobicity, reaching superhydrophobicity for optimised parameters, with surface stability maintained over four months without degradation. Full article

Today, the engineering of load-bearing bone tissue after severe trauma still relies on metal-based (Ti, CoCrMo alloys or stainless steel) permanent implants. Such artificial scaffolds are typically applied in the body and come into direct contact with the recipient’s cells, whose adhesion affects the patient’s implant acceptance or rejection. The present study aims to create a nano-rough texture by means of ultra-short femtosecond laser (fs)-induced periodicity in the form of laser induced periodic surface structures (LIPSS) on the surface of a stainless steel implant model, which is additionally functionalized via magnetron-sputtering with a thin Cu layer, thus providing the as-created implants with a stable antimicrobial interface. Calcium phosphate (CaP) crystal growth was additionally applied due to the strong bioactive interface bond that CaPs provide to the bone connective tissue, as well as for the strong interface bond they create between the artificial implant and the surrounding bone tissue, thereby stabilizing the implanted structure within the body. The bioactive properties in the as-created antimicrobial hybrid topographical design, achieved through femtosecond laser-induced nanoscale surface structuring and micro-sized CaP crystal growth, have the potential for subsequent practical applications in bone tissue engineering. Full article

In this study, we examine the characteristics of laser-induced periodic surface structures (LIPSSs) fabricated on N-doped 4H-SiC (N-SiC) and high-purity 4H-SiC (HP-SiC) crystals using femtosecond–picosecond lasers. The effects of various laser parameters on the orientation, size, and morphology of the LIPSS are systematically investigated. The results reveal that, under identical laser irradiation conditions, the area of LIPSS on both N-SiC and HP-SiC increases linearly with the number of pulses, with N-SiC exhibiting a higher growth coefficient. Furthermore, analysis of differences in photothermal weak absorption and electric field modulation during the LIPSS fabrication process indicates that distinct SiC crystals yield varied LIPSS formation outcomes. This work not only elucidates the underlying physical mechanisms governing LIPSS formation on different silicon carbide crystal surfaces but also provides valuable guidance for precisely controlling the size and orientation of LIPSS regions on various 4H-SiC substrates. Full article

With an aging population, the number of joint replacement surgeries is on the rise. One of the most common implant materials is cobalt–chromium–molybdenum (CoCrMo) alloy. Hence, the surface properties of this alloy have attracted increasing attention. In this study, nanosecond and femtosecond laser processing, followed by annealing, was employed to modify the CoCrMo surface. The effects of the treatment conditions on the surface morphology, structure, composition, hardness, roughness, contact angle, wear properties, and corrosion current were studied. Femtosecond laser processing with an energy density of 1273 mJ/cm², followed by heat treatment at 160 °C for 2 h, produced laser-induced periodic surface structures (LIPSS) without altering the chemical composition of the alloy and rendered the surface superhydrophobic. In contrast, nanosecond laser treatment at higher laser energy densities promoted the formation of an oxide layer, which improved the hardness and corrosion resistance of the substrate. Overall, the CoCrMo samples processed using the femtosecond laser system exhibited superior corrosion and wear resistance, with a protection efficiency of approximately 92%. Full article

Monitoring of laser-based processes is essential for ensuring the quality of produced surface structures and for maintaining the process stability and reproducibility. Optical methods based on scatterometry are attractive for industrial monitoring as they are fast, non-contact, non-destructive, and can resolve features down to the sub-microscale. Here, Laser-Induced Periodic Surface Structures (LIPSS) are produced on stainless steel using ultrashort laser pulses in combination with a polygon scanning system. After the process, the fabricated LIPSS features are characterized by microscopy methods and with an optical setup based on scatterometry. Images of the diffraction patterns are collected and the intensity distribution analyzed and compared to the microscopy results in order to estimate the LIPSS height, spatial period, and regularity. The resulting analysis allows us to study LIPSS formation development, even when its characteristic diffraction pattern gradually changes from a double-sickle shape to a diffuse cloud. The scatterometry setup could be used to infer LIPSS height up to 420 nm, with an estimated average error of 7.7% for the highest structures and 11.4% in the whole working range. Periods estimation presents an average error of ~5% in the range where LIPSS are well-defined. In addition, the opening angle of the LIPSS was monitored and compared with regularity measurements, indicating that angles exceeding a certain threshold correspond to surfaces where sub-structures dominate over LIPSS. Full article

Lithium–sulfur batteries (LSBs), possessing excellent theoretical capacities, advanced theoretical energy densities, low cost, and nontoxicity, are one of the most promising energy storage battery systems. However, some issues, including poor conductivity of elemental S, the “shuttle effect” of high-order lithium polysulfides (LiPSs), and sluggish reaction kinetics, hinder the commercialization of LSBs. To solve these problems, various carbon-based aerogels with developed surface morphology, tunable pores, and electrical conductivity have been examined for immobilizing sulfur, mitigating its volume variation and enhancing its electrochemical kinetics. In this paper, an extensive generalization about the effective preparation methods of carbon-based aerogels comprising the combined method of carbonization with the gelation of precursors and drying processes (ambient pressure drying, freeze-drying, and supercritical drying) is proposed. And we summarize various carbon carbon-based aerogels, mainly including graphene aerogels (Gas) and carbon nanofiber (CNF) and carbon nanotube (CNT) aerogels as cathodes, separators, and interlayers in LSBs. In addition, the mechanism of action of carbon-based aerogels in LSBs is described. Finally, we conclude with an outlook section to provide some insights into the application of carbon-based aerogels in electrochemical energy storage devices. Based on the discussion and proposed recommendations, we provide more approaches on nanomaterials in high-performance liquid or state LSBs with high electrochemical performance in the future. Full article

Laser-induced periodic surface structures (LIPSSs) produced via ultrafast laser-induced oxidation offer a promising route for high-quality nanostructuring, with reduced thermal damage compared to conventional ablation-based methods. However, the influence of laser repetition frequency on the formation and morphology of oxidized LIPSSs remains insufficiently explored. In this study, we systematically investigate the effects of varying the femtosecond laser repetition frequency from 1 kHz to 100 kHz while keeping the total pulse number constant on the oxidation-induced LIPSSs formed on amorphous silicon films. Scanning electron microscopy and Fourier analysis reveal a transition between two morphological regimes with increasing repetition frequency: at low frequencies, the long inter-pulse intervals result in irregular, disordered oxidation patterns; at high frequencies, closely spaced pulses promote the formation of highly ordered, periodic surface structures. Statistical measurements show that the laser-modified area decreases with frequency, while the LIPSS period remains relatively stable and the ridge width exhibits a peak at 10 kHz. Finite-difference time-domain (FDTD) and finite-element simulations suggest that the observed patterns result from a dynamic balance between light-field modulation and oxidation kinetics, rather than thermal accumulation. These findings advance the understanding of oxidation-driven LIPSS formation dynamics and provide guidance for optimizing femtosecond laser parameters for precise surface nanopatterning. Full article

Lithium–sulfur (Li-S) batteries are hindered by the sluggish electrochemical kinetics and poor reversibility of lithium polysulfides (LiPSs), which limits their practical energy density and cycle life. In order to address this issue, a novel Ni₃N/Nb₄N₅ heterostructure was synthesized via electrospinning and nitridation as a functional coating for polypropylene (PP) separators. Adsorption experiments were conducted in order to ascertain the heterostructure’s superior affinity for LiPSs, thereby effectively mitigating their shuttling. Studies of Li₂S nucleation demonstrated the catalytic role of the substance in accelerating the deposition kinetics of Li₂S. Consequently, Li-S cells that employed the Ni₃N/Nb₄N₅-modified separator were found to achieve significantly enhanced electrochemical performance, with the cells delivering an initial discharge capacity of 1294.4 mAh g⁻¹ at 0.2 C. The results demonstrate that, after 150 cycles, the cells retained a discharge capacity of 796.2 mAh g⁻¹, corresponding to a low capacity decay rate of only 0.25% per cycle. In addition, the rate capability of the cells was found to be improved in comparison to control cells with NiNb₂O₆-modified or pristine separators. Full article

Exploring advanced sulfur cathode materials is important for the development of lithium-sulfur batteries (LSBs), but they still present challenges. Herein, zinc oxide dots-modified vanadium nitride flower-like heterojunctions (Zn-QDs-VN) as sulfur hosts are prepared by a phase separation strategy. Characterizations confirm that the flower structure with high specific surface area and pores improves active site exposure and electron/mass transfer. In situ phase separation enriches the Zn-QDs-VN interface, addressing the issues of uneven distribution and interface reduction of Zn-QDs-VN. Further theoretical computations reveal that ZnO-QDs-VN with optimized intermediate spin states can constitute a stable LiS* bond sequence, which can conspicuously facilitate the adsorption and conversion of LiPSs and reduce the battery reaction energy barrier. Therefore, the ZnO-QDs-VN@S cathode shows a high initial specific capacity of 1109.6 mAh g⁻¹ at 1.0 C and long cycle stability (maintaining 984.2 mAh g⁻¹ after 500 cycles). Under high S loading (8.5 mg cm⁻²) and lean electrolyte conditions (E/S = 6.5 μL mg⁻¹), it also exhibits a high initial area capacity (10.26 mAh cm⁻²) at 0.2 C. The interfacial synergistic effect accelerates the adsorption and conversion of LiPSs and reduces the energy barriers in cell reactions. The study provides a new method for designing heterojunctions to achieve high-performance LSBs. Full article

The “shuttle effect” caused by the shuttling of soluble long-chain polysulfides between the anode and cathode electrodes has persistently hindered lithium–sulfur batteries (LSBs) from achieving stable and high-capacity performance. Numerous materials have been explored to mitigate the adverse effects of this phenomenon, among which metal oxides and metal sulfides are regarded as promising solutions due to their strong adsorption capability toward lithium polysulfides (LiPSs). However, the poor electrical conductivity of the metal oxides and sulfides, coupled with their inherent morphological limitations, makes it challenging to sustainably suppress LiPS shuttling. In this study, we designed a heterostructured catalyst composed of a metal oxide–metal sulfide heterostructure integrated with carbon nanotubes (CNTs). This design addresses the low conductivity issue of metal oxides/sulfides while optimizing the material’s morphology, enabling persistent LiPSs adsorption. Furthermore, the composite successfully facilitates three-dimensional (3D) Li₂S deposition. The assembled battery exhibits stable and high-capacity performance, delivering an initial discharge capacity of 622.45 mAh g⁻¹ at 2C and retaining 569.5 mAh g⁻¹ after 350 cycles, demonstrating exceptional cycling stability. Full article