Laser Surface Structuring Research Articles

Biocompatibility and drug release kinetics of TiNbZrSn femtosecond laser-induced superhydrophilic structures

As load-bearing components, metallic implants are frequently used for orthopedic prostheses due to their superiority over conventional ceramic and polymeric biomaterials. Metal-based orthopedic implants have been subjected to various fabrication and treatment methods to enhance their biological activities at the host site. Modifying the structure, improving the hydrophilicity, and developing controlled-release drug delivery systems can improve cellular adhesion, proliferation, osseointegration, and differentiation. Ultrafast lasers have recently attracted interest in surface engineering. Laser surface structuring permits the alteration of sample topography, the chemical makeup of the surface, and the material physical properties. This study presents the surface modification of a TiNbZrSn shape memory alloy using a femtosecond laser to produce laser-induced periodic structures with better drug release than that of a pristine sample. We also present the in vitro cell viability and biocompatibility of the alloy system. All samples structured with femtosecond laser exhibited superhydrophilic nature with 0° contact angle. In addition, the laser structured surfaces showed cell viability above 80 % and minimal cytotoxicity towards human keratinocytes. Moreover, a well-defined hydroxyapatite layer developed on the laser structured surface. In general, the laser structuring process and the induced changes on the surface in terms of roughness and oxide formation result in slower drug release (up to 10 %) compared to pristine specimens.

Influence of nanoparticulates and microgrooves on the secondary electron yield and electrical resistance of laser-treated copper surfaces

Laser surface structuring has proven to be an effective technique for achieving a copper surface with secondary electron yield (SEY) values close to or below unity. However, the attributes that minimize SEY, such as moderately deep grooves and redeposited nanoparticles, may lead to undesirable consequences, including increased radio frequency surface resistance. This investigation systematically examined data about different cleaning procedures designed to eliminate redeposited adsorbed particulates. Various analysis techniques were used iteratively after each consecutive cleaning step, providing insights into the evolving surface characteristics. The collected experimental results identified distinct impacts of microgrooves, groove orientation, and associated particulates on secondary electron yield and surface resistance. Exposing the crests while retaining high particulate coverage in the grooves leads to reduced SEY values and surface resistance, suggesting that the tips of the grooves exert a more significant influence on surface current density than the groove depth. At the same time, nanoparticles in the grooves have a more significant impact on SEY values than the exposed tips at the surface. Published by the American Physical Society 2024

Advanced Laser Techniques for the Development of Nature-Inspired Biomimetic Surfaces Applied in the Medical Field

This review focuses on the innovative use of laser techniques in developing and functionalizing biomimetic surfaces, emphasizing their potential applications in the medical and biological fields. Drawing inspiration from the remarkable properties of various natural systems, such as the water-repellent lotus leaf, the adhesive gecko foot, the strong yet lightweight spider silk, and the unique optical structures of insect wings, we explore the potential for replicating these features through advanced laser surface modifications. Depending on the nature and architecture of the surface, particular techniques have been designed and developed. We present an in-depth analysis of various methodologies, including laser ablation/evaporation techniques, such as Pulsed Laser Deposition and Matrix-Assisted Pulsed Laser Evaporation, and approaches for laser surface structuring, including two-photon lithography, direct laser interference patterning, laser-induced periodic surface structures, direct laser writing, laser-induced forward transfer, and femtosecond laser ablation of metals in organic solvents. Additionally, specific applications are highlighted with the aim of synthesizing this knowledge and outlining future directions for research that further explore the intersection of laser techniques and biomimetic surfaces, paving the way for advancements in biomedical applications.

Near-Field-Regulated Ultrafast Laser Supra-Wavelength Structuring Directly on Ultrahard Metallic Glasses.

The ultrafast-laser-matter interactions enable "top-down" laser surface structuring, especially for materials difficult to process, with "bottom-up" self-organizing features. The subwavelength scenarios of laser-induced structuring are improved in defects and long-range order by applying positive/negative feedbacks. It is still hardly reported for supra-wavelength laser structuring more associated with complicated thermo/hydro-dynamics. For the first time to the knowledge, the near-field-regulated ultrafast-laser lithography of self-arrayed supra-wavelength micro/nano-pores directly on ultra-hard metallic glass is developed here. The plasmonic hot spots on pre-structures, as the positive feedback, clamped the lateral geometries (i.e., position, size). Simultaneously, it drilled and self-organized into micro/nano-pore arrays by photo-dynamic plasma ablation and Marangoni removal confined under specific femtosecond-laser irradiation, as the negative feedback. The mechanisms and finite element modeling of the multi-physical transduction (based on the two-temperature model), the far-field/near-field coupling, and the polarization dependence during laser-matter interactions are studied. Large-area micro/nano-pore arrays (centimeter scale or larger) aremanufactured with tunable periods (1-5µm) and geometries (e.g., diameters of 500 nm-6µm using 343, 515, and 1030 lasers, respectively). Consequently, the mid/far-infrared reflectivity at 2.5-6.5µm iss decreased from ≈80% to ≈5%. The universality of multi-physical coupling and near-field enhancements makes this approach widely applicable, or even irreplaceable, in various applications.

Femtosecond laser processing of amorphous silicon films

Femtosecond laser micromachining is a pivotal approach within the dynamic field of laser surface structuring, offering unparalleled precision for materials processing. By exploiting the unique nonlinear light-matter interactions, this technique allows the creation of functional micro- and nanostructures with exceptional accuracy and reproducibility. Of particular interest is its ability to process diverse materials, including glasses, polymers, metals, and semiconductors, with minimal thermal impact and collateral damage. Moreover, femtosecond laser micromachining eliminates the need for traditional lithographic methods, enabling intricate structure fabrication under ambient conditions, thereby revolutionizing microfabrication techniques. This study demonstrates the micromachining using femtosecond lasers at 800 nm wavelength and explores the critical role of process parameters, such as laser pulse energy and the number of pulses in determining the damage threshold fluence, especially considering incubation effects in multi-pulse scenarios. Furthermore, it explores the potential of femtosecond laser micromachining for controlled crystallization in hydrogenated amorphous silicon (a-Si:H), unleashing enhanced electrical and optical properties. With its versatility, precision, and potential for diverse applications, femtosecond laser micromachining holds promise for driving advancements in electronic and photonic devices, particularly in high-efficiency photovoltaics, integrated photonics, and novel optoelectronic technologies.

Laser surface structuring of diamond-like carbon films for tribology

The paper overviews experimental findings of the direct laser processing and surface microstructuring (texturing) of various diamond-like carbon films (a-C:H, ta-C, DLN, metal-doped DLN), aimed at improvements of their tribological and nanotribological properties. The nanosecond UV and femtosecond IR/visible pulsed lasers were applied in microprocessing of the films, focusing on high precision surface structuring with fs-laser pulses. The studies were concentrated on the following tasks: (i) surface graphitization in laser microstructuring of the films under different irradiation conditions, (ii) lubricated friction performance of DLN films micropatterned with UV ns and visible fs pulsed lasers, and (iii) nanoscale friction of laser-structured DLN and metal-doped DLN films examined with contact-mode atomic force microscopy. The important findings of our studies are related to fabrication of highly-precise microgroove/microcrater patterns on DLN films and improvements of frictional properties of the laser-structured films at the macro, micro and nanoscale. The surface microstructures improved the film properties under oil-lubricated sliding in dependence on their geometrical parameters (size, depth, period) and ambient temperature. The nanoscale friction behavior of laser-structured films was shown to be controlled by the surface graphitization, nanoscale roughness, capillary forces and wear of AFM tips during friction force imaging.

Laser surface structuring of titanium alloy (Ti-6Al-4V) for improved tribocorrosion resistance for bio-implant applications

In this study, laser surface structuring (LSS) of titanium alloy (Ti-6Al-4 V) using pulsed Nd: YLF laser with 100 ns pulse duration at various laser powers, scan speeds, and line-spacings has been undertaken for improving the tribocorrosion property. Due to LSS, there is an increment in nano hardness (4.9 GPa - 6.3 GPa) and Young's modulus (140 GPa − 153 GPa) when compared to untreated Ti-6Al-4 V (3.9 GPa, 123 GPa). The tribocorrosion behavior in simulated body fluid against the ZrO2 ball in fretting mode shows that due to LSS, the degradation rate was significantly reduced (5.3–67.2%) when compared to the untreated one. With an increase in load, the coefficient of friction and material removal rate increases. The mechanism of tribocorrosion is established.

Effect of process parameters on the corrosion kinetics and mechanism of nanosecond laser surface structured titanium alloy (Ti6Al4V)

In this study, laser surface structuring (LSS) of Ti6Al4V was carried out using an Nd:YLF laser with a second harmonic wavelength of 527 nm and a pulse duration of 100 ns at varied laser fluence, scan speed, and line spacing. A detailed study of the effect of process parameters on surface topography, microstructure, composition, phase, contact angle, electrochemical behavior, and bioactivity was undertaken. Nanosecond pulsed laser irradiation with overlapping resulted in the formation of linear continuous grooves on the surface due to ablation/evaporation of materials. There is the formation of oxides of titanium (TiO2 and Ti2O3) whose mass fractions varied with process parameters. The average microhardness of the laser-structured region was improved (393 VHN - 535 VHN) as compared to the as-received Ti6Al4V (303 VHN). The contact angle of simulated body fluid (SBF) against the structured surface (58°- 123°) showed increased contact angle as compared to as-received samples (50°). The laser surface structuring exhibited a superior corrosion resistance property (in SBF) as compared to as-received Ti6Al4V. The mechanism of corrosion behavior was established by electrochemical impedance spectroscopic study (in SBF). The optimum process parameter for the LSS of Ti6Al4V with enhanced hardness and corrosion resistance was derived. The LSS surface processed under the optimum parameters measured by immersing in SBF revealed a higher deposition of calcium phosphate as compared to the as-received Ti6Al4V.

High‐Speed Laser Surface Structuring for Thermal Spray Coating Preparation

The preparation of surfaces for coating processes is indispensable for maximal adhesion and good coating results. These technical surfaces can be treated by chemical, mechanical, or physical procedures. In thermal spray coating, grit blasting is a standard process for surface preparation. This mechanical roughening and activation of the surfaces is fast and easy to handle. On the negative side, the grit gets wasted and the generated pattern is inflexible. Therefore, attempts to substitute grit blasting with a laser application is discussed in this article. Herein, a theoretical evaluation of high‐speed laser surface texturing (LST) is performed to find limits and points for the optimization of these processes. To estimate the surface processing rates, continuous wave, nanosecond, and ultrashort pulse laser machined dimples and grooves are investigated, and results of the spray coatings are presented afterward. The steel substrates are coated with Stellite 6 and tungsten. Adhesion tests and coating structures are analyzed. In terms of the optimization of the laser texturing, in situ temperature measurements show the influence of the laser process speed on the thermal load of the substrate. The influence of the number of scanning repetitions on heat accumulation during LST is also analyzed.

Femtosecond laser induced damage threshold incubation and oxidation in AS2S3 and AS2Se3 thin films

Laser surface structuring has emerged as a versatile technology for precise and localized material processing. When dealing with femtosecond lasers, thermal effects and collateral damage are reduced due to nonlinear light-matter interaction, improving the processing. This study explores the fabrication of microstructures using femtosecond pulses on thin films of chalcogenide glasses, which can be used for photonics applications, such as waveguides, fiber lasers, and photonic crystals. Moreover, the photoinduced changes in chalcogenide glasses have opened up new possibilities in optoelectronics, data storage, and other applications. Femtosecond laser machining of amorphous thin films of As2S3 and As2Se3 using femtosecond laser pulses is investigated through various microscopy techniques and spectroscopy tools, focusing on the impact of incubation effects and controlled photo-oxidation. This research contributes to a deeper understanding of the interaction of ultrafast pulses with chalcogenide glasses, promoting further advancements in photonics and optoelectronic applications.

Chemical and mechanochemical degradations of ultrafast laser surface structured Ti6Al4V in simulated body fluid environment

In the present study, the effect of ultrafast laser surface structuring of Ti6Al4V (using a Ti: Sapphire laser with a pulse duration of 100 fs and 3000 fs) on its surface topography, nanomechanical properties, tribocorrosion property, and bioactivity has been undertaken. Surface structuring leads to defect-free periodic surface structures with shockwave-induced compressive residual stresses and grain refinement (subgrain size of 5.2 µm) as compared to as received Ti6Al4V (26 µm). There is a significant enhancement in nano hardness (5600–5800 MPa) and Young's modulus (139 – 148 GPa) as compared to as received Ti6Al4V ((nano hardness of 3800 MPa), (Young's modulus of 117 GPa)) due to laser surface structuring. The tribocorrosion kinetics were significantly reduced in laser surface structured Ti6Al4V as compared to as received one. The individual influence of tribocorrosion property was established. A detailed microstructural study and immersion studies showed the presence of a higher fraction of calcium phosphate deposition in surface-structured samples (0.0432–0.0461 mg/cm2 after 7 days) as compared to as received Ti6Al4V (0.018 mg/cm2 after 7 days). The presence of hydroxyapatite has been confirmed by X-ray photoelectron spectroscopic analysis.

Localized in-situ deposition: a new dimension to control in fabricating surface micro/nano structures via ultrafast laser ablation

Controllable fabrication of surface micro/nano structures is the key to realizing surface functionalization for various applications. As a versatile approach, ultrafast laser ablation has been widely studied for surface micro/nano structuring. Increasing research efforts in this field have been devoted to gaining more control over the fabrication processes to meet the increasing need for creation of complex structures. In this paper, we focus on the in-situ deposition process following the plasma formation under ultrafast laser ablation. From an overview perspective, we firstly summarize the different roles that plasma plumes, from pulsed laser ablation of solids, play in different laser processing approaches. Then, the distinctive in-situ deposition process within surface micro/nano structuring is highlighted. Our experimental work demonstrated that the in-situ deposition during ultrafast laser surface structuring can be controlled as a localized micro-additive process to pile up secondary ordered structures, through which a unique kind of hierarchical structure with fort-like bodies sitting on top of micro cone arrays were fabricated as a showcase. The revealed laser-matter interaction mechanism can be inspiring for the development of new ultrafast laser fabrication approaches, adding a new dimension and more flexibility in controlling the fabrication of functional surface micro/nano structures.Graphical

Generation of periodic nanobumps through a double-scan method with femtosecond lasers

Ultrafast laser surface structuring is a promising technique for precisely controlling the surface functions of materials. Nanoripples, the typical laser-induced periodic surface structures, are effective at regulating surface colors, but only in one view direction. To overcome this issue, effective methods for fabricating other types of structures are needed. In this study, we successfully form periodic nanobump structures using a simple double-scan approach, in which the same surface is subjected to two consecutive laser scans with different polarization directions. The formation behavior of these intriguing nanostructures is investigated in relation to laser parameters such as peak laser fluence, overlapping ratio, and polarization angle between two scans. The formation mechanism is hypothesized and confirmed. The obtained nanobumps exhibit exceptional optical performance compared to nanoripples by enhancing the visibility angle, hence expanding the possible applications of the ultrafast laser surface structuring technique.

Periodic Surface Structuring of Copper with Spherical and Cylindrical Lenses

The use of a cylindrical lens in femtosecond laser surface structuring is receiving attention to improve the processing efficiency. Here, we investigate the structures produced on a copper target, in air, by exploiting both spherical and cylindrical lenses for beam focusing, aiming at elucidating similarities and differences of the two approaches. The morphological features of the surface structures generated by ≈180 fs laser pulses at 1030 nm over areas of 8 × 8 mm2 were analyzed. For the spherical lens, micron-sized parallel channels are formed on the target surface, which is covered by subwavelength ripples and nanoparticles. Instead, the cylindrical lens leads to a surface decorated with ripples and nanoparticles with a negligible presence of micro-channels. Moreover, the morphological features achieved by focusing ≈180 fs laser pulses at 515 nm with the cylindrical lens and varying the scanning parameters were also studied. The experimental results evidence a direct effect of the hatch distance used in the scanning process on the target surface that contains dark and bright bands corresponding to regions where the rippled surface contains a richer decoration or a negligible redeposition of nanoparticles. Our findings can be of interest in large area surface structuring for the selection of the more appropriate focusing configuration according to the final application of the structured surface.

Generation of terahertz vector beam bearing tailored topological charge

Optical vector beams have great potential in many applications, for example optical tweezers, information transmission and processing, laser surface structuring, particle acceleration, and vortex dichroism spectroscopy. However, the reported vector beams in the terahertz (THz) spectral range are limited to exhibiting only low-order topological charges. Therefore, methodologies to generate THz vector beams bearing a tailored topological charge are highly desired. This work investigates how to generate THz vector beams with a tailored topological charge via the optical rectification process in a 111-cut ZnTe crystal pumped with a vector optical beam and how to manipulate the vector THz beam’s polarization state through the initial polarization angle. We theoretically and experimentally demonstrate that the transduction process produces a THz topological charge twice that of the infrared pump, also admitting the opposite sign. Given the well-developed technology to design infrared vector beams, the proposed method can generate THz vector beams with tailored topological charges.

Femtosecond laser structuring in the fabrication of periodic nanostructure on titanium for enhanced photoelectrochemical dopamine sensing performance

Femtosecond laser structuring in the fabrication of periodic nanostructure on titanium for enhanced photoelectrochemical dopamine sensing performance was reported. The formation of laser induced periodic surface structures (LIPSS) upon titanium foil depended on the polarization of the femtosecond laser beam. When linearly and radially polarized femtosecond laser beam interacted with titanium foil, LIPSS were generated on titanium surface and further used for the fabrication of electrode material in photoelectrochemical dopamine sensing. Field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), and UV–vis absorption spectra were performed to study the surface characteristics of the laser treated titanium foil. The results revealed that low spatial frequency LIPSS (LSFL) formation occurred at both cases of the linearly and radially polarized laser treated titanium foil with a period of about 350 and 250 nm and owned the significant surface chemical and structural modification (abundant Ti4+ state and hydroxyl functional group), especially in term of radially polarized laser treated titanium foil. The radially polarized laser treated titanium foil owning optimal surface structural modification contributed multiple catalytically active sites and made the outstanding photoelectrochemical performance of dopamine sensing. It was concluded that femtosecond laser surface structuring made it possible to modify the surface characteristics of objects for future construction of sensing platforms.

Effect of scanning speed on molten metal behaviour under angled irradiation with a continuous-wave laser

Laser processing is one of the most suitable technologies for fabricating controlled structures consisting of grooves or holes having a depth of several tens of micrometres on a metal surface. These structures are expected to improve the characteristics of the surface, such as its adhesiveness to metal and plastics. To control the surface structures, it is important to understand the dynamic behaviours during laser processing. Surface processing using an angled continuous-wave (CW) laser irradiation has been proposed for high-speed surface structuring. Distinct structures consisting of high upheavals on the incident side of the irradiated laser beam and wide grooves on the reflection side are formed on metal surfaces using this proposed method. The dynamic phenomena of molten metal during laser irradiation were investigated by examining the effect of scanning speed via experiments and thermal fluid analyses under the conditions of an average power of 200 W, an irradiation angle of 60°, and a scanning speed of 0.5–2.0 m/s. High-speed camera observations and fluid analysis revealed that the molten metal flow velocity from the reflection side to incident side significantly increased with an increase in scanning speed. Thus, the molten metal was dispersed on the reflection side and accumulated on the incident side. These asymmetric molten metal behaviours resulted in the formation of distinct surface structures. The detailed analyses of molten metal behaviours conducted in this study will help clarify the phenomena associated with high-speed laser surface structuring.

Femtosecond laser surface structuring of silicon in dynamic irradiation conditions

The process of surface structuring of silicon in dynamic irradiation conditions is investigated by analyzing the features of the surface structures generated on a target moving at different scanning velocities under the irradiation by a 1030 nm femtosecond laser beam. Scanning electron microscopy analysis of the shallow linear craters produced in different experimental conditions allows characterizing the dependence of threshold fluence for the formation of surface structures (ripples and grooves) as well as their spatial periods on the effective number of laser pulses. Moreover, the effect of the accumulated laser fluence dose has been also addressed. Our findings evidence clear trends of the morphological features of the surface structure on the effective number of laser pulses as well as the existence of interesting differences in their characteristics when processing occurs at the same value of the accumulated laser fluence dose achieved by appropriate selection of laser pulse energy and scanning speed.

Investigation on the mechanism of a new laser surface structuring by laser remelting

A new method of surface structuring by laser remelting with the help of surface tension (mainly thermocapillary force and solutocapillary force) and volume expansion was proposed. A multiphysics coupled numerical model was proposed for this surface structuring method, in which the calculation of surface tension and solutocapillary force is improved. Using the established numerical model, the formation mechanism of the surface structure was explored from the aspects of surface tension, fluid flow, volume expansion, and surface profile evolution. The reason why the surface structure changes from a “W” shape to an “A” shape was explained, and the contributions of thermocapillary force, solutocapillary force, and volume expansion to the surface structure were investigated. The effects of laser power, scanning speed, and beam diameter on the surface profile of the surface structure were studied by experiments, which indicates that the desired surface structure can be obtained by adjusting the process parameters. All the experimental results were simulated by the established numerical model, and the simulation results are in good agreement with the experimental results, indicating that the numerical model is effective and available.

Effect of Laser Surface Structuring on Surface Wettability and Tribological Performance of Bulk Metallic Glass

Bulk metallic glasses (BMGs) have been extremely popular in recent decades, owing to their superior properties. However, how to improve the surface functions and durability of BMGs has always been a key engineering issue. In this work, a facile laser-based surface structuring technique was developed for modulation and control of the surface functionalities of Zr-based BMG. For this technique, a laser beam was first irradiated on the surface to create periodic surface structure, followed by heat treatment to control surface chemistry. Through experimental analyses, it was clearly shown that laser surface structuring turned the BMG surface superhydrophilic, and subsequent heat treatment turned the surface superhydrophobic. We confirmed that the combination of laser-induced periodic surface structure and modified surface chemistry contributed to the wettability transition. The laser-heat-treated surface also exhibited improved antifriction performance with the help of lubrication medium. This work provides a feasible method for surface modification of BMG, suggesting applications in the areas of medicine, biology and microelectronics.