Picosecond Laser Texturing Research Articles

Wettability Behaviour of Metal Surfaces after Sequential Nanosecond and Picosecond Laser Texturing.

This study examines the wettability behaviour of 304 stainless steel (304SS) and Ti-6Al-4V (Ti64) surfaces after sequential nanosecond (ns) and picosecond (ps) laser texturing; in particular, how the multi-scale surface structures created influence the lifecycle of surface hydrophobicity. The effect of different post-process treatments is also examined. Surfaces were analysed using Scanning Electron Microscopy (SEM), a white light interferometer optical profiler, and Energy Dispersive X-ray (EDX) spectroscopy. Wettability was assessed through sessile drop contact angle (CA) measurements, conducted at regular intervals over periods of up to 12 months, while EDX scans monitored elemental chemical changes. The results show that sequential (ns + ps) laser processing produced multi-scale surface texture with laser-induced periodic surface structures (LIPSS). Compared to the ns laser case, the (ns + ps) laser processed surfaces transitioned more rapidly to a hydrophobic state and maintained this property for much longer, especially when the single post-process treatment was ultrasonic cleaning. Some interesting features in CA development over these extended timescales are revealed. For 304SS, hydrophobicity was reached in 1-2 days, with the CA then remaining in the range of 120 to 140° for up to 180 days; whereas the ns laser-processed surfaces took longer to reach hydrophobicity and only maintained the condition for up to 30 days. Similar results were found for the case of Ti64. The findings show that such multi-scale structured metal surfaces can offer relatively stable hydrophobic properties, the lifetime of which can be extended significantly through the appropriate selection of laser process parameters and post-process treatment. The addition of LIPSS appears to help extend the longevity of the hydrophobic property. In seeking to identify other factors influencing wettability, from our EDX results, we observed a significant and steady rate of increase in the carbon content at the surface over the study period.

Picosecond Laser Texturing of Al current collector to improve cycling performances and simplify recycling of Lithium-ion batteries

Lithium-ion batteries (LIBs) are one of the main energy storage technologies currently in use and recycling them offers significant economic, environmental, and material recovery benefits. Despite various recycling processes, separating the metallic current collector from the electrode composite film remains a crucial challenge. In this framework, the present study focuses on laser texturing of aluminum current collectors (CCs) to introduce a microscale surface architecture. The asymmetric surface pattern facilitated a controlled and directional adhesion, enhancing attachment to manage the significant volume variation of the active material (NMC811) during charging and discharging cycles. Additionally, it enabled an easy separation of the electrode composite layer from the current collector, during recycling, by applying a force in a specific direction. As a result, the laser-treated cathodes displayed low electrode polarization and increased cycling performances, with a capacity retention of 67.6 % after 300 cycles at 1C, thanks to the increased interfacial adhesion that reduced the active material delamination from the current collector upon cycling.

Attaining superhydrophobic and superoleophilic bronze surface by picosecond laser texturing and post-heat treatment

As a bearing material, bronze has high strength and hardness but is poor in anti-adhesion property. In this study, we propose a method to prepare a superhydrophobic and superoleophilic bronze surface by combining laser surface texturing and post-heat treatment. A picosecond laser was employed to produce pore arrays with varying spacings and depths on the bronze surface, which exhibited micro-nano hierarchical structures. A further post-heat treatment of the laser-textured sample at 150 °C in the ambient led to the formation of a superhydrophobic surface with a maximum water contact angle of 158° and with superoleophilicity. It was found that pore spacings played a significant role in forming the surface hierarchical structures, which were covered with the laser-ablated micro-nano particles. The pore depth, however, showed little influence on the surface wettability. Analysis of the surface chemical compositions by X-ray photoelectron spectroscopy (XPS) indicates that the C element mainly exists in the form of the C–C(H) group, which reduces the surface energy and leads to superhydrophobicity. It was also verified that the wettability transition of the bronze surface before and after heating was independent of the oxide transition. Rubbing tests were conducted to evaluate the durability of the surface hierarchical structure. Anti-icing and self-cleaning functions were demonstrated showing the potential of the developed method for preparing a superhydrophobic and superoleophilic surface.

Wetting Behavior Driven by Surface Morphology Changes Induced by Picosecond Laser Texturing.

The laser surface texturing (LST) technique has recently been used to enhance adhesion bond strength in various coating applications and to create structures with controlled hydrophobic or superhydrophobic surfaces. The texturing processing parameters can be adjusted to tune the surface's polarity, thereby controlling the ratio between the polar and dispersed components of the surface free energy and determining its hydrophobic character. The aim of this work is to systematically select appropriate laser and scan head parameters for high-quality surface topography of metal-based materials. A correlation between texturing parameters and wetting properties was made in view of several technological applications, i.e., for the proper growth of conformal layers onto laser-textured metal surfaces. Surface analyses, carried out by scanning electron microscopy and profilometry, reveal the presence of periodic microchannels decorated with laser-induced periodic surface structures (LIPSS) in the direction parallel to the microchannels. The water contact angle varies widely from about 20° to 100°, depending on the treated material (titanium, nickel, etc.). Nowadays, reducing the wettability transition time from hydrophilicity to hydrophobicity, while also changing environmental conditions, remains a challenge. Therefore, the characteristics of environmental dust and its influence on the properties of the picosecond laser-textured surface (e.g., chemical bonding of samples) have been studied while monitoring ambient conditions.

A dual-height wick to improve capillary performance of vapor chambers

The wick performance is a crucial metric for ensuring the reliable and efficient operation of vapor chambers (VCs) away from dry-out. To enhance the performance of VC, a pitcher plant inspired enhanced wick characteristic dual-height microgrooves (DHMW) was fabricated on 6063 aluminum alloy by one-step picosecond laser texturing without chemical modification. This study describes the two-step capillary behavior of DHMW by high-speed camera and infrared camera. The effects of minor rib number, groove height ratio, length scale, and test liquids (water, acetone, ethanol) on the capillary performance were investigated. When using water as the working fluid, the DHMW achieved a K/Reff of 1.182 µm, which was about 71.3 % larger than that of normal microgroove wicks due to the liquid propagation effect and the flow resistance reduction effect. Furthermore, the maximum K/Reff could reach 1.819 µm of the sample with a minor rib depth of about 70 μm. However, the wetting results showed that the droplets of acetone and ethanol tend to spread laterally after contact with the surface, which is unfavorable for the formation of hierarchical transport in the DHMW. This study demonstrates that laser texturing is an effective and controllable method for the complex shaping of grooved aluminum wicks, with the potential to improve the heat transport capability of VCs.

Picosecond laser-textured WC-10Co4Cr metal-ceramic composite coatings with high wear resistance property

The wear resistance properties of anilox roller have been a compelling challenge. A periodic array patterned WC-10Co4Cr metal-ceramic composite coatings is prepared by picosecond laser texturing. Coupled with the generation of cobalt oxide (CoO), tungsten oxide (WO3), di‑tungsten carbide (W2C), the laser processing mechanism is verified to involve the thermal vaporization of the metallic binder phase cobalt (Co), follow by the coulomb explosion removal of ceramic phase tungsten carbide (WC). The nano-hardness of the hexagonal (60°) mesh wall is maintained and even slightly increased by the synergy and competition among the formation of W2C, the removal of the metallic binder phase Co and the annealing softening of thermal effect. The prepared micro-structures on the surface which can capture debris and form stable lubricant film leads to a substantial reduction in both friction coefficient and wear rate, thereby resulting in remarkable improvements in wear resistance. In addition, the primary wear mechanism of the textured coating is found to be abrasive wear, accompanied by adhesive wear and oxidation wear. The integration of the metal-ceramic coatings and technology with laser processing enables the preparation of anilox roller with high hardness and exceptional wear resistance.

Superhydrophobic Fe-based amorphous alloy coatings with excellent anti-fouling and anti-corrosion properties by picosecond laser texturing

Producing superhydrophobic surfaces on the amorphous alloy coatings with excellent anti-corrosion and anti-fouling properties offers a promising strategy to broaden the applications of amorphous alloys in marine fields. In this work, the superhydrophobic surfaces on the Fe-based amorphous alloy coatings with micro-nano hierarchical structures were fabricated using picosecond pulsed laser texturing (LT) and surface chemical modification. The fabricated superhydrophobic coating surfaces have achieved a maximum contact angle of 166.5°and a minimum sliding angle of 3.6°. Additionally, these produced coatings also demonstrate outstanding self-cleaning and anti-fouling properties for preventing surface contamination. The superhydrophobicity originated from the formation of micro-nano hierarchical structures and the grafting of organic compounds with low surface free energy on the LT fabricated surfaces. The changes in wettability were attributed to the differences in the solid–liquid interfacial area fractions. The electrochemistry tests revealed that the corrosion resistance of the produced coatings with superhydrophobic surfaces had improved considerably compared with the as-sprayed amorphous alloy coatings, which could broaden the functional applications of the Fe-based amorphous alloy coatings.

Effect of picosecond laser texturing on the friction behavior of silicon carbide in hybrid ceramic bearings under dry and water lubrication

Hybrid ceramic bearings consisting of silicon carbide (SiC) and GCr15 steel have a wide range of applications. However, under unlubricated and water lubricated conditions, friction between SiC and GCr15 steel inevitably occurs due to interfacial contact (e.g. dry friction and boundary friction). Laser surface texturing, as a promising surface modification technique, has a significant impact on the material friction and wear characteristics aspects. In this paper, the UV picosecond laser was used to process a groove-textured structure on the surface of silicon carbide ceramics with the aim of comparatively investigating the effect of frictional properties of textured SiC surfaces and untextured SiC surfaces under dry friction and water lubrication conditions. The results showed that the picosecond laser successfully machined surface textures on the hard-to-process SiC surface, and the picosecond laser texturing had a significant effect on the tribological behavior of SiC ceramics. Under dry friction conditions, the coefficient of friction (COF) of picosecond laser-textured SiC with GCr15 steel increased (from 0.249 to 0.296) due to the micro-cutting effect and high surface roughness caused by the texture. In contrast, the COF of picosecond laser-textured SiC with GCr15 was significantly reduced under water-lubricated conditions (from 0.22 to 0.167), due to the facilitated frictional chemical reaction on the laser-textured surface, which favors the improved tribological properties of the silicon carbide friction interface.

Understanding the effects of picosecond laser texturing of silicon solar cells on optical and electrical properties

Understanding the effects of picosecond laser texturing of silicon solar cells on optical and electrical properties

Technological parameters optimization in picosecond laser texturing of titanium surfaces

The present paper deals with studying the surface morphology of commercially pure (cp) Ti Gr-2 and Ti6Al4V treated by a picosecond laser and with determining the optimal technological parameters for fabricating cavities with a regular shape and a depth of about 10 μm. The surfaces of disk-shaped samples were treated by a commercial picosecond laser with a power of 0.2 W, 0.5 W and 1 W and a number of pulses between 1,000 and 20,000. The samples’ surface was investigated by SEM and a non-contact 3D surface profiler. The technological parameters were optimized by regression analysis using the QStatLab software. It was found that after laser treatment with the lowest values of the above parameters only the surface roughness changed in the case of cp-Ti, while its Ti6Al4V counterpart had a “melted zone” with a 5.5-μm depth. Raising the values of the regime parameters mainly led to an increased cavity depth on the cp-Ti surface, while those on Ti6Al4V increased in all dimensions. The surface roughness of both materials was higher after the laser treatment and grew bigger as the laser power and the number of pulses were increased. The optimal technological parameters for treatment of cp-Ti and Ti6Al4V were found. The results obtained can be used for picosecond laser texturing of titanium surfaces using linear or dimple types of patterns.

Understanding the effects of picosecond laser texturing of silicon solar cells on optical and electrical properties

Understanding the effects of picosecond laser texturing of silicon solar cells on optical and electrical properties

Surface characteristics and wettability of superhydrophobic silanized inorganic glass coating surfaces textured with a picosecond laser

In this study, picosecond laser texturing was applied to enamel (an inorganic glass material) with micro-features that were then covalently absorbed with fluorosilane agents to produce superhydrophobic coatings. The resultant surfaces showed multiscaled structures of broccoli-like and cone-shaped pillars that resulted in excellent water-repelling properties with a water contact angle approaching 180°. The results proposed a surface area index to obtain the Cassie-Baxter hydrophobic state. The study also discussed the correlation of surface areal parameters to the Cassie-Baxter non-wetting state of the silanized samples. Most laser textured samples of ultrahigh water contact angles had similar surface metrological characteristics to natural leaves like alocasia odora and agave. The sample hierarchical surface structures had waviness constituents of platykurtic distribution, which were decorated with nano-submicron remelted enamel debris, which had leptokurtic distribution. The study has demonstrated the significant roles of surface metrology in the production of hierarchical morphologies to achieve the stable Cassie-Baxter superhydrophobicity.

Picosecond laser texturing on titanium alloy for biomedical implants in cell proliferation and vascularization.

Introducing specific textures to titanium alloy implant surface is helpful to modify the surface properties of materials. In this article, biomedical TC4 (Ti-6Al-4V) alloy was textured by a 10-ps infrared laser. Laser parameters that directly affected the detailed dimension of textures and its characteristics were optimized within laser power, defocusing amount, and scanning parameters via response surface methodology. These textures consisted of groove array about 30-90 μm in depth and 100 μm in width were prepared and their surface property (including surface morphology, element composition, wetting behavior, and biocompatibility) was analyzed. Surface characteristic analysis indicated that picosecond laser texturing improved surface properties and biocompatibility mainly by altering the microstructure and morphology of materials. In addition, laser textured groove array promoted contact area and hydrophobicity of material surface. Cell culture experiments and animal studies showed that titanium alloy implants with 30- and 60-μm-deep groove arrays on the surface-enhanced cell proliferation and adhesion. Meanwhile, compared to the polished samples, these groove arrays promoted the growth of new blood vessels and enhanced the combination of blood vessel and implants in vivo. That is, the deeper groove array was, and the better vascularizing effect the blood vessel exhibited.

Picosecond Laser-Textured Stainless Steel Superhydrophobic Surface with an Antibacterial Adhesion Property.

The pursuit of antibacterial properties on the surfaces of food container, medical equipment, and pharmaceutical tanks has been a compelling challenge for decades. Inspired by the biomimetic superhydrophobic surfaces that have self-cleaning, antifog, antisnow, and reduced bacterial adhesion properties, we use a simple and effective technology of a picosecond laser texturing for the fabrication of a superhydrophobic antibacterial surface on AISI 420 martensitic stainless steel plates. The laser-textured surface with micropapillae patterns with superimposed nanostructures exhibits outstanding in-air superhydrophobic and superaerophilicity underwater, which under the oscillation state resists an adhesion of 99% Escherichia coli and 93% Staphylococcus aureus and has hardly any bacterial adhesion under a stationary state. The comparative experiments verify that the robust air layer and hierarchical micro-nanostructures have come together to comprise the antibacterial mechanism. The laser-textured superhydrophobic surface also exhibits superior anticorrosion and antidestructive abilities with excellent antibacterial durability especially if deep cleaning is carried out after each dipping time in the bacterial suspension, promoting its leading-edge applications in medical, food, and pharmaceutical fields.

Tunable Bubble Assembling on a Hybrid Superhydrophobic-Superhydrophilic Surface Fabricated by Selective Laser Texturing.

Inspired by water striders walking on water, aluminum alloy plates with patterned superhydrophobic (SH) surfaces made by picosecond laser texturing and stearic acid treatment were enabled floating with load on water. Self-assembling of shape tunable air bubbles was achieved on the designated surface with hybrid SH/superhydrophilic (SHL) patterns that fabricated by the second selective laser texturing of the prepared SH plate. Different load-bearing capacities were obtained by changing the position and area of SH surfaces, and an outstanding weight loading capacity of 7.5 g on a 20 cm2 aluminum alloy plate (3750 g/m2, 1.34 times the self-weight) was gained with strip-shaped air bubbles adhered to the sample bottom surface. The drag reduction characteristics of SH/SHL surfaces with different shaped air bubbles were tested by a self-built single pendulum impact device; the results indicated that the sample with the whole exterior SH surface achieved the longest sailing distance, which is 26.7% increase than that of the untreated bare sample. The research implies a promising strategy to increase the load-bearing capacity and voyage of marine vehicles by manipulating the underwater solid/air/liquid interaction on biomimic functional surfaces.

Superhydrophobic and superhydrophilic functionalized surfaces by picosecond laser texturing

The study of laser textured surfaces has been carried out in the pursuit of superhydrophobic and superhydrophilic functional surfaces on stainless steel and silicon carbide substrate materials, respectively. The theoretical aspects of laser texturing a surface were investigated in order to understand how replication of micro- and nanoscale features could be achieved by high intensity picosecond pulsed laser systems. A series of laser parameters, pre-processing, and post-processing steps were developed to achieve contact angles of 152° as well as 0° on stainless steel and silicon carbide substrates, respectively. The substrates were used to demonstrate functional characteristics such as water repellency, self-cleaning, water adhesion, and dispersion of water using micro-capillary forces.

Picosecond laser micro/nano surface texturing of nickel for superhydrophobicity

A single step direct picosecond laser texturing process was demonstrated to be able to obtain a superhydrophobic surface on a nickel substrate, a key material for mold fabrication in the manufacture of various devices, including polymeric microfluidic devices. A two-scale hierarchical surface structure of regular 2D array micro-bumps with nano-ripples was produced on a nickel surface. The laser textured surface initially showed superhydrophilicity with almost complete wetting of the structured surface just after laser treatment, then quickly changed to nearly superhydrophobic with a water contact angle (WCA) of 140° in less than 1 d, and finally became superhydrophobic with a WCA of more than 150° and a contact angle hysteresis (CAH) of less than 5°. The mechanism involved in the process is discussed in terms of surface morphology and surface chemistry. The ultra-fast laser induced NiO catalytic effect was thought to play a key role in modifying the surface chemistry so as to lower the surface energy. The developed process has the potential to improve the performance of nickel mold in the fabrication of microfluidic devices.

Anti-biofouling superhydrophobic surface fabricated by picosecond laser texturing of stainless steel

Anti-biofouling technology is based on specifically designed materials and coatings. This is an enduring goal in the maritime industries, such as shipping, offshore oil exploration, and aquaculture. Recently, research of the relationship between wettability and antifouling effectiveness has attracted considerable attention, due to the anti-biofouling properties of the lotus leaf and shark skin. In this study, super-hydrophobic surfaces (SHSs) with controllable periodic structures were fabricated on AISI304 stainless steel by a picosecond laser, and their anti-biofouling performance were investigated by seawater immersion for five weeks in summertime. The results showed that the specimens with SHS demonstrate significant anti-biofouling effect as compared with the bare stainless steel plate. We observed that nearly 50% decrease of the average microbe attachment area ratio (Avg. MAAR) could be obtained. The micro-groove SHS with more abundant hierarchical micro-nano structures showed better anti-biofouling performance than the micro-pit SHS.

Investigating the effect of picosecond laser texturing on microstructure and biofunctionalization of titanium alloy

Laser processing technique has been an effective method to enhance the medical implant’s biocompatibility through forming specific textures on titanium alloy implant surface. In this paper, a 1064nm pulsed picosecond laser on TC4 titanium alloy implant samples was conducted to obtain optimal parameters for well-structured textures, controllable micro-grooves and improved osteoblast adhesion and proliferation. Picosecond laser technique is generally characterized by the high flexibility and advanced properties, which could make structural features including topography quality and detailed dimensions expediently improved and changed by adjusting laser processing parameters. To obtain the optimal laser processing parameters for desired microstructures, orthogonal experiments and related SEM, EDS and SPM analysis were conducted under various laser powers, repetition frequencies, scan speeds and scan numbers. Thus, the correlation between picosecond laser processing parameters and its corresponding microstructure feature of the micro-grooves was established. In addition, the immunofluorescence detection of cell actin cytoskeleton shows that structured textures can promote cell adhesion and play an important role in cell contact guidance.

Fabrication of broadband antireflective black metal surfaces with ultra-light-trapping structures by picosecond laser texturing and chemical fluorination

A hybrid method consisting of ultrafast laser-assisted texturing and chemical fluorination treatment was applied for efficiently enhancing the surface broadband antireflection to fabricate black titanium alloy surface with ultra-light-trapping micro-nanostructure. Based on the theoretical analysis of surface antireflective principle of micro-nanostructures and fluoride film, the ultra-light-trapping micro-nanostructures have been processed using a picosecond pulsed ultrafast laser on titanium alloy surfaces. Then fluorination treatment has been performed by using fluoroalkyl silane solution. According to X-ray diffraction phase analysis of the surface compositions and measurement of the surface reflectance using spectrophotometer, the broadband antireflective properties of titanium alloy surface with micro-nano structural characteristics were investigated before and after fluorination treatment. The results show that the surface morphology of micro-nanostructures processed by picosecond laser has significant effects on the antireflection of light waves to reduce the surface reflectance, which can be further reduced using chemical fluorination treatment. The high antireflection of over 98 % in a broad spectral range from ultraviolet to infrared on the surface of metal material has been achieved for the surface structures, and the broadband antireflective black metal surfaces with an extremely low reflectance of ultra-light-trapping structures have been obtained in the wavelength range from ultraviolet–visible to near-infrared, middle-wave infrared. The average reflectance of microgroove groups structured surface reaches as low as 2.43 % over a broad wavelength range from 200 to 2600 nm. It indicates that the hybrid method comprising of picosecond laser texturing and chemical fluorination can effectively induce the broadband antireflective black metal surface. This method has a potential application for fabricating antireflective surface used to improve the photothermal or photoelectric conversion efficiency of solar installations and enhancing the surface wave-absorbing capacity of devices.