Femtosecond Laser Structuring Research Articles

The influence of ultrafast laser processing on morphology and optical properties of Au-GaAs composite structure

The results of direct femtosecond laser structuring of GaAs wafer coated with continuous semitransparent gold (Au) film are presented. The obtained structures demonstrate a combination of different features, namely laser-induced periodic surface structures (LIPSS) on semiconductor and metal film, nanoparticles, Au islands, and fragments of exfoliated Au film. The properties of Au-GaAs samples are studied with scanning electron microscopy (SEM), Raman scattering, and photoluminescence (PL) spectroscopy. The behaviour of phonon modes and enhancement of band-edge PL of Au-GaAs composite sample are discussed. The Raman spectra of Au-GaAs sample processed at different levels of irradiation pulse energy reveal forbidden TO and allowed LO phonon modes for selected geometry of experiment, as well as the manifestation of GaAs surface oxidation and amorphization. A 12-fold increase of PL intensity for Au-GaAs sample with LIPSS compared to initial GaAs surface is observed. The detected PL enhancement is caused by an increase of absorption in GaAs due to the light field enhancement near the Au nanoislands and a decrease of nonradiative surface recombination. The blue shift of PL band is caused by the quantum size effect in GaAs nano-sized features at laser processed surface. The combination of GaAs substrate with surface micro- and nanostructures with Au nanoparticles can be useful for photovoltaic and sensorics applications.

Templated silver nanoparticle deposition on laser-induced periodic surface structures for SERS sensing

Organized assemblies of metal nanoparticles exhibit unique optical properties and can be used as platforms for surface-enhanced Raman scattering (SERS) to detect small amounts of analyte molecules. In this work, we demonstrate that using Yb:KGW femtosecond laser structuring of silicon wafer we can modify surface properties by creating laser-induced quasi periodic surface structures (LIPSS) of 850 ± 43 nm periodicity. We show that silicon with LIPSS is a suitable surface for direct nanoparticle deposition because of its superhydrophilic properties and the nanoparticle density affects the density of the hot spots contributing in the Raman enhancement. We have analyzed the influence of the silver nanoparticle deposition on the structured silicon surface conditions on their density and coverage. 101±8 nm size silver nanoparticles were deposited by two methods, namely drop casting colloidal solution at three different temperatures (4 °C, 21 °C, 35 °C) and their SERS enhancements were compared with the monolayers deposited by liquid-liquid interface. It was found that monolayer deposition on a structured surface was the best approach in the sense of even silver nanoparticles coverage which exhibited best SERS performance reaching a limit of detection of 10−7 M for 2-naphthalenethiol. The obtained LoD is comparable with that of commercial substrates available in the market.

Icing Wind Tunnel and Erosion Field Tests of Superhydrophobic Surfaces Caused by Femtosecond Laser Processing

Ice accumulation on lift-generating surfaces, such as rotor blades or wings, degrades aerodynamic performance and increases various risks. Active measures to counteract surface icing are energy-consuming and should be replaced by passive anti-icing surfaces. Two major categories of surface treatments—coating and structuring—already show promising results in the laboratory, but none fulfill the current industry requirements for performance and durability. In this paper, we show how femtosecond laser structuring of stainless steel (1.4301) combined with a hydrocarbon surface treatment or a vacuum treatment leads to superhydrophobic properties. The anti-ice performance was investigated in an icing wind tunnel under glaze ice conditions. Therefore, flexible steel foils were laser-structured, wettability treated and attached to NACA 0012 air foil sections. In the icing wind tunnel, hydrocarbon treated surfaces showed a 50 s ice build-up delay on the leading edge as well as a smoother ice surface compared to the reference. To demonstrate the erosion resistance of these surfaces, long-term field tests on a small-scale wind turbine were performed under alpine operating conditions. The results showed only minor erosion wear of micro- and nano-structures after a period of six winter months.

Hydrophilic properties of the aluminum alloy induced by femtosecond laser structuring

This study explored the changes in wetting property and surface morphology in aluminum alloy plates due to femtosecond laser structuring. The laser scanning produced a hierarchical micro- and nano-scale structure consisting of microchannels decorated by irregular shape particles. The surface morphology was controlled by laser power and scanning line density. The surface wettability gradually changed from hydrophilic to hydrophobic one due to various chemical reactions for low laser power and scanning line density. However, femtosecond laser structuring with appropriate laser power and scanning line density was demonstrated to maintain strong and stable hydrophilic properties of aluminum alloy surfaces.

Generating colours through a novel approach based on spatial ALD and laser processing

This work studies the combination of direct femtosecond laser structuring of metal surfaces and Spatial Atomic Layer Deposition (SALD) of metal oxides as a novel approach to generate colours on different types of day-to-day metallic objects. In particular, a stainless-steel knife and an outdated 25 ct Dutch florin coin have been selected for the study. Our results show that it is possible both, to preserve the iridescence properties produced by laser processing and to tune the final metal surface colour by controlling the thickness of the ZnO coating. At the same time, this oxide coating could act as a protecting layer for the original material. We thus explore two different strategies to generate colour, namely, iridescence and interference, which can be even developed selectively. This novel methodology to colour metallic surfaces is a promising route to achieve cheap, scalable, and high-throughput processing methods and opens up a new avenue of possibilities and applications related to colour.

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.

Oxygen evolution reaction enhancement of copper electrodes in alkaline medium using ultrafast femtosecond laser structuring

In the pursuit of enhancing the oxygen evolution reaction (OER) activity, we employed femtosecond (FS) laser-induced surface nano-structuring to extend the surface area of copper (Cu) electrodes. Compelling surface hierarchical microstructures have been generated on the electrode surface using this approach. By optimizing the laser processing parameters, regular arrays of conical microstructures are fully covered by a thick and porous layer of Cu2O. Electrochemical measurements reveal that FS laser structuring developed large and structure-tunable surface areas with relative roughness factor between 51 and 61. The enhanced surface area and FS laser-induced Cu2O layers significantly enhanced the OER activity leading to a reduced overpotential (η10 = 345 mV) that is 70% less than that of pristine Cu at a current density of 10 mA cm−2. The results demonstrate the effectiveness of femtosecond laser-based surface structuring in enhancing the electrocatalytic OER activity of Cu electrodes in alkaline media.

Enhancement of the corrosion resistance of mild steel with femtosecond laser- nanostructuring and CrCoNi medium entropy alloy coating

In this work, the corrosion resistance of mild steel surface nanostructured with a femtosecond laser and coated with high corrosion resistant CrCoNi (CCN) medium entropy alloy through magnetron sputtering is studied. Substantial improvement in corrosion protection was achieved by applying a combination of high-power femtosecond laser surface nano-structuring at ambient conditions and thin-film coating with (CCN) medium entropy alloy. XRD analysis revealed that femtosecond laser structuring increases the susceptibility of the surfaces to Fe2O3 nucleation through oxidation. The surface wettability measurements and electrochemical polarization tests revealed that the combined approach of femtosecond laser structuring and magnetron sputter coating is the best for desired high corrosion resistance. Through this novel method, the resulting corrosion resistance of mild steel was improved by more than one-fold. The results are explained considering the detailed microstructural analysis. The presented findings open new possibilities for corrosion prevention using a combination of new powerful technologies that yield to unprecedented corrosion-inhibition efficacy.

Single-Step femtosecond laser structuring of multifunctional colorful metal surface and its origin

Metal colorizing by ultrafast laser has aroused great attention in the fields of industrial marking and anti-counterfeiting. However, its colorizing mechanism is still not very clear and lurks beneath its beautiful exterior. In the present work, pure copper is used as a case study object for metal colorizing. The copper surface treated by femtosecond laser direct writing (fs-LDW) is endowed with black, bluish-violet, and iridescent color under different illumination and observation conditions. An in-depth study of the mechanism of such a phenomenon is carried out. First, it is found that the color features could be removed after being etched by a diluted solution of hydrochloric acid. Based on that, the hemispheric reflection spectra, surface morphology and superficial composition at different micro-areas are characterized and compared before and after being etched. The formation of the surface structures is explained by both experimental observation and simulation studies. Furthermore, based on the principles of color appearing, it is revealed that such exceptional colors are derived from surface structures, oxidation layers and material intrinsic color. The relationship between color performance and these three colorizing factors is also revealed. The method used in this study can be applied to the exploration of the coloration mechanism of other metals. In addition, the colorful surface by fs-LDW is superhydrophobic with low adhesion and anisotropic wettability, which can protect the colorized surface from contamination by self-cleaning performance and promote its practical application.

Electrochemical Surface Characterization of a Femtosecond Laser Treated and Anodized Ti and Ti6Al4V Alloy for Bone and Dental Implants

Pure Titanium (Titanium grade 2) and Ti6Al4V (Titanium grade 5) alloys are commonly used biocompatible materials for medical bone implants and dental protheses. As some implants have to be removed after a certain amount of time after the implantation, the osteo repellent surface is one of the most important property for the removable bone implants such as bone screws and plates. On contrary, for the dental protheses the property of the most importance is osseointegration. Femtosecond laser treatment causes ablation and produces LIPSS (“laser induced periodic surface structures”) which can consist of cones on macro scale and ripples on nano scale which showed structures and roughness similar to that of a bone. Therefore, surface modifications by electrochemical anodization and femtosecond laser could be seen as promising methods for improving both osteo-repellence and osteointegration properties of the bone implants and dental protheses. The aim of this work is electrochemical and surface characterization of the anodized Titanium and Ti6Al4V alloy treated by the femtosecond laser. Firstly, Titanium and Ti6Al4V samples were anodized potentiostaticaly up to 100V in 25% phosphoric acid solution for 120s. Following the potentiostatic anodization, samples were structured with femtosecond laser to produce micro cones and nano ripples on top of the cones. As a final step, laser treated spots were potentiodynamicaly anodized using a SDCM (Scanning Droplet Cell Microscopy) setup. Influence of different potentials, scan rates and electrolytes were studied and optimized, consequently. Morphology and topography were examined by the means of SEM (Scanning Electron Microscopy) and AFM (Atomic Force Microscopy), while crystallography was determined by the XRD (X-Ray Diffraction). Furthermore, the composition of the oxide layer was determined by the XPS (X-ray photoelectron spectroscopy). Oxide forming factor (kox), a relative permittivity εr, and ECSA (Electrochemical surface area) were obtained from the cyclic voltammograms (CV) and electrochemical impedance spectroscopy (EIS) experimental data. Electrochemical impedance spectroscopy data was modeled and compared between not preanodized, preanodized and anodized and not anodized after femtosecond laser structuring. Finally, bioassessment with osteoblast was done to examine the growth of the osteoblast cells on the modified surface structures. Value of the oxide forming factor (kox) for the pure Titanium and Titanium grade 5 were successfully calculated and compared with a Scanning Electron Microscopy. Calculated values of the relative permittivity εr are in agreement with the literature values. Finally, obtained results indicate that anodized and subsequently femtosecond laser treated samples could be used as medical bone and dental implants.

A solid-liquid composite electrolyte with a vertical microporous [formula omitted] skeleton that prepared by femtosecond laser structuring and filled with ionic liquid

We report a novel composite electrolyte, composed of ceramic Li1.5Al0.5Ge1.5(PO4)3 (LAGP) skeleton with tunable vertical pores and ionic liquids (IL) fillers. both components have high-safety features. The vertical ionic liquid channels that prepared by femtosecond laser shorten the lithium ion transport path and the ionic liquid on the electrolyte surface improves the wettability between the solid electrolyte and electrode material. The total impedance of the pores LAGP&IL electrolytes (PLI) is 411.6 Ω，with the ionic conductivity of 4.3 × 10−5 S/cm at room temperature. Compared with non-pores LAGP&IL electrolytes (NPLI), the total impedance is reduced by 3 times. The lithium ion transference number of PLI electrolyte is 0.53, which is in contrast to the value 0.29 of NPLI electrolyte. The full cell consisting of LiFePO4 (LFP) | composite electrolyte | Li demonstrates a specific capacity of 136.6 mAhg−1 on the first cycle of discharge at 0.1C and a capacity retention rate of 89.7% after 20 cycles at room temperature. The symmetrical battery can cycle stably for 60 h at room temperature, which is 140% longer than that of non-pores LAGP composite ionic liquid electrolyte. This work provides an insight into the high-performance electrolyte preparation and its significance in the high-safety lithium-metal battery.

Femtosecond laser texturing as a tool to increase the hydrophobicity of ornamental stone: The influence of lithology and texture

In the field of stone conservation, a very common direct intervention seeks to increase the water repellence of objects. By limiting the interaction between the solid and the water, the possibility of alteration due to the action of the water (liquid or solid) as well as that related to the colonisation of surfaces by organisms is reduced. To decrease wettability, chemicals are often applied to create a surface layer; however, laser texturing, currently used in different industrial and technological fields, could be considered as an alternative procedure, thus eliminating exposure to chemicals with varying degrees of toxicity. In this paper, modification of the wetting properties of stone surfaces upon texturing induced by a femtosecond laser structuring process was investigated. Four ornamental stones with different mineralogic and chemical compositions (slate, quartzite, granite and marble) and other surface characteristics were laser processed by applying different texturing patterns (parallel grooves and matrices of craters) and different irradiation parameters. After texturing, variations on the wettability characteristics of the different rock surfaces were evaluated by means of static contact angle measurements and modifications on the topography were studied via confocal microscopy. Furthermore, potential harmful effects on the ornamental stones were evaluated through colour spectrophotometry, petrographic microscopy and SEM-EDX. The results indicate two different behaviours in the ornamental stones analysed that were statistically confirmed: on the one hand, the group formed by slate, quartzite and granite, in which the laser texturing caused a decrease in the contact angle and, on the other hand, marble in which laser texturing was able to increase the contact angle above 90°, giving the stone surface a hydrophobic character. The topographic analyses together with microscopy observations indicate that the grain size, mineral composition, type of fissures and initial surface quality of the stones were key in the different wetting behaviour of the laser textured stones.

Long-term seawater anti-corrosion properties of Al alloy triggered by femtosecond laser structuring with phase change

Through adopting a technique of femtosecond laser micro/nano-structuring, we successfully modify the surface of aluminium alloy material into the long-term stable anti-corrosive properties, exhibiting the measured corrosion rate two orders of magnitude smaller than that of the bare sample. The underlying mechanisms are attributed to both the surface micro/nano-structure formation with the thick stable oxide layers and the significant phase change from crystalline to amorphous by the laser-induced stress and compressive strain, which consequently reduce the free energy and chemical activity of the structured surface. Such investigations may open a new eco-friendly way to produce anti-corrosive metal surfaces for deep seawater applications.

Femtosecond laser structuring of permeable and resorbable biomaterial

Abstract Bioresorbable nanofiber nonwovens with their fascinating properties provide a wide range of potential biomedical applications. Modification of the material enables the adjustment of mechanical and biological characteristics depending on the desired application. Due to the nanosized fiber network, post-production structuring is very challenging. Within this study, we use femtosecond laser technology for structuring permeable and resorbable electrospun poly-L-lactide (PLLA) membranes. We show that this post-production process can be used without disturbing the fiber network near the structured areas. Furthermore, the modification of the water permeability and mechanical characteristics due to the laser structuring was investigated. The results prove femtosecond laser technology to be a promising method for the adjustment of the membrane properties and which in consequence can help to optimize cell adhesion, enable revascularization and open up applications of nanofiber membranes in personalized medicine.

All femtosecond optical pump and x-ray probe: holey-axicon for free electron lasers

We put forward a co-axial pump (optical)-probe (x-rays) experimental concept and show performance of the optical component. A Bessel beam generator with a central 100 µm diameter hole (on the optical axis) was fabricated using femtosecond (fs) laser structuring inside a silica plate. This flat-axicon optical element produces a needle-like axial intensity distribution which can be used for the optical pump pulse. The fs-x-ray free electron laser (X-FEL) beam of sub-1 µm diameter can be introduced through the central hole along the optical axis onto a target as a probe. Different realisations of optical pump are discussed. Such optical elements facilitate alignment of ultra-short fs-pulses in space and time and can be used in light–matter interaction experiments at extreme energy densities on the surface and in the volume of targets. Full advantage of ultra-short 10 fs-X-FEL probe pulses with fs-pump (optical) opens an unexplored temporal dimension of phase transitions and the fastest laser-induced rates of material heating and quenching. A wider field of applications of fs-laser-enabled structuring of materials and design of specific optical elements for astrophotonics is presented.

Формирование и оптические свойства нанорешеток на поверхности фторида кальция, генерируемых при фемтосекундном лазерном воздействии

Femtosecond laser structuring of dielectrics is an urgent problem for the creation of optical elements. In this work, we performed femtosecond laser nanostructuring of the calcium fluoride surface with the formation of self-organizing periodic gratings with subwavelength periods of the order of 200 and 350 nm. During the work, the dependence of the period of the structures on the wavelength of laser radiation was established, which was confirmed by the simulation results. The structures show a decrease in transmission over the entire visible range, predominantly due to diffraction and light scattering. Keywords: direct laser recording, femtosecond laser pulses, surface functional nano- and micro-optical structures, diffraction.

Microconical surface structuring of aluminium tubes by femtosecond laser processing

Femtosecond laser microstructuring is a convenient technology for the targeted surface functionalization of various materials. Commonly, the structuring process is performed on planar surfaces. Here, we investigated femtosecond laser structuring of aluminium tubes. Process parameters, i.e. the number of pulses per spot on the surface and the line distance, have been transformed from a line-by-line process on planar samples towards a helical process. The process is based on laser treating the rotating tube while the laser beam is moved along the axis of the tube. A significant difference of the surface structure obtained on a cylinder in comparison to the planar geometry is revealed. With exactly matching process parameters, a strong increase of the dimensions of the surface structures on aluminium tubes has been observed. With a typical parameter set to achieve microconically structured aluminium, the cone height increases from 5 to 24 μm and the cone-to-cone distance from 13 to 59 μm. The structure sizes were found to be unaffected from the diameter of the tube within a range from 12 to 40 mm. A possible explanation for the increased structure size is given by altered particle redeposition. Two different parameter sets have been transformed from a planar geometry to the cylindrical geometry. Deep black aluminium tubes providing hydrophobicity with a water contact angle up to 148° and a thermal emissivity up to 87% are demonstrated.

Femtosecond Laser Structuring of Materials: A Review

In this review the interaction between femtosecond laser and matter with emphasis on silicon and some metals have been appraised. For silicon, spikes are produced as a result of interaction in the presence of background gas such as SF6, or H2S with an appropriate background pressure, but spikes are not formed in the presence N2 or air. The formation of the spikes increase the infrared light absorption of silicon to near unity. Interaction of femtosecond laser with metals form periodic surface structures that make the metals exhibit many different morphological characteristics. This processing technique allows the creation of a variety of colors on a metal that ultimately lead to control of its optical properties from UV to terahertz. From the assessment made, the potential of femtosecond laser structuring of materials for cost-effective nano-manufacturing is high.

Femtosecond Laser Fabrication of Engineered Functional Surfaces Based on Biodegradable Polymer and Biopolymer/Ceramic Composite Thin Films.

Surface functionalization introduced by precisely-defined surface structures depended on the surface texture and quality. Laser treatment is an advanced, non-contact technique for improving the biomaterials surface characteristics. In this study, femtosecond laser modification was applied to fabricate diverse structures on biodegradable polymer thin films and their ceramic blends. The influences of key laser processing parameters like laser energy and a number of applied laser pulses (N) over laser-treated surfaces were investigated. The modification of surface roughness was determined by atomic force microscopy (AFM). The surface roughness (Rrms) increased from approximately 0.5 to nearly 3 µm. The roughness changed with increasing laser energy and a number of applied laser pulses (N). The induced morphologies with different laser parameters were compared via Scanning electron microscopy (SEM) and confocal microscopy analysis. The chemical composition of exposed surfaces was examined by FTIR, X-ray photoelectron spectroscopy (XPS), and XRD analysis. This work illustrates the capacity of the laser microstructuring method for surface functionalization with possible applications in improvement of cellular attachment and orientation. Cells exhibited an extended shape along laser-modified surface zones compared to non-structured areas and demonstrated parallel alignment to the created structures. We examined laser-material interaction, microstructural outgrowth, and surface-treatment effect. By comparing the experimental results, it can be summarized that considerable processing quality can be obtained with femtosecond laser structuring.

Bioinspired Hierarchical Surfaces Fabricated by Femtosecond Laser and Hydrothermal Method for Water Harvesting.

The world is facing a global issue of water scarcity where two-thirds of the population does not have access to safe drinking water. Water harvesting from the ambient environment has a potential equivalent to ∼10% of the fresh water available on the earth's surface, but its efficiency requires a special control of surface morphology. We report a novel facile physicochemical hybrid method that combines femtosecond laser structuring with hydrothermal treatment to create a surface with a well-arranged hierarchical nanoneedle structures. Polydimethylsiloxane treatment of the thus-produced hierarchical structures nurtured superhydrophobic functionality with a very low water sliding angle (∼3°) and a high water adhesion ability. About 2.2 times higher water-collection efficiency was achieved using hierarchical structures over untreated flat Ti surfaces of the same area under a given experimental condition. The comparison of water-collection behavior with other samples showed that the improved efficiency is due to the structure, and wettability induced superior water attraction and removal ability. Moreover, a uniform water condensation under low humidity (28%) is achieved, which has potential applications in harvesting water from arid environments and in high-precision drop control.