One-step Femtosecond Laser Research Articles

One-Step Femtosecond Laser Stealth Dicing of Quartz.

We report on a one-step method for cutting 250-µm-thick quartz plates using highly focused ultrashort laser pulses with a duration of 200 fs and a wavelength of 1030 nm. We show that the repetition rate, the scan speed, the pulse overlap and the pulse energy directly influence the cutting process and quality. Therefore, a suitable choice of these parameters was necessary to get single-pass stealth dicing with neat and flat cut edges. The mechanism behind the stealth dicing process was ascribed to tensile stresses generated by the relaxation of the compressive stresses originated in the laser beam focal volume during irradiation in the bulk material. Such stresses produced micro-fractures whose controlled propagation along the laser beam path led to cutting of the samples.

Spontaneous and unidirectional transportation of underwater bubbles on superhydrophobic dual rails

Superhydrophobic/superhydrophilic surfaces (SBS/SLS) with excellent water repellency/adhesion are important in both academic research and industrial settings owing to their intriguing functions in tiny droplet and gas bubble manipulation. However, most manipulation strategies involving SBS/SLS are limited to their large-area fabrication or sophisticated morphology designs, which distinctly hinders their practical uses. In this paper, we design and fabricate superhydrophobic polydimethylsiloxane narrowing dual rails (SNDRs) beneath a superhydrophilic stainless steel sheet by one-step femtosecond laser ablation. Our SNDR tracks are capable of transporting gas bubbles in various volumes from wide end to narrow end spontaneously and unidirectionally underwater, even when they are bent. The mechanical analysis for diverse geometrical dual-rail configurations in bubble transportation performance is further discussed. Finally, we experimentally demonstrate the intriguing capability of lossless mixing of gas bubbles at a designed volume ratio on a multiple SNDR combination. This approach is facile and flexible, and will find broad potential applications such as intelligent bubble transport, mixing, and controllable chemical reactions in interfacial science and microfluidics.

Biocompatible nano-ripples structured surfaces induced by femtosecond laser to rebel bacterial colonization and biofilm formation

Structured surfaces with both anti-bacterial capability and biocompatibility are essential to medical devices including orthopedic implants. Over the past few years, numerous studies indicated that nanostructures such as nanotubes, nanowires, nano-pillars and nano-ripples were capable of repelling or killing bacteria, while the morphology and dimensions of the nanostructures showed essential influence on the adhesion and proliferation of cells. The long-term functionalities of implants depend on their reliable anti-bacterial performance at the same time enhanced biocompatibility. However, researches covering both these two aspects are still very limited. In this paper, we applied one-step femtosecond laser irradiation to produce three types of nano-ripples, and to investigate their anti-bacterial behavior and their biocompatibility. Our results demonstrate that all the three types of nano-ripples are capable of preventing bacterial colonization and biofilm formation, with their anti-bacteria rates towards E. coli respectively 43%, 49% and 56%. Meanwhile, the femtosecond laser induced nano-ripples exhibit good rat mesenchymal stem cells (MSCs) proliferation capacity and spreading performance, and the nano-ripples affect significantly the orientation of MSCs. The results offer valuable information and potentials on the anti-bacteria and biocompatibility of nanostructures.

Photothermal Actuation of Diverse Liquids on an Fe3O4-Doped Slippery Surface for Electric Switching and Cell Culture.

The photoinduced manipulation of liquids on a slippery lubricant-infused porous surface (SLIPS) has attracted a tremendous amount of attention because of its merits of contactless stimulation and excellent spatial and temporal control. However, tedious fabrication methods by a combination of template transfer and fluorination for a photothermal-material-doped SLIPS and the lack of deeper systematically quantitative analysis with respect to droplet hydrokinetics are greatly perplexing in both academic research and industrial applications. Here we demonstrate a kind of Fe3O4-doped SLIPS by one-step femtosecond laser cross-scanning, which can readily steer diverse liquids toward arbitrary directions with a fast velocity of up to 1.15 mm/s in the presence of a unilateral NIR stimulus. The underlying mechanism is that the wettability gradient force (Fwet-grad) induced by the temperature gradient arising from asymmetric near-infrared-irradiation (NIR) loading would be generated within 1 s to actuate a targeted droplet's sliding behavior. Through tuning the NIR irradiating sites, we can slide a targeted droplet with controllable directions and routes. On the basis of fundamental physics, we have quantitatively analyzed the relationship among Fe3O4-doped content, lubricant rheological performance, droplet wettability variations, Fwet-grad, and the sliding velocity for diverse liquid species. Accordingly, we can remotely steer liquid droplets to realize the on-off state of an electrical circuit on demand, the droplet fusion of a microfluidic reactor, and the culture/inhibition of biological cells.

Anisotropic Sliding of Underwater Bubbles On Microgrooved Slippery Surfaces by One-Step Femtosecond Laser Scanning.

Slippery liquid-infused surfaces (SLIPS) with excellent liquid sliding abilities have attracted great attention due to their multifunctions in broad fields. However, current research is mainly concentrated on the isotropic SLIPS, and there are few studies about the fabrication of anisotropic SLIPS and the investigation of anisotropic bubble sliding. Herein, we reported a kind of distinct periodic microgrooved slippery surface (MGSS) by one-step femtosecond laser scanning and realized bubble anisotropic sliding in a liquid system. The MGSS enables the bubble to slide along the direction of grooves but prevents the bubble from sliding along the perpendicular direction to the groove. The mechanism is mainly related to the energy barrier difference caused by the spin-coating oil film thickness and the groove height along the parallel and perpendicular directions. The relationship between the driven force of buoyancy and the resistance of contact angle hysteresis was investigated by theoretical analysis, and the theoretical prediction showed a great adherence with the experimental results. We also studied the influence of laser power and groove period on the degree of anisotropy, and it was found that the groove space has little effect on the degree of anisotropy and the strongest bubble anisotropy can reach nearly 80°. Finally, the MGSS was successfully used in anisotropic bubble transportation on flat and curved surfaces. We believe that such functional surfaces will be promising candidates for manipulating bubble directional sliding behavior and further underwater gas collection.

Femtosecond Laser-Assisted Synthesis of ZnO Nanoparticles in Solvent with Visible Emission for Temperature Sensing

Zinc oxide (ZnO) nanoparticles (NPs) are synthesized by one-step femtosecond laser ablation of zinc powders in n-methyl pyrrolidone (NMP) at room temperature. The as-prepared ZnO NPs are fairly stable, water-soluble and have abundant surface functional groups resulting in a strong fluorescence in the visible region. By further annealing the ZnO NPs in the reacting solvent up to 120∘C, the photoluminescence (PL) intensity of material can be significantly enhanced. Besides, the PL of ZnO NPs can change from blue to green by controlling the annealing temperature. The products exhibit excellent temperature sensing with high temperature sensitivity and a 1.3% change per∘C response over a linear temperature sensing range (6–84[Formula: see text] in aqueous buffer, which matches well with the physiologically relevant temperatures. Hence, the ZnO nanoparticle system can serve as a promising candidate for practical fluorescent temperatures nanosensors which can be used for accurate temperature monitoring within biological systems.

One-step femtosecond laser ablation synthesis of sub-3 nm gold nanoparticles stabilized by silica

We report the synthesis of silica-gold nanoparticles (silica-Au NPs) using a one-step femtosecond-reactive laser ablation in liquid (fs-RLAL) technique by focusing femtosecond laser pulses onto a silicon wafer immersed in an aqueous KAuCl4 solution. Characterization of the silica-Au NPs revealed two populations of Au NPs: (i) larger, isolated Au NPs with diameter 7.0 ± 2.0 nm, and (ii) smaller Au NPs (1.9 ± 0.7 nm) stabilized by an amorphous silica matrix, along with new species of silicon observed from XPS analysis. The silica-Au NPs were catalytically active towards the model reaction of para-nitrophenol reduction by NaBH4. The formation of the two populations of silica-Au NPs is ascribed to reaction dynamics occurring on two distinct timescales. First, the dense electron plasma formed within tens of femtoseconds of the laser pulse initiates reduction of the [AuCl4]− complex, leading to the formation of larger isolated Au NPs. Second, silicon species ejected from the wafer surface hundreds of picoseconds or later after the initial laser pulse reduce the remaining [AuCl4]− and encapsulate the growing clusters, forming ultrasmall Au NPs stabilized by the silica matrix. The morphologies of the silica-Au NPs generated from fs-RLAL are distinct from those reported in recent RLAL experiments with nanosecond lasers, reflecting distinct mechanisms occurring on the different pulse duration timescales.

Laser Structuring of Underwater Bubble-Repellent Surface.

Bubbles in aqueous media are pervasive and unavoidable. However, underwater gas bubbles adhesion to the metal pipework can sometimes seriously damage the surface and reduce the useful life of devices. Herein, we report a simple way to fabricate underwater bubble-repellent surface by one-step femtosecond laser direct writing technology. The as-prepared surface exhibits superhydrophilicity in air and superaerophobicity in water, and the bubble contact angles reach 159±2.5° in water. The surface presents ultralow bubble adhesion, and the rolling angle of the bubble is small. The potential mechanism is also discussed. This method offers an easy route to prepare underwater superaerophobic surfaces with ultralow bubble adhesion, and it has potential applications in underwater bubble-repelling facilities.

Ultrafast Achievement of a Superhydrophilic/Hydrophobic Janus Foam by Femtosecond Laser Ablation for Directional Water Transport and Efficient Fog Harvesting.

Water scarcity is a serious global challenge, especially in arid and desert regions. Functional devices for directional water transport and fog collection have received increasing attention. Existing methods and technologies suffer from low fog-collecting efficiencies, complicated fabrication processes, and high fabrication costs. Herein, we report a simple and low-cost method to rapidly fabricate nanoparticle-covered microstructures on one side of a copper foam surface, using one-step femtosecond laser direct writing technology, which enormously improved processing efficiency. The resulting foam exhibits superhydrophilic/hydrophobic Janus properties. The foam allows water droplets to pass from the hydrophobic side to the superhydrophilic side, but not in the opposite direction. The Janus foam can therefore be used for harvesting water in fog environments, and the maximum water-collecting efficiency is 3.7 g cm-2 h-1, which is much better than existing data. The Janus foam exhibits excellent stability during abrasion and hydraulic wash tests. This water-collecting design may provide an efficient route for overcoming future water shortages.

Patternable fabrication of hyper-hierarchical metal surface structures for ultrabroadband antireflection and self-cleaning

The capabilities to reduce light reflection have essential importance for various critical applications. Realistic antireflection surfaces are required to satisfy the comprehensive demands in broadband effectiveness, flexible fabrication, and performance stability. Here, we propose and experimentally demonstrate a type of highly disordered hyper-hierarchical micro-nano structures formed on the surfaces of metals such as Cu, which have the significant capability in absorbing light over the ultrabroadband spectrum from ultraviolet to far-infrared. Average hemispherical reflectance of ∼2.4%, ∼5.5%, and ∼6% is achieved in the wavelength ranges of 400–800 nm, 200–2000 nm, and 2.5–25 μm, respectively, reaching an average absorptance of ∼94% within 0.2–25 μm. The specular reflectance in the long wavelength range of 25–300 μm is also dramatically reduced with respect to the original Cu surface. Such an ultrabroadband antireflection structure is fabricated by a non-contact, maskless, one-step femtosecond laser direct writing approach, making it flexible to be prepared in desired patterns. The hyper-hierarchical structure and its ultrabroadband antireflection property keep robust and stable during harsh aging tests. In addition to the antireflection property, the hyper-hierarchical structure also exhibits excellent self-cleaning performance. All these advantages in ultrabroadband effectiveness, patterning flexibility, structural robustness, as well as self-cleaning, make it promising for practical applications.

Robust laser-structured asymmetrical PTFE mesh for underwater directional transportation and continuous collection of gas bubbles

We report a simple, efficient method to fabricate micro/nanoscale hierarchical structures on one side of polytetrafluoroethylene mesh surfaces, using one-step femtosecond laser direct writing technology. The laser-treated surface exhibits superhydrophobicity in air and superaerophilicity in water, resulting in the mesh possessing the hydrophobic/superhydrophobic asymmetrical property. Bubbles can pass through the mesh from the untreated side to the laser-treated side but cannot pass through the mesh in the opposite direction. The asymmetrical mesh can therefore be designed for the directional transportation and continuous collection of gas bubbles in aqueous environments. Furthermore, the asymmetrical mesh shows excellent stability during corrosion and abrasion tests. These findings may provide an efficient route for fabricating a durable asymmetrical mesh for the directional and continuous transport of gas bubbles.

Multifunctional oil-water and immiscible organic liquid separation by micropore arrayed Ti foil

In this work a multifunctional micropore array (size from 5 to 42 μm) was produced by using one-step femtosecond laser microdrilling for oil-water and oil-oil separation. This novel method has many advantages, such as high precision (size error is less than 1 μm), simple operation (one step), extensible function (even complex microstructures) just to name a few. The prepared foil exhibited superhydrophilic and underwater superoleophobic properties, which can be used to separate the light oil (C8H18) and water mixtures. After heating in dark environment 0.5 h, the prepared foil showed superhydrophobic and underwater superoleophilic properties, and can be used to separate the heavy oil (C2H4Cl2) and water mixtures. In addition, the heated sample also showed robust ability to separate the immiscible organic liquid mixtures (formamide and C2H4Cl2), exhibiting multifunctional applications. Interestingly, the heated samples would recover its original superhydrophilicity after UV irradiation in ethanol for 1 h. The samples don’t contain any fluorinated compounds and display environmental stability even after sonic cleaning and scratch. This work will provide a new insight into the design of intelligent devices for oil/water mixtures separation, organic liquid mixtures separation, and water droplet manipulation.

Porous Network Microstructures: Femtosecond Laser Direct Writing of Porous Network Microstructures for Fabricating Super‐Slippery Surfaces with Excellent Liquid Repellence and Anti‐Cell Proliferation (Adv. Mater. Interfaces 7/2018)

Porous network microstructures can be directly generated on various polymer surfaces by one-step femtosecond laser writing. Inspired by Nepenthes pitcher plant, a super-slippery surface was fabricated based on the porous PET substrate whose surface was fully covered by interconnected nanopores. The resultant slippery surface can repel various liquids. In addition, such a surface can completely inhibit the cells growth. This is reported by Feng Chen, Xiaoyun Lu and co-workers in article number 1701479.

Femtosecond laser fabrication of a gradient-wettability mesh for spilled oil crossflow collection

Efficient continuous clean-up of large-scale oil spills is a global challenge. Herein, we present a simple method for fabrication of a gradient-wettability hydrophilic tilted mesh for fast spilled oil crossflow collection. After one-step femtosecond laser irradiation, the gradient-wettability mesh is tightly assembled and consists of four different pore size meshes, which possesses nanoripple structures. Meanwhile, the gradient-wettability mesh has a higher oil collection rate than single wettability meshes. This femtosecond-laser-induced gradient-wettability mesh design will have practical applications for efficient crossflow collection of large-area oil spills.

One-step micro-modification of optical properties in silver-doped zinc phosphate glasses by femtosecond direct laser writing

We demonstrate the possibility of joint formation of fluorescent silver clusters and plasmonic silver nanoparticles spatially confined in micron-sized domains by the one-step femtosecond direct laser writing (DLW) without subsequent heat treatment in zinc phosphate glasses with different concentration of silver. We show that DLW in glass induces local micro-modification of optical properties resulted in the appearance of luminescence, absorption and form birefringence in domains. Variation of laser pulse energy allows controlling the micro-modification process and tuning of optical properties. We propose a possible mechanism for observed phenomena that includes local chemical redistribution of glass network modifiers during DLW process. We believe that ability to form complex 3D shapes of luminescent, plasmonic and birefringent structures embedded in dielectric transparent glass materials opens new routes for the design of nanophotonic devices and multidimensional optical memory.

A facile strategy to integrate robust porous aluminum foil into microfluidic chip for sorting particles

High efficiency integration of functional microdevices into microchips is crucial for broad microfluidic applications. Here, a device-insertion and pressure sealing method was proposed to integrate robust porous aluminum foil into a microchannel for microchip functionalization which demonstrate the advantage of high efficient foil microfabrication and facile integration into the microfluidic chip. The porous aluminum foil with large area (10 × 10 mm2) was realized by one-step femtosecond laser perforating technique within few minutes and its pores size could be precisely controlled from 3 μm to millimeter scale by adjusting the laser pulse energy and pulse number. To verify the versatility and flexibility of this method, two kinds of different microchips were designed and fabricated. The vertical-sieve 3D microfluidic chip can separate silicon dioxide (SiO2) microspheres of two different sizes (20 and 5 μm), whereas the complex stacking multilayered structures (sandwich-like) microfluidic chip can be used to sort three different kinds of SiO2 particles (20, 10 and 5 μm) with ultrahigh separation efficiency of more than 92%. Furthermore, these robust filters can be reused via cleaning by backflow (mild clogging) or disassembling (heavy clogging).

One-step femtosecond laser welding and internal machining of three glass substrates

In this paper, it demonstrated one-step femtosecond laser welding and internal machining of three fused silica substrates in the optical- and non-optical-contact regimes by focusing 1030-nm laser pulses at the middle of the second substrate. Focusing laser pulses within the second glass in optical-contact and non-optical-contact samples induces permanent internal structural modification, leading to the three glass substrates bonding together simultaneously. The bonding mechanism is based on the internal modification of glass, and this mechanism is different from that of ordinary glass welding at the interface. Welding-spot size is affected by not only the gap distance (ablation effect) and heat transmission, but also by gravity through examining the sizes of the welding spots on the four contact welding surfaces. The maximum bonding strength of the lower interface (56.2 MPa) in the optical-contact regime is more than double that (27.6 MPa) in the non-optical-contact regime.

One-step synthesis of nitrogen-doped carbon nanodots for ratiometric pH sensing by femtosecond laser ablation method

Nitrogen-doped carbon nanodots (CDs) are synthesized by one-step femtosecond laser ablation of graphite powder in aminotoluene at room temperature. The as-prepared CDs have the average diameter of 2.87nm and possess an excitation-independent emission covering nearly the whole visible light region at a single excitation wavelength. The X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) analysis indicate that there are a huge number of multiple oxygen groups and amine groups on the surface of the CDs. As their different fluorescence peaks originated from different emission surface groups on the nanodots show different pH dependence, these CDs can be used for ratiometric pH sensing.

An anti-reflective 1D rectangle grating on GaAs solar cell using one-step femtosecond laser fabrication

We report the fabrication of the anti-reflective micro/nano-structure on absorbing layer of GaAs solar cell surface using an efficient approach based on one-step femtosecond laser irradiation. Morphology of the microstructures and reflectance of the cell irradiated are characterized with SEM and spectrometer to analyze the influence of laser processing parameters on the change of microstructures induced and the reflectance. It has been found that the rectangle grating micro/nano-structure with a period of 700nm and width of 600nm is obtained neatly with laser pulse energy of 30.5μJ(pulse duration is 130fs, center wavelength is 800nm, scanning speed is 2.2mm/s and spot diameter is 22µm). Reflectance has been suppressed to 23.6% with rectangle structure from 33% of planar cell. In addition, simulation using a finite-difference-time domain(FDTD) method results show that the rectangle grating micro/nano-structure can effectively suppress the reflection within large wavelength ranges.

Internal and External Flow over Laser-Textured Superhydrophobic Polytetrafluoroethylene (PTFE).

In this work, internal and external flows over superhydrophobic (SH) polytetrafluoroethylene (PTFE) were studied. The SH surface was fabricated by a one-step femtosecond laser micromachining process. The drag reduction ability of the textured surface was studied experimentally both in microscale and macroscale internal flows. The slip length, which indicates drag reduction in fluid flow, was determined in microscale fluid flow with a cone-and-plate rheometer, whereas a pressure channel setup was used for macroscale flow experiments. The textured PTFE surface reduced drag in both experiments yielding comparable slip lengths. Moreover, the experimentally obtained slip lengths correspond well to the result obtained applying a semianalytical model, which considers the solid fraction of the textured surface. In addition to the internal flow studies, we fabricated SH PTFE spheres to test their drag reduction abilities in an external flow experiment, where the terminal velocities of the falling spheres were measured. These experiments were conducted at three different Reynolds numbers in both viscous and inertial flow regimes with pure glycerol, a 30% glycerol solution, and water. Surprisingly, the drag on the SH spheres was higher than the measured drag on the non-SH spheres. We hypothesize that the increase in form drag outweighs the decrease in friction drag on the SH sphere. Thus, the overall drag increased. These experiments demonstrate that a superhydrophobic surface that reduces drag in internal flow might not reduce drag in external flow.