High-speed femtosecond laser plasmonic lithography and reduction of graphene oxide for anisotropic photoresponse

Ultrafast Laser Processing of 2D Materials: Novel Routes to Advanced Devices

Ultrafast laser processing has emerged as a versatile technique for modifying materials and introducing novel functionalities. Over the past decade, this method has demonstrated remarkable advantages in the manipulation of 2D layered materials, including synthesis, structuring, functionalization, and local patterning. Unlike continuous-wave and long-pulsed optical methods, ultrafast lasers offer a solution for thermal heating issues. Nonlinear interactions between ultrafast laser pulses and the atomic lattice of 2D materials substantially influence their chemical and physical properties. This paper highlights the transformative role of ultrafast laser pulses in maskless green technology, enabling subtractive, and additive processes that unveil ways for advanced devices. Utilizing the synergetic effect between the energy states within the atomic layers and ultrafast laser irradiation, it is feasible to achieve unprecedented resolutions down to several nanometers. Recent advancements are discussed in functionalization, doping, atomic reconstruction, phase transformation, and 2D and 3D micro- and nanopatterning. A forward-looking perspective on a wide array of applications of 2D materials, along with device fabrication featuring novel physical and chemical properties through direct ultrafast laser writing, is also provided.

Droplet Manipulation on Bioinspired Slippery Surfaces: From Design Principle to Biomedical Applications

Droplet manipulation with high efficiency, high flexibility, and programmability, is essential for various applications in biomedical sciences and engineering. Bioinspired liquid-infused slippery surfaces (LIS), with exceptional interfacial properties, have led to expanding research for droplet manipulation. In this review, an overview of actuation principles is presented to illustrate how materials or systems can be designed for droplet manipulation on LIS. Recent progress on new manipulation methods on LIS is also summarized and their prospective applications in anti-biofouling and pathogen control, biosensing, and the development of digital microfluidics are presented. Finally, an outlook is made on the key challenges and opportunities for droplet manipulation on LIS.

Optimization of Novel 2D Material Based SPR Biosensor Using Machine Learning

Biosensors are needed for today's health monitoring system for detecting different biomolecules. Graphene is a monolayer material that can be utilized to sense biomolecules and design biosensors. We have proposed a Graphene-Gold-Silver hybrid structure design based on Zinc Oxide which gives sensitive performance to detect hemoglobin biomolecules. The advanced biosensor designed based on this hybrid structure shows the highest sensitivity of 1000 nm/RIU which is far better concerning similar structure previously analyzed. The graphene-gold-silver hybrid structure is presented for its possible reflectance results and electric field results. The E-field results match well with the reflectance results given by the sensitive hybrid structure. The sensing biomolecules are presented above the structure where a combination of graphene-gold-silver hybrid structure improves the sensitivity to a great extent. The optimized parameters are obtained by applying variations in the physical parameters of the design. The machine learning algorithm employed for reflectance prediction shows a high prediction accuracy and can be utilized for simulation resource reduction. The proposed biosensor can be used in real-time hemoglobin monitoring.

Regulation of laser-induced nanogratings by tuning the Marangoni-plasmon-coupled effect

Laser-induced subwavelength nanogratings on films find widespread applications in enhancing a spectrum through surface plasmon excitation. It is challenging to achieve high uniformity, diversity, and controllability due to the intricate interplay between two basic mechanisms in laser nanostructuring: the Marangoni effect and surface plasmon polaritons (SPPs). We tune the coupled effect on Ge2Sb2Te5 films by adjusting the laser polarization, whose component controls the two effects' strength ratio. The Marangoni effect dominates when the SPPs' direction mismatches with the growing direction of nanogratings. Tuning this competition relationship helps to create nanogratings with tunable duty cycle and distribution, which are significant for light modulation applications. A highly efficient direct writing method with a line-shaped laser beam is employed to create large-area regular nanogratings by enhancing the effect tuning. We demonstrate diverse Au nanogratings with the aid of a lift-off operation and apply them in surface plasmon-coupled emission (SPCE), showcasing exceptional enhancement and narrowing performance.

High-power 100 W Kerr-lens mode-locked ring-cavity femtosecond Yb:YAG thin-disk oscillator

High-power femtosecond pulses delivered at a high-repetition rate will aid machining throughput and improve signal-to-noise ratios for sensitive measurements. Here we demonstrate a Kerr-lens mode-locked femtosecond Yb:YAG ring-cavity thin-disk oscillator with a multi-pass scheme for the laser beam. With four passes through the thin disk, 175-fs pulses were delivered from the oscillator at an average power of 71.5 W and a repetition rate of 65.3 MHz. The corresponding intra-cavity peak power of 110 MW is ample for intra-cavity nonlinear conversion into more exotic wavelength ranges. With six passes, the average output power reached 101.3 W. To the best of our knowledge, this is the highest average output power of any mode-locked ring laser. These results confirm the viability of using multi-pass configuration on a thin-disk ring oscillator for high-throughput femtosecond applications.

Low-Dimensional-Materials-Based Photodetectors for Next-Generation Polarized Detection and Imaging

The vector characteristics of light and the vectorial transformations during its transmission lay a foundation for polarized photodetection of objects, which broadens the applications of related detectors in complex environments. With the breakthrough of low-dimensional materials (LDMs) in optics and electronics over the past few years, the combination of these novel LDMs and traditional working modes is expected to bring new development opportunities in this field. Here, the state-of-the-art progress of LDMs, as polarization-sensitive components in polarized photodetection and even the imaging, is the main focus, with emphasis on the relationship between traditional working principle of polarized photodetectors (PPs) and photoresponse mechanisms of LDMs. Particularly, from the view of constitutive equations, the existing works are reorganized, reclassified, and reviewed. Perspectives on the opportunities and challenges are also discussed. It is hoped that this work can provide a more general overview in the use of LDMs in this field, sorting out the way of related devices for "more than Moore" or even the "beyond Moore" research.

Sub-diffraction limited nanogroove fabrication of 30 nm features on diamond films using 800 nm femtosecond laser irradiation

By controlling the 800 nm fs laser energy and applying an isopropyl alcohol environment, controlled sub-diffraction limited lithography with a characteristic structure of approximately 30 nm was achieved on the surface of diamond films, and diamond gratings with a period of 200 nm were fabricated. The fabrication of single grooves with a feature size of 30 nm demonstrates the potential for patterning periodic or nonperiodic structures, and the fabrication of 200 nm periodic grating structures demonstrates the ability of the technique to withstand laser proximity effects. This enhances the technology of diamond film nanofabrication and broadens its potential applications in areas such as optoelectronics and biology.

Femtosecond Laser Direct Writing of Flexible Electronic Devices: A Mini Review

By virtue of its narrow pulse width and high peak power, the femtosecond pulsed laser can achieve high-precision material modification, material additive or subtractive, and other forms of processing. With additional good material adaptability and process compatibility, femtosecond laser-induced application has achieved significant progress in flexible electronics in recent years. These advancements in the femtosecond laser fabrication of flexible electronic devices are comprehensively summarized here. This review first briefly introduces the physical mechanism and characteristics of the femtosecond laser fabrication of various electronic microdevices. It then focuses on effective methods of improving processing efficiency, resolution, and size. It further highlights the typical progress of applications, including flexible energy storage devices, nanogenerators, flexible sensors, and detectors, etc. Finally, it discusses the development tendency of ultrashort pulse laser processing. This review should facilitate the precision manufacturing of flexible electronics using a femtosecond laser.

High-Transmission Biomimetics Structural Surfaces Produced via Ultrafast Laser Manufacturing

Inspired by periodically aligned micro/nanostructures on biological surfaces, researchers have been fabricating biomimetic structures with superior performance. As a promising and versatile tool, an ultrafast laser combined with other forms of processing technology has been utilized to manufacture functional structures, e.g., the biomimetic subwavelength structures to restrain the surface Fresnel reflectance. In this review paper, we interpret the biomimetic mechanism of antireflective subwavelength structures (ARSSs) for high-transmission windows. Recent advances in the fabrication of ARSSs with an ultrafast laser are summarized and introduced. The limitations and challenges of laser processing technology are discussed, and the future prospects for advancement are outlined, too.

Rapid Electrohydrodynamic-Driven Pattern Replication over a Large Area via Ultrahigh Voltage Pulses

Despite the prospects of electrohydrodynamic instability patterning (EHIP), poor process parameter controllability is a significant challenge in uniform large-scale nanopatterning. Herein, we introduce a EHIP process using an ultrahigh electric field (>108 V/m) to effectively accelerate the pattern growth evolution. Owing to the strong dependence on a temporal parameter (1/τm) of the field strength, our method not only reduces the completion time of pattern growth but also overcomes critical parametric restrictions on the pattern replication, thereby enhancing the replicated pattern quality in three dimensions. The pattern can be uniformly replicated over the entire film surface even without a perfectly uniform air gap, which has been severely difficult in the conventional method. To further demonstrate how straightforward yet versatile our approach is, we applied our EHIP approach to successfully replicate the densely packed nanostructures of cicada wings.

Femtosecond Laser-Driven Phase Engineering of WS2 for Nano-Periodic Phase Patterning and Sub-ppm Ammonia Gas Sensing

Laser-driven phase transition of 2D transition metal dichalcogenides has attracted much attention due to its high flexibility and rapidity. However, there are some limitations during the laser irradiation process, especially the unsatisfied surface ablation, the inability of nanoscale phase patterning, and the unexploited physical properties of new phase. In this work, the well-controlled femtosecond (fs) laser-driven transformation from the metallic 2M-WS2 to the semiconducting 2H-WS2 is reported, which is confirmed to be a single-crystal to single-crystal transition without layer thinning or obvious ablation. Moreover, a highly ordered 2H/2M nano-periodic phase transition with a resolution of ≈435 nm is achieved, breaking through the existing size bottleneck of laser-driven phase transition, which is attributed to the selective deposition of plasmon energy induced by fs laser. It is also demonstrated that the achieved 2H-WS2 after laser irradiation contains rich sulfur vacancies, which exhibits highly competitive ammonia gas sensing performance, with a detection limit below 0.1 ppm and a fast response/recovery time of 43/67 s at room temperature. This study provides a new strategy for the preparation of the phase-selective transition homojunction and high-performance applications in electronics.

Three-dimensional patterning of MoS2 with ultrafast laser

Transition metal chalcogenides, a special two-dimensional (2D) material emerged in recent years, possess unique optoelectronic properties and have been used to fabricate various optoelectronic devices. While it is essential to manufacture multifunctional devices with complex nanostructures for practical applications, 2D material devices present a tendency toward miniaturization. However, the controllable fabrication of complex nanostructures on 2D materials remains a challenge. Herein, we propose a method to create designed three-dimensional (3D) patterns on the MoS2 surface by modulating the interaction between an ultrafast laser and MoS2. Three different nanostructures, including flat, bulge, and craters, can be fabricated through laser-induced surface morphology transformation, which is related to thermal diffusion, oxidation, and ablation processes. The MoS2 field effect transistor is fabricated by ultrafast laser excitation which exhibits enhanced electrical properties. This study provides a promising strategy for 3D pattern fabrication, which is helpful for the development of multifunctional microdevices.

Efficient fabrication of infrared antireflective microstructures on a curved Diamond-ZnS composite surface by using femtosecond Bessel-like beams

Antireflective microstructures fabricated using femtosecond laser possess wide-ranging applicability and high stability across different spectral bands. However, due to the limited aspect ratio of the focused light field, traditional femtosecond laser manufacturing faces challenges in efficiently fabricating antireflective microstructures with high aspect ratio and small period, which are essential for antireflection, on curved surfaces. In this study, we present a robust and efficient method for fabricating high-aspect-ratio and basal surface insensitive antireflective microstructures using a spatially shaped Bessel-like beam. Based on theoretical simulation, a redesigned telescopic system is proposed to flexibly equalize the intensity of the Bessel beam along its propagation direction, facilitating the fabrication of antireflective subwavelength structures on the entire convex lens. The fabricated microstructures, featuring a width of less than 2 µm and a depth of 1 µm, enhance transmittance from 75% to 85% on Diamond-ZnS composite material (D-ZnS) surfaces. Our approach enables the creation of high aspect ratio subwavelength structures with a z-position difference exceeding 600 µm. This practical, efficient, and cost-effective method is facilitated for producing antireflective surfaces on aero-optical components utilized in aviation.

Formation of Multiscale Pattern Structures by Combined Patterning of Nanotransfer Printing and Laser Micromachining

Various lithography techniques have been widely used for the fabrication of next-generation device applications. Micro/nanoscale pattern structures formed by lithographic methods significantly improve the performance capabilities of the devices. Here, we introduce a novel method that combines the patterning of nanotransfer printing (nTP) and laser micromachining to fabricate multiscale pattern structures on a wide range of scales. Prior to the formation of various nano-in-micro-in-millimeter (NMM) patterns, the nTP process is employed to obtain periodic nanoscale patterns on the target substrates. Then, an optimum laser-based patterning that effectively engraves various nanopatterned surfaces, in this case, spin-cast soft polymer film, rigid polymer film, a stainless still plate, and a Si substrate, is established. We demonstrate the formation of well-defined square and dot-shaped multiscale NMM-patterned structures by the combined patterning method of nTP and laser processes. Furthermore, we present the generation of unusual text-shaped NMM pattern structures on colorless polyimide (CPI) film, showing optically excellent rainbow luminescence based on the configuration of multiscale patterns from nanoscale to milliscale. We expect that this combined patterning strategy will be extendable to other nano-to-micro fabrication processes for application to various nano/microdevices with complex multiscale pattern geometries.

Optical near fields for ablation of periodic structures

The formation mechanism of laser-induced periodic surface structures (LIPSS) has been a key to high-resolution sub-diffraction lithography or high-efficiency large-area nanotexturing. We show the evolution of LIPSS formation from a nanohole seed structure to high-spatial-frequency LIPSS by using a tightly focused and rectangular-shaped laser beam with different shape-polarization orientations. Formation of LIPSS based on light intensity distribution without invoking any long-range electromagnetic modes achieved quantitative match between modeling and experiment. Our results clearly show the entire step-like and deterministic process of LIPSS evolution based on experimental data and numerical simulations, revealing the dominant structural near-field enhancement on the ripple formation. A rectangular-shaped beam with an aspect ratio of 7:3 was used to break the symmetry of a circularly shaped focus. By azimuthally rotating the orientation of the focal spot and the polarization, it is possible to visualize the far-field effect for the initial seed structure formation and the competition between the far and near fields in the subsequent structure evolution.

Development of periodically concentric rings within microcavity upon femtosecond laser irradiation

Understanding the formation mechanisms of the nanostructures and their designs has important implications for both the fundamental science and application prospects. In this study, we proposed a strategy for femtosecond laser-induced high regularity concentric rings within silicon microcavity. The morphology of the concentric rings can be flexibly modulated by the pre-fabricated structures and the laser parameters. The physics involved is deeply explored by the Finite-Difference-Time-Domain simulations, which reveals that the formation mechanism can be attributed to the near-field interference of the incident laser and the scattering light from the pre-fabricated structures. Our results provide a new method for creating the designable periodic surface structures.

Broadband and Efficient Metamaterial Absorber Design Based on Gold-MgF2-Tungsten Hybrid Structure for Solar Thermal Application

We have presented a solar absorber design with gold-MgF₂-tungsten materials. The solar absorber design is optimized with nonlinear optimization mathematical method to find and optimize geometrical parameters. The wideband absorber is made of a three-layer structure composed of tungsten, magnesium fluoride, and gold. This study analyzed the absorber's performance using numerical methods over the sun wavelength range of 0.25 μm to 3 μm. The solar AM 1.5 absorption spectrum is a benchmark against which the proposed structure's absorbing characteristics are evaluated and discussed. It is necessary to analyze the behavior of the absorber under a variety of various physical parameter conditions in order to determine the results and structural dimensions that are optimal. The nonlinear parametric optimization algorithm is applied to obtain the optimized solution. This structure can absorb more than 98% of light across the near-infrared and visible light spectrums. In addition, the structure has a high absorption efficiency for the far range of the infrared spectrum and the THz range. The absorber that has been presented is versatile enough to be used in a variety of solar applications, both narrowband and broadband. The design of the solar cell that has been presented will be of assistance in designing a solar cell that has high efficiency. The proposed optimized design with optimized parameters will help design solar thermal absorbers.

Nanoscale control of non-reciprocal ripple writing

Femtosecond laser-induced deep-subwavelength structures have attracted much attention as a nanoscale surface texturization technique. A better understanding of the formation conditions and period control is required. Herein, we report a method of non-reciprocal writing via a tailored optical far-field exposure, where the period of ripples varies along different scanning directions, and achieve a continuous manipulation of the period from 47 to 112 nm (±4 nm) for a 100-nm-thick indium tin oxide (ITO) on glass. A full electromagnetic model was developed to demonstrate the redistributed localized near-field at different stages of ablation with nanoscale precision. It explains the formation of ripples and the asymmetry of the focal spot determines the non-reciprocity of ripple writing. Combined with beam shaping techniques, we achieved non-reciprocal writing (regarding scanning direction) using an aperture-shaped beam. The non-reciprocal writing is expected to open new paths for precise and controllable nanoscale surface texturing.

Femtosecond laser upgrading the quality of bismuth films to enhance ultra-broadband photodetection

Topological insulator bismuth has attracted considerable attention for the fabrication of room-temperature, wide bandwidth, and high-performance photodetectors due to the gapless edge state and insulating bulk state properties. However, both the photoelectric conversion and carrier transportation of the bismuth films are extremely affected by the surface morphology and grain boundaries to limit optoelectronic properties further. Here, we demonstrate a strategy of femtosecond laser treatment for upgrading the quality of bismuth films. After the treatment with proper laser parameters, the measurement of average surface roughness can be reduced from Ra = 44 nm to 6.9 nm, especially with accompany of the evident grain boundary elimination. Consequently, the photoresponsivity of the bismuth films increases approximately 2 times within an ultra-broad spectrum range from the visible to mid-infrared. This investigation suggests that the femtosecond laser treatment can help to benefit the performance of topological insulator ultra-broadband photodetectors.

Laser-reduced graphene oxide for a flexible liquid sliding sensing surface

Flexible electronic skin is a flexible sensor system that imitates human skin. Recently, flexible sensors have been successfully developed. However, the droplet sliding sensing technology on a flexible electronic skin surface is still challenging. In this Letter, a flexible droplet sliding sensing surface is proposed and fabricated by laser-reduced graphene oxide (LRGO). The LRGO shows porous structures and low surface energy, which are beneficial for infusing lubricants and fabricating stable slippery surfaces. The slippery surface guarantees free sliding of droplets. The droplet sliding sensing mechanism is a combination of triboelectricity and electrostatic induction. After a NaCl droplet slides from lubricant-infused LRGO, a potential difference (∼0.2 mV) can be measured between two Ag electrodes. This study reveals considerable potential applications in intelligent robots and the medical field.

Laser Induced Coffee-Ring Structure through Solid-Liquid Transition for Color Printing

Metallic micro/nano structures with special physicochemical properties have undergone rapid development owing to their broad applications in micromachines and microdevices. Ultrafast laser processing is generally accepted as an effective technology for functional structures manufacture, however, the controllable fabrication of specific metallic micro/nano structures remains a challenge. Here, this work proposes a novel strategy of laser induced transient solid-liquid transition to fabricate unique structures. Through modulating the transient state of metal from solid to liquid phase using the initial pulse excitation, the subsequent ultrafast pulse-induced recoil pressure can suppress the plasma emission and removal of liquid phase metals, resulting in the controllable fabrication of coffee-ring structures. The solid-liquid transition dynamics, which related with the transient reflectivity and plasma intensity, are revealed by established two temperature model coupled with molecular dynamics model. The coffee-ring structure exhibits tunable structure color owing to various optical response, which can be used for color printing with large scale and high resolution. This work provides a promising strategy for fabricating functional micro/nano structures, which can greatly broaden the potential applications.

Quasicylindrical Waves for Ordered Nanostructuring

Laser-induced self-organization of periodic nanostructures on highly absorbing materials is widely understood to be due to interference between laser and surface plasmon polaritons (SPPs) that are excited by initial surface roughness. The structure order naturally emerges from the propagation phase of SPPs. Here, we reveal an unexplored mechanism that is predominantly induced by quasicylindrical waves (QCWs) with negligible contributions from SPPs. This mechanism features a new principle of order emergence in growth of periodic nanostructures through short-range electromagnetic interactions between QCWs and marginal nanofringes. In this scenario, the periodicity of nanostructures is not simply determined by the electromagnetic wavelength. With suppressed long-range interactions, the formation of nanostructures shows a domino-like growth process, thus significantly improving structure uniformity. An in situ microscopic observation is performed to characterize the temporal dynamics of structural growth and verify the new mechanism. Further, the QCWs are directly observed in experiments, which are theoretically supported by a scattering model.

Characteristics and aqueous dye removal ability of novel biosorbents derived from acidic and alkaline one-step ball milling of hickory wood

New classes of biosorbents are needed for various environment remediation applications. Thus, a facile and benign approach to synthesize porous biosorbents was developed using acidic or alkaline one-step ball milling of hickory wood biomass (AcBH and AlBH, respectively) without any external heat treatment, and their properties were compared. AcBH and AlBH were richer in O-containing functional groups, had enhanced porous structure and greater ability to remove crystal violet (CV, 476.4 mg g^-1) and Congo red (CR, 221.8 mg g^-1) dyes from aqueous solution, respectively, relative to hickory wood ball milled at neutral pH. Freundlich isotherm and pseudo second order kinetic models best fitted CR and CV adsorption onto biosorbents, indicating a mainly surface complexation adsorption mechanism. Further, both sorbents exhibited excellent stability and dye adsorption reusability. These results demonstrate that acidic and alkaline one-step ball milling is a facile and efficient approach for converting wood biomass into environmentally friendly biosorbents.

High damage threshold birefringent elements produced by ultrafast laser nanostructuring in silica glass

Birefringent patterning by ultrafast laser nanostructuring in silica glass has been used for space-variant birefringent optics with high durability and high optical damage threshold. We demonstrate that the oblate-shaped birefringent modification (type X) with ultrahigh optical transmission has higher optical damage resistance, comparable to pristine silica glass. The lower damage threshold of nanogratings based modification (type 2) following thermal annealing at 900°C for an hour is improved from 0.96 J/cm² to 1.62 J/cm² for 300 fs laser pulses and approaches the optical damage threshold of type X (1.56 J/cm²). This opens the door to utilize these optical elements for high power laser applications where optical transmission and damage threshold are the key parameters. The lower damage threshold of type 2 modification is related to the relatively high concentration of defects, such as E' centers and oxygen-deficiency centers (ODCs).

Self-Aligned Plasmonic Lithography for Maskless Fabrication of Large-Area Long-Range Ordered 2D Nanostructures

This paper proposes a one-step maskless 2D nanopatterning approach named self-aligned plasmonic lithography (SPL) by line-shaped ultrafast laser ablation under atmospheric conditions for the first time. Through a theoretical calculation of electric field and experimental verification, we proved that homogeneous interference of laser-excited surface plasmon polaritons (SPPs) can be achieved and used to generate long-range ordered 2D nanostructures in a self-aligned way over a wafer-sized area within several minutes. Moreover, the self-aligned nanostructures can be freely transferred between embossed nanopillars and engraved nanoholes by modulating the excitation intensity of SPPs interference through altering the incident laser energy. The SPL technique exhibits further controllability in the shape, orientation, and period of achievable nanopatterns on a wide range of semiconductors and metals by tuning processing parameters. Nanopatterned films can further act as masks to transfer structures into other bulk materials, as demonstrated in silica.

Femtosecond Laser Processing Technology for Anti-Reflection Surfaces of Hard Materials

The anti-reflection properties of hard material surfaces are of great significance in the fields of infrared imaging, optoelectronic devices, and aerospace. Femtosecond laser processing has drawn a lot of attentions in the field of optics as an innovative, efficient, and green micro-nano processing method. The anti-reflection surface prepared on hard materials by femtosecond laser processing technology has good anti-reflection properties under a broad spectrum with all angles, effectively suppresses reflection, and improves light transmittance/absorption. In this review, the recent advances on femtosecond laser processing of anti-reflection surfaces on hard materials are summarized. The principle of anti-reflection structure and the selection of anti-reflection materials in different applications are elaborated upon. Finally, the limitations and challenges of the current anti-reflection surface are discussed, and the future development trend of the anti-reflection surface are prospected.

Surface plasmons interference nanogratings: wafer-scale laser direct structuring in seconds

It is always a great challenge to bridge the nano- and macro-worlds in nanoscience, for instance, manufacturing uniform nanogratings on a whole wafer in seconds instead of hours even days. Here, we demonstrate a single-step while extremely high-throughput femtosecond laser scanning technique to obtain wafer-scale, highly regular nanogratings on semiconductor-on-metal thin films. Our technique takes advantage of long-range surface plasmons-laser interference, which is regulated by a self-initiated seed. By controlling the scanning speed, two types of nanogratings are readily manufactured, which are produced by either oxidation or ablation. We achieve a record manufacturing speed (>1 cm² s^-1), with tunable periodicity of Λ < 1 µm. The fractional variation of their periodicity is evaluated to be as low as ∆Λ/Λ ≈ 0.5%. Furthermore, by utilizing the semiconductor-on-metal film-endowed interference effects, an extremely high energy efficiency is achieved via suppressing light reflection during femtosecond laser nano-processing. As the fabricated nanogratings exhibit multi-functionality, we exemplify their practical applications in highly sensitive refractive index sensing, vivid structural colors, and durable superhydrophilicity.

Vivid Structural Color Macropatterns Created by Flexible Nanopainting of Ultrafast Lasers

Structural colors based on the macro- or nanostructure formation are ubiquitous in nature, having great prospects in many fields as a result of their environmentally friendly and long-term stable characteristics compared to pigments or dyes. However, the current fabrication techniques still face challenges for the generation of high-quality structural color patterns, especially at the macroscale, in an efficient way. Here, we demonstrate a method that exploits a flexible scanning process of generating macropatterns to convert the contour profiles into well-defined sub-micrometer grating structures with unprecedented vivid structural colors, at high speed and low cost on the graphene oxide film. The nature of dynamic beam shaping of the laser line spot allows us to flexibly construct the complex patterns at high speed, in sharp contrast to the traditional point-by-point laser processing. Moreover, the multicolor display of the patterns can be carried out by simply modulating the laser polarization to change the orientation of the sub-micrometer structures, and this nanopainting strategy is further explored to flexibly design the composite image for potential anti-counterfeiting applications.

Femtosecond laser plasmonic nano-printing metasurfaces for multiple-dimensional manipulation of light fields

Metasurfaces enable the multidimensional manipulation of light fields in a subwavelength scale. However, the low-cost preparation of large-area metasurfaces is still a challenge. In this Letter, we first, to the best of our knowledge, use the laser plasmonic nano-printing technique to efficiently manufacture metasurfaces with multidimensional manipulation capability. By utilizing a phase-polarization mapping method, we fabricated a silicon-based metasurface for color display, and indium tin oxide-based metasurfaces for decoupled near- and far-field holographic displays. This flexible and efficient laser plasmonic nano-printing method has great potential in the preparation of large-area metasurfaces, and is of great significance to promote the practical application of metasurfaces.

Electromagnetic origin of femtosecond laser-induced periodic surface structures on GaP crystals

The formations of different types of laser-induced periodic surface structures (LIPSS) on the surface of GaP crystals with different laser fluence are researched in experiments. The transition from the high spatial frequency LIPSS (HSFL) to the low spatial frequency LIPSS (LSFL) occurred as the number of the irradiated laser pulse increased. The finite difference time domain method combined with the holographic ablation model is used to simulate the LIPSS formation under the irradiation of multiple pulses. Different types of ripples are predicted by the electromagnetic approach. Results demonstrate that the electromagnetic origins of HSFL and LSFL are due to the interference of incident field and the scattering field under the multi-pulse irradiation.

Fabrication of Superhydrophobic Gully-Structured Surfaces by Femtosecond Laser and Imprinting for High-Efficiency Self-Cleaning Rain Collection

Freshwater is considered an essential need for humanity. Moreover, it is important to collect and make full use of rainwater. This work utilizes a femtosecond laser to fabricate micro-nanostructures on aluminum alloy substrates as molds. Then, the structures are imprinted on cheap and wildly used polypropylene (PP) materials. The just-imprinted PP surfaces with instinctive surface energy and replicated micro-nanostructures have an excellent superhydrophobic property with contact angles greater than 160° and anisotropic sliding angles smaller than 5° in parallel directions and smaller than 10° in the vertical directions. A small-scale rain collection device formed by a combination of the superhydrophobic PP surfaces is used to investigate the effects of the rain collection efficiency and total surface area relating to manufacturing cost. The rain collection device formed by the imprinted PP surfaces has high rain collection efficiency in terms of the volume of the collected water per square centimeter. For the light rain, the rain collection efficiency can reach an approximated maximum of 90%, more than 100% efficiency improvement of the device formed by flat PP surfaces in some cases. Therefore, the rain collection device is helpful in collecting water from rains in arid areas.

Graphene-based metasurface solar absorber design with absorption prediction using machine learning

Solar absorber is required to absorb most of the energy of the solar spectral irradiance. We propose a graphene-based solar absorber design with two different metasurfaces to improve this absorption and increase the efficiency of the solar absorber. The metasurfaces are selected based on their symmetrical/asymmetrical nature (O-shape and L-shape). The O-shape metasurface design is showing better performance over the L-shape metasurface design. The absorption performance is also compared with AM 1.5 solar spectral irradiance to show the effectiveness of the solar absorber. The absorption values are also enhanced by varying the parameters like resonator thickness and substrate thickness. The proposed solar absorber design gives maximum absorption in the ultraviolet and visible range. Furthermore, the design is also showing a high and similar absorption rate over a wide angle of incidence. The absorption of O-shape metasurface design is also predicted using machine learning. 1D-Convolutional Neural Network Regression is used to develop a Machine Learning model to determine absorption values of intermediate wavelength for assorted values of angle of incidence, resonator thickness, and substrate thickness. The results of experiments reveal that absorption values may be predicted with a high degree of accuracy. The proposed absorber with its high absorbing capacity can be applied for green energy applications.

Polarization-dependent Bloch oscillations in optical waveguides

Optical systems provide a new and practical platform for studying Bloch oscillations. This study investigates the fundamental-mode propagation of polarization-dependent Bloch oscillations. By using the three-dimensional properties of femtosecond laser direct writing, we fabricate a polymer-based gradient waveguide array and determine the Bloch oscillations under different polarization inputs by using the birefringence gradient and the equivalent refractive index, thus exhibiting a polarization-dependent Bloch period. Our results provide a new, to the best of our knowledge, paradigm for two-dimensional optical Bloch modes and highlight the influence of optical polarization in the same system, which provides a possibility to observe richer physics related to Bloch oscillations in one structure.

Micro-/Nano-Structures Fabricated by Laser Technologies for Optoelectronic Devices

Due to unique optical and electrical properties, micro-/nano-structures have become an essential part of optoelectronic devices. Here, we summarize the recent developments in micro-/nano-structures fabricated by laser technologies for optoelectronic devices. The fabrication of micro-/nano-structures by various laser technologies is reviewed. Micro-/nano-structures in optoelectronic devices for performance improvement are reviewed. In addition, typical optoelectronic devices with micro-nano structures are also summarized. Finally, the challenges and prospects are discussed.

Ten Open Questions about Laser-Induced Periodic Surface Structures

Laser-induced periodic surface structures (LIPSS) are a simple and robust route for the nanostructuring of solids that can create various surface functionalities featuring applications in optics, medicine, tribology, energy technologies, etc. While the current laser technologies already allow surface processing rates at the level of m2/min, industrial applications of LIPSS are sometimes hampered by the complex interplay between the nanoscale surface topography and the specific surface chemistry, as well as by limitations in controlling the processing of LIPSS and in the long-term stability of the created surface functions. This Perspective article aims to identify some open questions about LIPSS, discusses the pending technological limitations, and sketches the current state of theoretical modelling. Hereby, we intend to stimulate further research and developments in the field of LIPSS for overcoming these limitations and for supporting the transfer of the LIPSS technology into industry.

Electro-responsive actuators based on graphene

Electro-responsive actuators (ERAs) hold great promise for cutting-edge applications in e-skins, soft robots, unmanned flight, and in vivo surgery devices due to the advantages of fast response, precise control, programmable deformation, and the ease of integration with control circuits. Recently, considering the excellent physical/chemical/mechanical properties (e.g., high carrier mobility, strong mechanical strength, outstanding thermal conductivity, high specific surface area, flexibility, and transparency), graphene and its derivatives have emerged as an appealing material in developing ERAs. In this review, we have summarized the recent advances in graphene-based ERAs. Typical the working mechanisms of graphene ERAs have been introduced. Design principles and working performance of three typical types of graphene ERAs (e.g., electrostatic actuators, electrothermal actuators, and ionic actuators) have been comprehensively summarized. Besides, emerging applications of graphene ERAs, including artificial muscles, bionic robots, human-soft actuators interaction, and other smart devices, have been reviewed. At last, the current challenges and future perspectives of graphene ERAs are discussed.

Thermochemical Laser-Induced Periodic Surface Structures Formation by Femtosecond Laser on Hf Thin Films in Air and Vacuum

Thermochemical laser-induced periodic surface structures (TLIPSS) are a relatively new type of periodic structures formed in the focal area of linear polarized laser radiation by the thermally stimulated reaction of oxidation. The high regularity of the structures and the possibility of forming high-ordered structures over a large area open up possibilities for the practical application for changing the optical and physical properties of materials surface. Since the mechanism of formation of these structures is based on a chemical oxidation reaction, an intriguing question involves the influence of air pressure on the quality of structure formation. This paper presents the results on the TLIPSS formation on a thin hafnium film with fs IR laser radiation at various ambient air pressures from 4 Torr to 760 Torr. Despite the decrease in the oxygen content in the ambient environment by two orders of magnitude, the formation of high-ordered TLIPSS (dispersion in the LIPSS orientation angle δθ < 5°) with a period of ≈700 nm occurs within a wide range of parameters variation (laser power, scanning speed). This behavior of TLIPSS formation is in agreement with experimental data obtained earlier on the study of the kinetics of high-temperature oxidation of hafnium at various oxygen pressures.

Impact of Ultrashort Laser Nanostructuring on Friction Properties of AISI 314 LVC

Laser irradiation yields a powerful tool to modify the symmetry and asymmetry features of materials surfaces. In this paper, femtosecond laser-induced periodic surface structures were applied on stainless steel AISI 314, specially hardened by a low-vacuum carburizing procedure. Symmetry modifications in the surface’s morphology and chemistry before and after the laser treatment were investigated by SEM and EDS, respectively. Coefficient of friction (COF) was observed in dry sliding condition by using block-on-ring sliding test. The results show that COF values are substantially lower after laser-induced periodic surface structures (LIPSS) surface treatment.

Bioinspired Soft Robots Based on the Moisture-Responsive Graphene Oxide

Graphene oxide (GO), which has many oxygen functional groups, is a promising candidate for use in moisture-responsive sensors and actuators due to the strong water-GO interaction and the ultrafast transport of water molecules within the stacked GO sheets. In the last 5 years, moisture-responsive actuators based on GO have shown distinct advantages over other stimuli-responsive materials and devices. Particularly, inspired by nature organisms, various moisture-enabled soft robots have been successfully developed via rational assembly of the GO-based actuators. Herein, the milestones in the development of moisture-responsive soft robots based on GO are summarized. In addition, the working mechanisms, design principles, current achievement, and prospects are also comprehensively reviewed. In particular, the GO-based soft robots are at the forefront of the advancement of automatable smart devices.

Self-organized phase-transition lithography for all-inorganic photonic textures

Realizing general processing applicable to various materials by one basic tool has long been considered a distant dream. Fortunately, ultrafast laser-matter interaction has emerged as a highly universal platform with unprecedented optical phenomena and provided implementation paths for advanced manufacturing with novel functionalities. Here, we report the establishment of a three-dimensional (3D) focal-area interference field actively induced by a single ultrafast laser in transparent dielectrics. Relying on this, we demonstrate a radically new approach of self-organized phase-transition lithography (SOPTL) to achieve super-resolution construction of embedded all-inorganic photonic textures with extremely high efficiency. The generated textures exhibit a tunable photonic bandgap (PBG) in a wide range from ~1.3 to ~2 μm. More complicated interlaced textures with adjustable structural features can be fabricated within a few seconds, which is not attainable with any other conventional techniques. Evidence suggests that the SOPTL is extendable to more than one material system. This study augments light-matter interaction physics, offers a promising approach for constructing robust photonic devices, and opens up a new research direction in advanced lithography.

Engineering of gemcitabine coated nano-graphene oxide sheets for efficient near-infrared radiation mediated in vivo lung cancer photothermal therapy

Gemcitabine (GEM) and its derivatives of deoxycytosine is a promising anticancer candidate which is effective for the treatment of various cancers including lung cancer via cascade targetting Erk/Mek/Raf/Ras pathway and blocking the proliferation of the tumor cells. In this present work, we have described reduced graphene oxide (rGO) in the presence of anticancer utilizing ascorbic acid as reducing agents for lung cancer treatment. GEM reduced graphene oxide (termed as GEM-rGO) has resulted in a smooth and transparent morphological surface, which was confirmed by various spectroscopical investigations. The anticancer drug-loaded rGO has displayed remarkable cytotoxic activities against a panel of lung cancer cell lines when compared to the untreated lung cancer cells. Further, we examined the morphological observation of the cancer cell death was monitored through the fluorescence microscopic examinations. In addition, the cell deaths of the lung cancer cells were observed by the flow cytometry analyses. In addition, the non-toxic nature of potent GEM-rGO and GEM-rGO + NIR was confirmed by in vivo systemic toxicity analysis. Besides, the higher safety feature of the GEM-rGO and GEM-rGO + NIR was evidenced by histological analyses of the mice organs. The subcutaneous injection of GEM-rGO and GEM-rGO + NIR into mice bearing A549 xenografts more effectively inhibited the tumor than the free GEM. Based on the outcomes, we can summarise that the GEM reduced graphene oxide (GEM-rGO) can be used as a promising drug candidate for the treatment of lung cancer in the future.

Laser Synthesis and Microfabrication of Micro/Nanostructured Materials Toward Energy Conversion and Storage

Nanomaterials are known to exhibit a number of interesting physical and chemical properties for various applications, including energy conversion and storage, nanoscale electronics, sensors and actuators, photonics devices and even for biomedical purposes. In the past decade, laser as a synthetic technique and laser as a microfabrication technique facilitated nanomaterial preparation and nanostructure construction, including the laser processing-induced carbon and non-carbon nanomaterials, hierarchical structure construction, patterning, heteroatom doping, sputtering etching, and so on. The laser-induced nanomaterials and nanostructures have extended broad applications in electronic devices, such as light-thermal conversion, batteries, supercapacitors, sensor devices, actuators and electrocatalytic electrodes. Here, the recent developments in the laser synthesis of carbon-based and non-carbon-based nanomaterials are comprehensively summarized. An extensive overview on laser-enabled electronic devices for various applications is depicted. With the rapid progress made in the research on nanomaterial preparation through laser synthesis and laser microfabrication technologies, laser synthesis and microfabrication toward energy conversion and storage will undergo fast development.

Quo Vadis LIPSS?-Recent and Future Trends on Laser-Induced Periodic Surface Structures

Nanotechnology and lasers are among the most successful and active fields of research and technology that have boomed during the past two decades. Many improvements are based on the controlled manufacturing of nanostructures that enable tailored material functionalization for a wide range of industrial applications, electronics, medicine, etc., and have already found entry into our daily life. One appealing approach for manufacturing such nanostructures in a flexible, robust, rapid, and contactless one-step process is based on the generation of laser-induced periodic surface structures (LIPSS). This Perspective article analyzes the footprint of the research area of LIPSS on the basis of a detailed literature search, provides a brief overview on its current trends, describes the European funding strategies within the Horizon 2020 programme, and outlines promising future directions.

Bioinspired Surfaces With Switchable Wettability

The surface wettability of plants exhibits many unique advantages, which enhances the environmental adaptability of plants. In view of the rapid development of responsive materials, smart surfaces have been explored extensively to regulate surface wettability through external stimuli. Herein, we summarized recent advancements in bioinspired surfaces with switchable wettability. Typical bioinspired surfaces with switchable wettability and their emerging applications have been reviewed. In the end, we have discussed the remaining challenges and provided perspective on future development.

Scalable and High-Throughput Top-Down Manufacturing of Optical Metasurfaces

Metasurfaces have shown promising potential to miniaturize existing bulk optical components thanks to their extraordinary optical properties and ultra-thin, small, and lightweight footprints. However, the absence of proper manufacturing methods has been one of the main obstacles preventing the practical application of metasurfaces and commercialization. Although a variety of fabrication techniques have been used to produce optical metasurfaces, there are still no universal scalable and high-throughput manufacturing methods that meet the criteria for large-scale metasurfaces for device/product-level applications. The fundamentals and recent progress of the large area and high-throughput manufacturing methods are discussed with practical device applications. We systematically classify various top-down scalable patterning techniques for optical metasurfaces: firstly, optical and printing methods are categorized and then their conventional and unconventional (emerging/new) techniques are discussed in detail, respectively. In the end of each section, we also introduce the recent developments of metasurfaces realized by the corresponding fabrication methods.

Fabrication of a Z-scheme MoS2/CuO heterojunction for enhanced 2-mercaptobenzothiazole degradation activity and mechanism insight

A Z-scheme MoS₂/CuO photocatalyst is successfully developed using a hydrothermal and calcination method, which has excellent activity (96%) in the degradation of 2-mercaptobenzothiazole (MBT) under visible light irradiation.