Onion-structured transition metal dichalcogenide nanoparticles by laser fabrication in liquids and atmospheres

Since the discovery of transition metal dichalcogenide(TMDC)nanoparticles(NPs)with the onion-like structure,many efforts have been made to develop their fabrication methods.Laser fabrication(LF)is one of the most promising methods to prepare onion-structured TMDC(or OS-TMDC)NPs due to its green,flexible,and scalable syntheses.In this mini-review article,we systematically introduce various laser-induced OS-TMDC(especially the OS-MoS_(2))NPs,their formation mechanism,properties,and applications.The preparation routes mainly include laser ablation in liquids and atmospheres,and laser irradiation in liquids.The various formation mechanisms are then introduced based on the different preparation routes,to describe the formations of the corresponding OS-NPs.Finally,some interesting properties and novel applications of these NPs are briefly demonstrated,and a short outlook is also given.This review could help to understand the progress of the laser-induced OS-TMDC NPs and their applications.

Holographic laser fabrication of 3D artificial compound μ-eyes

The demand for fast optical image acquisition without movable optical elements(e.g.,for self-driving car technology)can be met using bioinspired 3D compound eyes.3D laser processing strategies enable designable 3D structuring but suffer from low fabrication efficiency,which significantly limits their applications in producing complex 3D optical devices.Herein,we demonstrate a versatile yet simple wet-etching-assisted holographic laser fabrication method for the development of 3D compound eyes.Artificial compoundμ-eyes can be readily fabricated by programming a 3D spot array for the parallel ablation of a curved fused silica surface,followed by controllable etching in a hydrofluoric(HF)acid solution.A 3D-concave-lens array made on a curved surface over an area of 100μm cross-section with each lenslet of 10μm radius was fabricated with high fidelity and excellent imaging/focusing quality.The resultant 3D-concave-lens can serve as a hard template for the mass production of soft compound eyes through soft lithography.Additionally,using a generative adversarial network(GAN)-based deep learning algorithm,image restoration was conducted for each lenslet,which retained a large field of view and significantly improved image quality.This method provides a simple solution to the requirements of compoundμ-eyes required by Industry 4.0.

Self-propelled Leidenfrost droplets on femtosecond-laser-induced surface with periodic hydrophobicity gradient

The controllable transfer of droplets on the surface of objects has a wide application prospect in the fields of microfluidic devices,fog collection and so on.The Leidenfrost effect can be utilized to significantly reduce motion resistance.However,the use of 3D structures limits the widespread application of self-propulsion based on Leidenfrost droplets in microelectromechanical system.To manipulate Leidenfrost droplets,it is necessary to create 2D or quasi-2D geometries.In this study,femtosecond laser is applied to fabricate a surface with periodic hydrophobicity gradient(SPHG),enabling directional self-propulsion of Leidenfrost droplets.Flow field analysis within the Leidenfrost droplets reveals that the vapor layer between the droplets and the hot surface can be modulated by the SPHG,resulting in directional propulsion of the inner gas.The viscous force between the gas and liquid then drives the droplet to move.

Laser fabrication of graphene-based supercapacitors

Supercapacitors(SCs)have broad applications in wearable electronics(e.g.,e-skin,robots).Recently,graphenebased supercapacitors(G-SCs)have attracted extensive attention for their excellent flexibility and electrochemical performance.Laser fabrication of G-SCs exhibits obvious superiority because of the simple procedures and integration compatibility with future electronics.Here,we comprehensively summarize the state-of-the-art advancements in laser-assisted preparation of G-SCs,including working mechanisms,fabrication procedures,and unique characteristics.In the working mechanism section,electric double-layer capacitors and pseudocapacitors are introduced.The latest advancements in this field are comprehensively summarized,including laser reduction of graphene oxides,laser treatment of graphene prepared from chemical vapor deposition,and laserinduced graphene.In addition,the unique characteristics of laser-enabled G-SCs,such as structured graphene,graphene hybrids,and heteroatom doping graphene-related electrodes,are presented.Subsequently,laser-enabled miniaturized,stretchable,and integrated G-SCs are also discussed.It is anticipated that laser fabrication of G-SCs holds great promise for developing future energy storage devices.

two-dimensional material functional devices enabled by direct laser fabrication

During the past decades,atomically thin,two-dimensional（2D）layered materials have attracted tremen-dous research interest on both fundamental properties and practical applications because of their extraordinary mechanical,thermal,electrical and optical properties,which are distinct from their counterparts in the bulk format.Various fabrication methods,such as soft-lithography,screen-printing,colloidal-templating and chemical/dry etching have been developed to fabricate micro/ nanostructures in 2D materials.Direct laser fabrication with the advantages of unique three-dimensional（3D）processing capability,arbitrary-shape designability and high fabrication accuracy up to tens of nanometers,which is far beyond the optical diffraction limit,has been widely studied and applied in the fabrication of various micro/ nanostructures of 2D materials for functional devices.This timely review summarizes the laser-matter interaction on 2D materials and the significant advances on laser-assisted 2D materials fabrication toward diverse functional photonics,optoelectronics,and electrochemical energy storage devices.The perspectives and challenges in designing and improving laser fabricated 2D materials devices are discussed as well.

Ablation enhancement by defocused irradiation assisted femtosecond laser fabrication of stainless alloy

We evaluate the effects of the holes geometry drilled by a femtosecond laser on a stainless alloy with various defocused irradiation time, which ranges from 0 min to 1 h. The laser ablation efficiency is increased by a factor of3 when the irradiation time is elevated from 0 to 30 min. Also, the morphology of the hole is observed by a scanning electron microscope, where the result indicates that the defocused irradiation time has a significant influence on the morphology changes. The reason for such changes is discussed based on the pretreatment effect and the confined plasma plume. As an application example, the microchannel is fabricated by a femtosecond laser combined with the defocused irradiation to demonstrate the advantage of the proposed method in fabricating functional structures.

Fabrication of Through Micro-hole Arrays in Silicon Using Femtosecond Laser Irradiation and Selective Chemical Etching

We demonstrate a method of fabricating through micro-holes and micro-hole arrays in silicon using femtosecond laser irradiation and selective chemical etching. The micro-hole formation mechanism is identified as the chemical reaction of the femtosecond laser-induced structure change zone and hydrofluoric acid solution. The morphologies of the through micro-holes and micro-hole arrays are characterized by using scanning electronic microscopy, The effects of the pulse number on the depth and diameter of the holes are investigated. Honeycomb arrays of through micro-holes fabricated at different laser powers and pulse numbers are demonstrated.

Photonic crystal fiber Mach-Zehnder interferometer with microholes ablated by a femtosecond laser for refractive index sensing

A new structure of the photonic crystal fiber（PCF）based Mach-Zednder interferometer（MZI）is fabricated and presented.The structure has microholes ablated by a femtosecond laser.The fringe visibility can be enhanced more than 10 dB compared with the interferometer without a microhole.The interferometer is characterized by sodium chloride solutions for refractive index（RI）sensing.The RI sensitivities are greatly increased by the hole fabrication since it directly changes the cladding modes of the PCF.For the interferometer sensor with two holes,the RI sensitivity is 157.74 nm/RIU,which is 5 times than that of the sensor without a microhole.Microholes ablation with a femtosecond laser on PCF can increase the sensor＇s sensitivity dramatically.Femtosecond laser has a wide application prospect in the field of performance improvement of the sensors.

Ultrashort pulsed laser induced complex surface structures generated by tailoring the melt hydrodynamics

We present a novel approach for tailoring the laser induced surface topography upon femtosecond(fs)pulsed laser irradiation.The method employs spatially controlled double fs laser pulses to actively regulate the hydrodynamic microfluidic motion of the melted layer that gives rise to the structures formation.The pulse train used,in particular,consists of a previously unexplored spatiotemporal intensity combination including one pulse with Gaussian and another with periodically modulated intensity distribution created by Direct Laser Interference Patterning(DLIP).The interpulse delay is appropriately chosen to reveal the contribution of the microfluidic melt flow,while it is found that the sequence of the Gaussian and DLIP pulses remarkably influences the surface profile attained.Results also demonstrate that both the spatial intensity of the double pulse and the effective number of pulses per irradiation spot can further be modulated to control the formation of complex surface morphologies.The underlying physical processes behind the complex patterns’generation were interpreted in terms of a multiscale model combining electron excitation with melt hydrodynamics.We believe that this work can constitute a significant step forward towards producing laser induced surface structures on demand by tailoring the melt microfluidic phenomena.

Carnivorous plants inspired shape-morphing slippery surfaces

Carnivorous plants,for instance,Dionaea muscipula and Nepenthes pitcher plant,inspired the innovation of advanced stimuli-responsive actuators and lubricant-infused slippery surfaces,respectively.However,hybrid bionic devices that combine the active and passive prey trapping capabilities of the two kinds of carnivorous plants remain a challenge.Herein,we report a moisture responsive shape-morphing slippery surface that enables both moisture responsive shapemorphing and oil-lubricated water repellency for simultaneous active-and passive-droplet manipulation.The moisture deformable slippery surface is prepared by creating biomimetic microstructures on graphene oxide(GO)membrane via femtosecond laser direct writing and subsequent lubricating with a thin layer of oil on the laser structured reduced GO(LRGO)surface.The integration of a lubricant-infused slippery surface with an LRGO/GO bilayer actuator endows the actuator with droplet sliding ability and promotes the moisture deformation performance due to oil-enhanced water repellency of the inert layer(LRGO).Based on the shape-morphing slippery surface,we prepared a series of proof-of-concept actuators,including a moisture-response Dionaea muscipula actuator,a smart frog tongue,and a smart flower,demonstrating their versatility for active/passive trapping,droplet manipulation,and sensing.

Pattern recognition in multi-synaptic photonic spiking neural networks based on a DFB-SA chip

Spiking neural networks(SNNs)utilize brain-like spatiotemporal spike encoding for simulating brain functions.Photonic SNN offers an ultrahigh speed and power efficiency platform for implementing high-performance neuromorphic computing.Here,we proposed a multi-synaptic photonic SNN,combining the modified remote supervised learning with delayweight co-training to achieve pattern classification.The impact of multi-synaptic connections and the robustness of the network were investigated through numerical simulations.In addition,the collaborative computing of algorithm and hardware was demonstrated based on a fabricated integrated distributed feedback laser with a saturable absorber(DFB-SA),where 10 different noisy digital patterns were successfully classified.A functional photonic SNN that far exceeds the scale limit of hardware integration was achieved based on time-division multiplexing,demonstrating the capability of hardware-algorithm co-computation.

Diffusion dynamics and characterization of attogram masses in optically trapped single nanoparticles using laser-induced plasma imaging

In the present work,a wavelength-selected plasma imaging analysis system is presented and used to track photons emitted from single-trapped nanoparticles in air at atmospheric pressure.The isolated nanoentities were atomized and excited into plasma state using single nanosecond laser pulses.The use of appropriate wavelength filters alongside time-optimized acquisition settings enabled the detection of molecular and atomic emissions in the plasma.The photon detection efficiency of the imaging line resulted in a signal>400 times larger than the simultaneously-acquired dispersive spectroscopy data.The increase in sensitivity outlined the evolution of diverse physicochemical processes at the single particle scale which included heat and momentum transfer from the plasma into the particle as wells as chemical reactions.The imaging detection of excited fragments evidenced different diffusion kinetics and time frames for atoms and molecules and their influence upon both the spectroscopic emission readout and fabrication processes using the plasma as a reactor.Moreover,the origin of molecular species,whether naturally-occurring or derived from a chemical reaction in the plasma,could also be studied on the basis of compositional gradients found on the images.Limits of detection for the inspected species ranged from tens to hundreds attograms,thus leading to an exceptional sensing principle for single nanoentities that may impact several areas of science and technology.

Fabrication of EAM-Integrated DFB Lasers With A Coupling Waveguide

EAM-DFB monolithic light sources with the coupling waveguide between laser and modulator have been developed. 10mw output light power at 90mA and 18dB extinction ratio at -2V has been achieved.

Anisotropic dewetting polydimethylsiloxane surface fabricated using ultrashort laser pulses

Anisotropic dewetting polydimethylsiloxane （PDMS） surfaces, which consist of groove-like micro/ nanostructures （so-called hierarchical structures）, are fabricated using an ultrashort pulsed laser. The contact angles （CAs） are measured parallel to the microgrooves, which are always larger than those measured perpendicular to the microgrooves, exhibiting a superhydrophobic anisotropy of approximately 4°on these fabricated PDMS surfaces at optimized parameters. These pulsed-laser irradiated surfaces exhibit enhanced hydrophobicity with CAs that increase from 116°to 156°while preserving the anisotropic dewetting. Additionally, the wettability of the surfaces with different morphologies is investigated. The temporal evolution of the wettability of the pulsed-laser irradiated PDMS surface is also observed within the first few hours after pulsed laser irradiation.

Effect of Scanning Beam Profile to Fabricate Fused Fiber Tapers by CO_2 Laser Irradiation Method

Beam uniformity is a crucial building block of CO2 experiments aimed at fusing and stretching optical fibers in a lossless manner. When the irradiation beam is expanded through a galvanometer mirror, ways to achieve beam uniformity are investigated.