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Memristors are regarded as one of the key devices to break through the traditional Von Neumann computer architecture due to their capability of simulating the function of neural synapses. Among various memristive materials, two-dimensional (2D) materials are promising candidates to build advanced memristors with extremely high integration density and low power consumption. However, memristors based on 2D materials usually suffer from poor endurance and retention due to their vulnerability to material degradation during the formation/fusing processes of conductive filament channels within the switching media of 2D materials. Here, a new memristor architecture based on a WS2/MoS2 2D semiconducting heterojunction (metal/heterojunction/metal, MHM) is proposed, which is completely different from the conventional metal/insulator/metal (MIM) sandwich structure. Through the introduction of a type-II 2D heterojunction, a resistance switching mechanism based on band modulation rather than the conductive filaments can be realized to eliminate the material degradation during the set/reset processes. A prototype MHM memristor based on the WS2/MoS2 heterojunction is successfully developed with a large switching on/off ratio up to 104 and a clearly extended endurance over 120 switching cycles, showing the advantage of the 2D WS2/MoS2 heterojunction over the individual MoS2 or WS2 layers in memristive performance. The proposed method for the MHM-type 2D memristor has the potential to achieve a large-scale integrated memristor matrix with low power consumption and high integration density, which is promising for future artificial intelligence and brain-like computing systems.

The widespread use of stimuli-responsive hydrogels is closely related to their synthesis efficiency. However, the widely used thermal-responsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels usually require a time-consuming synthesis process to produce (more than 12 h) and exhibit a relatively slow response speed in the field of cryo-polymerization. In this study, a sequence of thawing polymerization after freezing polymerization by a two-step method of free radical polymerization for the efficient synthesis of PNIPAM hydrogels (merely 2 h) with an excellent comprehensive performance is demonstrated. Results show that the overall performance of the as-synthesized PNIPAM hydrogels is at the top level among reported works despite the significantly reduced preparation time. Moreover, after incorporating multi-walled carbon nanotubes (MWNTs), the PNIPAM hydrogels exhibit a rapid near-infrared (NIR) light-response and programmable shape-morphing capability. It is believed that such a viable and time-saving synthetic method for producing PNIPAM hydrogels of high performance will lay a solid foundation for drug delivery and smart actuators.

A space channel design approach achieves dynamic meta-holography with high frame rate and large frame number., The hologram is an ideal method for displaying three-dimensional images visible to the naked eye. Metasurfaces consisting of subwavelength structures show great potential in light field manipulation, which is useful for overcoming the drawbacks of common computer-generated holography. However, there are long-existing challenges to achieving dynamic meta-holography in the visible range, such as low frame rate and low frame number. In this work, we demonstrate a design of meta-holography that can achieve 228 different holographic frames and an extremely high frame rate (9523 frames per second) in the visible range. The design is based on a space channel metasurface and a high-speed dynamic structured laser beam modulation module. The space channel consists of silicon nitride nanopillars with a high modulation efficiency. This method can satisfy the needs of a holographic display and be useful in other applications, such as laser fabrication, optical storage, optics communications, and information processing.

Laminated glass has a wide range of applications, but the cutting process is too cumbersome. In this paper, a novel laser composite separation method was proposed to separate the laminated glass by one time and simplify the cutting process from five steps to two steps for the first time by skillfully combining laser-induced thermal-crack propagation and laser thermal melting. This method generated three laser foci, and each laser focus is acting on one layer of laminated glass. Then, the composite mechanism combining laser-induced thermal-crack propagation for glass layers and laser thermal melting separation for PVB layer was realized to separate entire laminated glass. The experiments of separating laminated glass with thickness of 5 + 0.38 + 5 mm were carried out by laser composite separation successfully, and the separation side wall was very smooth (roughness of glass layer reached 10.24 nm) without any separation defects such as chipping, micro-cracks or subsurface damage. A mathematical model was also established to analyze the separation mechanism.

Thick glass is a widely used functional structure material, but the existing cutting methods are low quality, complex and time-consuming. In this paper, a flexible multi-focus laser separation technology (FMFLS) was developed to separate thick glass without pre-processing and follow-up polishing for the first time. The FMFLS adopted holed focusing lenses to generate multiple independent laser foci along glass thickness direction, which are beneficial to achieve optimal temperature and thermal stress distributions during separation. The positions and power densities of laser foci are flexible, which could be adjusted by changing the distances between focusing lenses to separate glass with different thickness and properties. By using FMFLS, a penetration crack could be formed and controlled easily by thermal stress to achieve safe and high-quality separation of glass. The FMFLS system was designed by optical analyzing and verified via experimental research. A numerical simulation analysis was also established to reveal the separating mechanism of FMFLS. A series of FMFLS experiments were carried out to separate the soda-lime and low-iron glass with thickness from 10 to 20 mm, which is 2–4 times thicker than that of traditional laser separating technologies. The results show that FMFLS can achieve a high-quality separation (roughness = 1.6 nm, scan length = 200 μm) of thick glass without any contamination, subsurface damage or edge breakage.

Due to excellent properties, Cr12MoV mold steel, 9Cr18 stainless steel and H13A cemented carbide are widely used in industry. In this paper, the effect of absorption of laser light on ablation efficiency and roughness have been studied using a picosecond pulse Nd:YVO4 laser. The experimental results reveal that laser wavelength, original surface roughness and chemical composition play an important role in controlling ablation efficiency and roughness. Firstly, higher ablation efficiency with lower surface roughness is achieved on the ablation of 9Cr18 at 532, comparing with 1064 nm. Secondly, the ablation efficiency increases while the Ra of the ablated region decreases with the decrease of original surface roughness on ablation of Cr12MoV mold steel at 532 nm. Thirdly, the ablation efficiency of H13A cemented carbide is much higher than 9Cr18 stainless steel and Cr12MoV mold steel at 1064 nm. Scanning electron microscopy images reveals the formation of pores on the surface of 9Cr18 stainless steel and Cr12MoV mold steel at 532 nm while no pores are formed at 1064 nm. As to H13A cemented carbide, worm-like structure is formed at 1064 nm. The synergetic effects of the heat accumulation, plasma shielding and ablation threshold on laser ablation efficiency and machining quality were analyzed and discussed systematically in this paper.

KDP crystal is an important electro-optic material in various laser systems, and belongs to very difficult-to-cut material, especially for thick crystals. In this study, an innovative separation method—laser multi-focus separation technology (LMFS) for thick KDP crystal has been developed by skillfully combining femtosecond laser and LMFS optical system of fiber laser for the first time. In this way, the uniformities of temperature and thermal stress distributions along crystal thickness and the utilization efficiency of the laser energy are greatly improved. A penetration crack along crystal thickness could be formed and its propagation direction could be controlled to achieve safe and high-quality separation. The separating thickness of LMFS (50 mm) is at least 4 times thicker than that of existing laser separating technologies, and the separating efficiency of LMFS (200 µm/s) is at least 20 times faster than that of traditional mechanical methods. The generation mechanism of multi-focus was expounded by optical analysis and design, and verified by an established LMFS optical system. A numerical simulation was also established to analyze the dynamic distributions of temperature and thermal stress of KDP crystal generated by the LMFS optical system, and explore the separation mechanism of LMFS. In addition, a window of appropriate processing parameters was predicted by a series of numerical simulations to successfully separate a thick KDP crystal with the thickness of 50 mm. The quality of the separated sidewall surface was clean and flat (roughness of 10.857 nm, flatness of 3.5389 µm) without any contamination, subsurface damage and edge fragmentation. The experimental results proved the feasibility of LMFS, and are in good agreement with the theoretical analysis.

In this paper, the effects of pulse repetition rate on ablation efficiency and quality of Cr12MoV cold work mold steel have been studied using a picosecond (ps) pulse Nd:YVO4 laser system at λ= 1064 nm. The experimental results of area ablation on target surface reveal that laser repetition rate plays a significant role in controlling ablation efficiency and quality. Increasing the laser repetition rate, while keeping a constant mean power improves the ablation efficiency and quality. For each laser mean power, there is an optimal repetition rate to achieve a higher laser ablation efficiency with low surface roughness. A high ablation efficiency of 42.29, 44.11 and 47.52 μm3/mJ, with surface roughness of 0.476, 0.463 and 0.706 μm could be achieved at laser repetition rate of 10 MHz, for laser mean power of 15, 17 and 19 W, respectively. Scanning electron microcopy images revels that the surface morphology evolves from rough with numerous craters, to flat without pores when we increased the laser repetition rate. The effects of laser repetition rate on the heat accumulation, plasma shield and ablation threshold were analyzed by numerical simulation, spectral analysis and multi-laser shot, respectively. The synergetic effects of laser repetition rate on laser ablation rate and machining quality were analyzed and discussed systemically in this paper.

Ultra-fast lasers can realize selective welding of glasses through nonlinear effect and have the advantages of having high welding accuracy, having small heat-affected zone, having high joint strength and not requiring intermediate absorption layer, which provides a new idea for chip packaging. However, this method is limited to the condition of optical contact, which is difficult to use in engineering applications. To solve this problem, an innovative seal welding method by picosecond laser is presented in this paper. In this method, a picosecond laser performs firstly rapid oscillating scan local welding of the two natural overlap glasses with a large contact gap to form a closed area consisting of spot welds. The glass contact gap in the closed area can be reduced to about 1.5 μm through the solidification shrinkage effect of spot welds. Then a good seal weld without plasma ablation, micro-hole, and micro-crack defects can be achieved by picosecond laser in this closed area to realize seal welding of glasses with a large contact gap. The sealing test results show that the seal welding samples can keep good sealing performance for more than one week.

Perovskite solar cells (PSCs) are a promising application industry, but its stability is not very ideal at present. The bottleneck of the PSCs industrialization is that perovskite material is very sensitive to humidity, and it is easy to produce hydrolysis and failure. Therefore, it is necessary to develop an effective encapsulation method to achieve a better long-term stability. Ultrashort pulse laser glass welding technology is one of the effective encapsulation methods, but it is still difficult to be used in engineering due to the harsh conditions of optical contact. To solve these problems, a sealing welding method of perovskite films based on ultrashort pulse laser under the natural stacking conditions was proposed, the effectiveness of the sealing weld was verified by experiments, which provides support for the engineering application of perovskite solar cells, and also provides a possible direction for the application of ultrashort pulse laser glass welding technology.

Cr12MoV has wide applications in the molds and dies industry. However, it is also a hard-to-machining material due to its high mechanical strength and hardness. Area ablation of Cr12MoV cold-work mold steel was carried out using a picosecond (ps) pulse Nd:YVO4 laser. The effects of laser fluence and wavelength on the ablation rate and machining quality were investigated with wavelengths of 1064 nm, 532 nm and 355 nm. The experimental results indicate a logarithmic increase of the ablation rate to a maximum value of ~41 nm/pulse with the increase of laser fluence using the wavelengths of 1064 nm and 355 nm. For the wavelength of 532 nm, an ablation rate of ~33 nm/pulse is achieved at low laser fluence of 8.28 J/cm2, then increases logarithmically into about 54 nm/pulse at 25.10 J/cm2, and then decreases steeply into almost zero as the laser fluence increases above 25.10 J/cm2. For the three laser wavelengths, different pore sizes were observed in the laser ablation region. The surface roughness increases exponentially with the increase of the laser fluence. The influence mechanisms of laser fluence and wavelength on the laser ablation rate and machining quality were systematically analyzed and discussed in this paper. Keywords: Ps-laser ablation, Cr12MoV, Ablation rate, Machining quality

International audience; Traditional metal interconnect technology faces several challenges when scaling down, such as electromigration and poisoning. Carbon nanotubes (CNTs) have been introduced in an attempt to solve these problems while providing on par performance. However, unexpected issues, such as great difficulty in manufacturing perfectly aligned CNTs and the undesired current leakage caused by electron percolation, still exist. In this work, we present novel vertically aligned CNT (VACNT)-based nanocomposites utilizing hexagonal boron nitride (h-BN) as intertube insulating/shielding layers that can be prepared in a scalable and controllable fashion. This composite material inherits the full advantages of the directional conductivity of VACNTs which are strongly enhanced by the intertube h-BN layer and demonstrate excellent electrical anisotropy. This composite material achieves conductivities of 1060.43 and 4.43 S m–1 along the directions parallel and perpendicular to the VACNTs, respectively, while the previously reported electrical conductivity of CNT–polymer and CNT–ceramic counterparts are well below 10–3 S m–1 isotropically. Because of its refractory ability, the h-BN layer can also protect the prepared nanocomposites from harsh oxidation and erosion, showing ultrahigh stability up to 1400 °C. These results reflect a giant step toward a simple, turnkey solution to an advanced CNT-based composite material for future electrical interconnect applications.

A dual laser beam separation technology (DLBS) for KDP crystal has been developed by skillfully combining femtosecond laser and continuous fiber laser. A clean crystal surface could be achieved by DLBS.

KDP crystal is an important electro-optic material in various laser systems. At present, the greatest difficulty is the cutting and polishing of large-scale crystals. In this study, a laser nondestructive mirror-separation technology (LNMS) for KDP crystal has been developed for the first time by skillfully adopting femtosecond laser pretreating and fiber laser separating. The separating efficiency of LNMS is at least 200 times faster than that of traditional mechanical cutting, and a nondestructive mirror-separated crystal sidewall with surface roughness (Sa) of 4.7 nm (P−V) and 2.1 nm (RMS), flatness of 5.433 μm and an angular precision about 0.06° could be obtained using the LNMS method. The effects of laser separating parameters, including laser power, laser moving speed and internal stress release on separating accuracy and quality, were investigated and optimized; meanwhile its principle was expounded as well as its mechanism was discussed. The experimental and analyzed results show that the LNMS technology may also have a prospect in the analysis of residual stress distribution inside KDP crystal. A numerical simulation on the thermal stress in the LNMS separating process of KDP crystal was developed to analyze the separating mechanism, which is in good agreement with the theoretical analysis and experimental results.

International audience; Traditional ceramic-based, high-temperature electrode materials (e.g., lanthanum chromate) are severely limited due to their conditional electrical conductivity and poor stability under harsh circumstances. Advanced composite structures based on vertically aligned carbon nanotubes (VACNTs) and high-temperature ceramics are expected to address this grand challenge, in which ceramic serves as a shielding layer protecting the VACNTs from the oxidation and erosive environment, while the VACNTs work as a conductor. However, it is still a great challenge to fabricate VACNT/ceramic composite structures due to the limited diffusion of ceramics inside the VACNT arrays. In this work, we report on the controllable fabrication of infiltrated (and noninfiltrated) VACNT/silicon composite structures via thermal chemical vapor deposition (CVD) [and laser-assisted CVD]. In laser-assisted CVD, low-crystalline silicon (Si) was quickly deposited at the VACNT subsurfaces/surfaces followed by the formation of high-crystalline Si layers, thus resulting in noninfiltrated composite structures. Unlike laser-assisted CVD, thermal CVD activated the precursors inside and outside the VACNTs simultaneously, which realized uniform infiltrated VACNT/Si composite structures. The growth mechanisms for infiltrated and noninfiltrated VACNT/ceramic composites, which we attributed to the different temperature distributions and gas diffusion mechanism in VACNTs, were investigated. More importantly, the as-farbicated composite structures exhibited excellent multifunctional properties, such as excellent antioxidative ability (up to 1100 °C), high thermal stability (up to 1400 °C), good high velocity hot gas erosion resistance, and good electrical conductivity (∼8.95 Sm–1 at 823 K). The work presented here brings a simple, new approach to the fabrication of advanced composite structures for hot electrode applications.

Laser shock peening using low-energy nanosecond (ns) fiber lasers was investigated in this study to realize high-speed micro-scale laser shock peening on selected positions without causing surface damage. Due to the employment of a fiber laser with high-frequency and prominent environmental adaptability, the laser peening system is able to work with a much higher speed compared to traditional peening systems using Nd:YAG lasers and is promising for in-situ applications in harsh environments. Detailed surface morphology investigations both on sacrificial coatings and Al alloy surfaces after the fiber laser peening revealed the effects of focal position, pulse duration, peak power density, and impact times. Micro-dent arrays were also obtained with different spot-to-spot distances. Obvious micro-hardness improvement was observed inside the laser-peening-induced microdents after the fiber laser shock peening.

Laser shock micro-forming is a non-thermal laser forming method that uses laser-induced shockwave to modify surface properties and to adjust shapes and geometry of work pieces. The magnitude and spatial distribution of the laser-induced shockwaves depend on the energy profiles of the laser beam focused on sample surfaces. In this paper, we present an adaptive optical technique to engineer spatial profiles of laser beams to control the shapes, sizes, and locations of the laser-induced shockwaves and the resulting forming features. Using a spatial light modulator, this adaptive laser beam forming tool was used to process free-standing MEMS structures in aluminum, which has led to highly uniform forming features. Shockwave simultaneously excited by multiple laser beams generated by the spatial light modulator and its effects on the micro-forming process were also studied. The results presented in this paper show that the adaptive optics laser beam forming is an effective and flexible method to generate shockwave with various shapes and sizes of wavefront and at multiple locations for laser processing at microscales.

In this study, long-range ordered straight holes with definable open pattern and diameter of 100–200 μm were manufactured using a 355 nm Nd:YVO 4 ultraviolet laser to sustain Nafion resin for durable proton exchange membranes. Composite proton exchange membrane prepared from the straight-hole polyimide support successfully reduced the dimensional swelling and humidity-induced stress of the proton exchange membrane under variable humidities. The effect of laser fluence and overlap rate on the size precision and quality of the straight holes were investigated. The thermodynamic mechanical capacity of composite proton exchange membrane and the single cell performance were also determined. The experimental results showed that long-range ordered straight holes with high precision and good quality could be achieved by laser trepanning with appropriate scanning speed, high repetition frequency and suitable laser fluence.

KDP crystal is an important optic-electro material in various laser systems, at present, the greatest difficulty is the cutting of large-scale crystals. In this study, a dual laser beam separation technology (DLBS) for KDP crystal has been developed by skillfully combining femtosecond laser and continuous fiber laser for the first time. The principle of DLBS is expounded. The effects of laser separating parameters, including laser output power, scanning speed, focal position and focal length on separating accuracy and quality (flatness and surface roughness Sa of the separated sidewall) were investigated. The key parameters were determined and optimized for the separating of raw materials with the minimal flatness and the separating of the end product crystals with minimal Sa. The results show that a clean crystal surface and an average Sa of 2.6843 μm separated sidewall without any pollution, subsurface damage and limbic fragmentation could be achieved by DLBS. The separating speed of DLBS is at least 20 times faster than that of the conventional method. A numerical simulation to analyze the mechanism of DLBS separating KDP crystal was developed, which is in good agreement with the theoretical analysis and experimental results.

The transmission properties of a focused laser inside anisotropic material are complex due to the birefringent effect, which has remarkable influence on the light distribution and frequency multiplication efficiency of crystals. Meanwhile, it will also affect the laser micromachining precision of birefringent materials with random polarization. In this study, ray tracing and diffraction integral methods were proposed to develop the mathematical model of a laser focused through an isotropic medium into a KDP crystal. Using these models, the focusing properties and 3D light intensity distribution of a focused laser inside a KDP crystal at different orientations were investigated. The research shows that the size and shape of the E-ray focus will distort, and its peak power density decreases rapidly with the decrease of the angle between the optical axis and the crystal surface. Meanwhile, the focal position of the E-ray will also move with the change of optical axis orientation. Based on the simulated results, an approximate 3D light intensity equation of a laser focused into birefringent material was also proposed, which is in good agreement with the theoretical analysis. The related simulated results have an important engineering value for nonlinear optics and laser processing of birefringent materials.

Laser processing 3-D microstructures inside KDP crystals is an effective way to suppress the transverse stimulated ramam scattering（TSRS）in high power lasers. A simulation study on the transmission characteristics of focused laser inside KDP crystal was carried out to investigate the feasibility of laser processing 3-D microstructures and the effects of laser parameters on the machining accuracy, efficiency and yield. The effects of the peak power density, spot distortion and deviation of laser focus are the main factors on the machining accuracy and crystal fragmentation. The size and shape of the e-ray focus will distort and its peak power density decreases rapidly with the increasing of angle between incident laser and crystal optical axis. The results show that the effect of the e-ray will make the processing efficiency increase more than double when the angle is less than 15°, and can be neglected in the low-energy or easily causes crystal fragmentation in high-energy when the angle is greater than 30°, in this case the e-ray should be shielded. The related simulated results have an important engineering value on increasing the accuracy of laser micromachining birefringent materials.

A simulation study on the transmission characteristics of focused laser inside KDP crystal was carried out to investigate the effects of laser parameters on the micromachining accuracy, efficiency and quality for laser processing 3-D microstructures.