3D Nanoprinting of Heterogeneous Metal Oxides with High Shape Fidelity.

3D nanoprinting can significantly enhance the performance of sensors, batteries, optoelectronic/microelectronic devices, etc. However, current 3D nanoprinting methods for metal oxides are suffering from three key issues including limited material applicability, serious shape distortion, and the difficulty of heterogeneous integration. This paper discovers a mechanism in which imidazole and acrylic acid synergistically coordinate with metal ions in water. Using the mechanism, this work develops a series of metal ion synergistic coordination water-soluble (MISCWS) resins for 3D nanoprinting of various metal oxides, including MnO2, Cr2O3, Co3O4, and ZnO, as well as heterogeneous structures of MnO2/NiO, Cr2O3/Al2O3, and ZnO/MgO. Besides, the synergistic coordination effect results in a 2.54-fold increase in inorganic mass fraction within the polymer, compared with previous works, which effectively mitigates the shape distortion of metal oxide microstructures. Based on this method, this work also demonstrates a 3D ZnO microsensor with a high sensitivity (1.113 million at 200 ppm NO2), surpassing the conventional 2D ZnO sensors by tenfold. The method yields high-fidelity 3D structures of heterogeneous metal oxides with nanoscale resolution, paving the way for applications such as sensing, micro-optics, energy storage, and microsystems.

3D Directional Assembly of Liquid Crystal Molecules.

The precise construction of hierarchically long-range ordered structures using molecules as fundamental building blocks can fully harness their anisotropy and potential. However, the 3D, high-precision, and single-step directional assembly of molecules is a long-pending challenge. Here, a 3D directional molecular assembly strategy via femtosecond laser direct writing (FsLDW) is proposed and the feasibility of this approach using liquid crystal (LC) molecules as an illustrative example is demonstrated. The physical mechanism for femtosecond (fs) laser-induced assembly of LC molecules is investigated, and precise 3D arbitrary assembly of LC molecules is achieved by defining the discretized laser scanning pathway. Additionally, an LC-based Fresnel zone plate array with polarization selection and colorization imaging functions is fabricated to further illustrate the potential of this method. This study not only introduces a 3D high-resolution alignment method for LC-based functional devices but also establishes a universal protocol for the precise 3D directional assembly of anisotropic molecules.

Study on Laser-Electrochemical Hybrid Polishing of Selective Laser Melted 316L Stainless Steel.

The process of forming metal components through selective laser melting (SLM) results in inherent spherical effects, powder adhesion, and step effects, which collectively lead to surface roughness in stainless steel, limiting its potential for high-end applications. This study utilizes a laser-electrochemical hybrid process to polish SLM-formed 316L stainless steel (SS) and examines the influence of process parameters such as laser power and scanning speed on surface roughness and micro-morphology. A comparative analysis of the surface roughness, microstructure, and wear resistance of SLM-formed 316L SS polished using laser, electrochemical, and laser-electrochemical hybrid processes is presented. The findings demonstrate that, compared to laser and electrochemical polishing alone, the laser-electrochemical hybrid polishing exhibits the most significant improvement in surface roughness and the highest material wear resistance. Additionally, the hybrid process results in a surface free of cracks and only a small number of tiny corrosion holes, making it more suitable for polishing the surface of 316L SS parts manufactured via SLM.

High-quality and efficient large-area copper removal utilizing laser-induced active mechanical peeling.

Large-area copper layer removal is one of the essential processes in manufacturing printed circuit boards (PCB) and frequency selective surfaces (FSS). However, laser direct ablation (LDA) with one-step scanning is challenging in resolving excessive substrate damage and material residue. Here, this study proposes a laser scanning strategy based on the laser-induced active mechanical peeling (LIAMP) effect generated by resin decomposition. This scanning strategy allows the removal of large-area copper layers from FR-4 copper-clad laminates (FR-4 CCL) in one-step scanning without additional manual intervention. During the removal process, the resin decomposition in the laser-irradiated area provides the mechanical tearing force, while the resin decomposition in the laser-unirradiated area reduces the interfacial adhesion force and provides recoil pressure. By optimizing scanning parameters to control the laser energy deposition, the substrate damage and copper residue can be effectively avoided. In our work, the maximum removal efficiency with different energy densities, pulse duration, and repetition frequency are 31.8 mm2/ms, 30.25 mm2/ms, and 82.8 mm2/ms, respectively. Compared with the reported copper removal using laser direct write lithography technology combined with wet chemical etching (LDWL+WCE) and LDA, the efficiency improved by 8.3 times and 66 times. Predictably, the laser scanning strategy and the peeling mechanism are simple and controllable, which have potential in electronics, communications, and aerospace.

Extending the 3D scanning range of reflective dynamic focusing device-based laser scanners.

Reflective dynamic focusing devices (RDFDs) have shown their potential in laser scanning as high-performance laser Z-direction focusing devices. However, the scanning range of RDFD-based scanners is limited by aberrations during dynamic focusing. An aspheric symmetry correction (ASC) method was proposed to extend the effective scanning range. An aspheric lens was introduced to correct the optical path difference (OPD) and optimize aberrations. As a result, the scanning range in the three-dimensional (3D) space increased by 15.2%. The ASC method has been proven to extend the 3D scanning range of RDFD-based scanners and may have broad application prospects.

Insight into the surface behavior and dynamic absorptivity of laser removal of multilayer materials.

Laser-materials interaction is the fascinating nexus where laser optics, physical/ chemistry, and materials science intersect. Exploring the dynamic interaction process and mechanism of laser pulses with materials is of great significance for analyzing laser processing. Laser micro/nano processing of multilayer materials is not an invariable state, but rather a dynamic reaction with unbalanced and multi-scale, which involves multiple physical states including laser ablation, heat accumulation and conduction, plasma excitation and shielding evolution. Among them, several physical characteristics interact and couple with each other, including the surface micromorphology of the ablated material, laser absorption characteristics, substrate temperature, and plasma shielding effects. In this paper, we propose an in-situ monitoring system for laser scanning processing with coaxial spectral detection, online monitoring and identification of the characteristic spectral signals of multilayer heterogeneous materials during repeated scanning removal by laser-induced breakdown spectroscopy. Additionally, we have developed an equivalent roughness model to quantitatively analyze the influence of surface morphology changes on laser absorptivity. The influence of substrate temperature on material electrical conductivity and laser absorptivity was calculated theoretically. This reveals the physical mechanism of dynamic variations in laser absorptivity caused by changes in plasma characteristics, surface roughness, and substrate temperature, and it provides valuable guidance for understanding the dynamic process and interaction mechanism of laser with multilayer materials.

Drop Impact on Submillimeter-Structured Surfaces with Different Wetting Behaviors.

Droplet impact behaviors are crucial in controlling infectious diseases, inkjet printing, and anti-icing applications. The wettability and microstructure of the material surface are critical factors in this regard. Compared to microstructures, submillimeter structures are more damage-resistant, thereby ensuring droplet impact behaviors' stability. Herein, submillimeter-structured PDMS surfaces with varying wetting properties were prepared to investigate droplet impact behaviors. Experimental results indicate that submillimeter-structured surfaces are more prone to droplet splashing than flat surfaces, which can be suppressed by increasing surface hydrophilicity. An increase in the submillimeter pillar height and a decrease in spacing result in an increased critical Weber number. Additionally, the capillary forces of the superhydrophilic surface lead to droplet impact, accompanied by deposition. This study supports the long-term stable use of the droplet impact effect to achieve fluid separation.

Laser adaptive processing technology for multilayer dissimilar materials.

We report a laser adaptive processing technology (LAPT) for the selective removal of Cu/Al multilayer dissimilar materials. Using the wavelength range and intensity distribution of the characteristic spectrum, the properties and content of multilayer dissimilar materials can be analyzed online based on laser-induced breakdown spectroscopy. The traditional low-speed spectral detection mode was transformed into a high-speed photoelectric detection method by using a scheme consisting of a bandpass filter with an avalanche photodetector (APD), and the in situ online detection of a 30 ns, 40 kHz high-frequency pulse signal during laser scanning was realized. Combined with a field programmable gate array (FPGA) digital control unit, online feedback and closed-loop control were achieved at the kHz level, and the adaptive intelligent control of material interfaces and laser processing parameters was achieved. This excellently demonstrated the feasibility and flexibility of LAPT for processing arbitrary multilayer dissimilar materials.

Laser Powder Bed Fusion of 316L Stainless Steel: Effect of Laser Polishing on the Surface Morphology and Corrosion Behavior.

Recently, laser polishing, as an effective post-treatment technology for metal parts fabricated by laser powder bed fusion (LPBF), has received much attention. In this paper, LPBF-ed 316L stainless steel samples were polished by three different types of lasers. The effect of laser pulse width on surface morphology and corrosion resistance was investigated. The experimental results show that, compared to the nanosecond (NS) and femtosecond (FS) lasers, the surface material's sufficient remelting realized by the continuous wave (CW) laser results in a significant improvement in roughness. The surface hardness is increased and the corrosion resistance is the best. The microcracks on the NS laser-polished surface lead to a decrease in the microhardness and corrosion resistance. The FS laser does not significantly improve surface roughness. The ultrafast laser-induced micro-nanostructures increase the contact area of the electrochemical reaction, resulting in a decrease in corrosion resistance.

Non-uniform droplet deposition on femtosecond laser patterned superhydrophobic/superhydrophilic SERS substrates for high-sensitive detection.

Surface-enhanced Raman scattering (SERS) sensors combined with superhydrophobic/superhydrophilic (SH/SHL) surfaces have shown the ability to detect ultra-low concentrations. In this study, femtosecond laser fabricated hybrid SH/SHL surfaces with designed patterns are successfully applied to improve the SERS performances. The shape of SHL patterns can be regulated to determine the droplet evaporation process and deposition characteristics. The experimental results show that the uneven droplet evaporation along the edges of non-circular SHL patterns facilitates the enrichment of analyte molecules, thereby enhancing the SERS performance. The highly identifiable corners of SHL patterns are beneficial for capturing the enrichment area during Raman tests. The optimized 3-pointed star SH/SHL SERS substrate shows a detection limit concentration as low as 10-15 M by using only 5 µL R6G solutions, corresponding to an enhancement factor of 9.73 × 1011. Meanwhile, a relative standard deviation of 8.20% can be achieved at a concentration of 10-7 M. The research results suggest that the SH/SHL surfaces with designed patterns could be a practical approach in ultratrace molecular detections.

Single-pass cutting of frosted glass via change of laser incident medium.

We report a water medium-assisted composite laser cutting (WMACLC) technology for what is believed to be the first time to achieve single-pass separation of frosted glass (FG). The water medium was used to flatten the surface of FG to reduce the diffuse reflection and random refraction of the incident laser. The simulation results of picosecond pulsed laser Bessel beam (PPLBB) intensity distribution in FG showed that the peak intensity in the presence of water can reach about 24 times and 2.3 times that in the absence of water when the PPLBB is 0.08 mm and 0.3 mm below the upper surface of FG, respectively. A PPLBB with higher intensity can be formed along the thickness direction to realize the material modification. A coaxial CW laser provides the thermal tensile stress required for separation. Finally, high-quality separation of FG was achieved using the WMACLC technology with a speed of 50 mm/s. No deviation in the separation track and no edge collapse occurred. The roughness Sa of the separated sidewall is less than 0.3 µm.

Tunable metasurface for independent controlling radar stealth properties via geometric and propagation phase modulation.

Metasurfaces have been verified as an ideal way to control electromagnetic waves within an optically thin interface. In this paper, a design method of a tunable metasurface integrated with vanadium dioxide (VO2) is proposed to realize independent control of geometric and propagation phase modulation. The reversible conversion of VO2 between insulator phase and metal phase can be realized by controlling the ambient temperature, which enables the metasurface to be switched quickly between split-ring and double-ring structures. The phase characteristics of 2-bit coding units and the electromagnetic scattering characteristics of arrays composed of different arrangements are analyzed in detail, which confirms the independence of geometric and propagation phase modulation in the tunable metasurface. The experimental results demonstrate that the fabricated regular array and random array samples have different broadband low reflection frequency bands before and after the phase transition of VO2, and the 10 dB reflectivity reduction bands can be switched quickly between C/X and Ku bands, which are in good agreement with the numerical simulation. This method realizes the switching function of metasurface modulation mode by controlling the ambient temperature, which provides a flexible and feasible idea for the design and fabrication of stealth metasurfaces.

High-performance anti-reflection micro-forests on aluminium alloy fabricated by laser induced competitive vapor deposition.

Surfaces with strong anti-reflection properties have attracted the wide attention of scientists and engineers due to their great application potential in many fields. Traditional laser blackening techniques are limited by the material and surface profile, which are not able to be applied to film and large-scale surfaces. Inspired by the rainforest, a new design for anti-reflection surface structures was proposed by constructing micro-forests. To evaluate this design, we fabricated micro-forests on an Al alloy slab by laser induced competitive vapor deposition. By controlling the deposition of the laser energy, the surface can be fully covered by forest-like micro-nano structures. The porous and hierarchical micro-forests performed a minimum and average reflectance of 1.47% and 2.41%, respectively, in the range of 400-1200 nm. Different from the traditional laser blackening technique, the micro-scaled structures were formed due to the aggregation of the deposited nanoparticles instead of the laser ablation groove. Therefore, this method would lead to little surface damage and can also be applied to the aluminum film with a thickness of 50 µm. The black aluminum film can be used to produce the large-scale anti-reflection shell. Predictably, this design and the LICVD method are simple and efficient, which can broaden the application of the anti-reflection surface in many fields such as visible-light stealth, precision optical sensors, optoelectronic devices, and aerospace radiation heat transfer device.

Large scanning field laser concurrent drilling system with a five-axis independent control for special-shaped holes.

Five-axis laser scanning technology is an effective drilling method for special-shaped holes. Due to a gap in laser angle-of-incidence (AOI) control within a large scanning field, current technologies are challenging for fabricating large-size holes or special-shaped hole arrays. In this paper, a large scanning field five-axis laser concurrent drilling system was proposed. The laser AOI was independently controlled using two pairs of synchronous deflection mirrors. The laser control deviations under a large scanning field were investigated systematically by simulation and experiment. By establishing a complete correction method, the laser AOI control within a scanning field diameter of up to 35 mm was achieved. A series of special-shaped holes were fabricated concurrently on a 3.6 mm thick glass fiber reinforced plastic (GFRP), verifying that the AOI can be controlled by the five-axis laser scanning system. Our work provides a novel method to increase the scanning field of the five-axis laser scanning technology, expanding the application scope of the five-axis laser processing.

High-Responsivity Multiband and Polarization-Sensitive Photodetector Based on the TiS3/MoS2 Heterojunction.

Two-dimensional (2D) material photodetectors have received considerable attention in optoelectronics as a result of their extraordinary properties, such as passivated surfaces, strong light-matter interactions, and broad spectral responses. However, single 2D material photodetectors still suffer from low responsivity, large dark current, and long response time as a result of their atomic-level thickness, large binding energy, and susceptibility to defects. Here, a transition metal trichalcogenide TiS3 with excellent photoelectric characteristics, including a direct bandgap (1.1 eV), high mobility, high air stability, and anisotropy, is selected to construct a type-II heterojunction with few-layer MoS2, aiming to improve the performance of 2D photodetectors. An ultrahigh photoresponsivity of the TiS3/MoS2 heterojunction of 48 666 A/W at 365 nm, 20 000 A/W at 625 nm, and 251 A/W at 850 nm is achieved under light-emitting diode illumination. The response time and dark current are 2 and 3 orders of magnitude lower than those of the current TiS3 photodetector with the highest photoresponsivity (2500 A/W), respectively. Furthermore, polarized four-wave mixing spectroscopy and polarized photocurrent measurements verify its polarization-sensitive characteristics. This work confirms the excellent potential of TiS3/MoS2 heterojunctions for air-stable, high-performance, polarization-sensitive, and multiband photodetectors, and the excellent type-II TiS3/MoS2 heterojunction system may accelerate the design and fabrication of other 2D functional devices.

Rapid fabrication of large-area concave microlens arrays on silica glasses by femtosecond laser bursts.

An efficient and flexible method using femtosecond laser bursts assisted by wet etching is presented to fabricate large-area high-quality microlens arrays (MLAs) on a silica glass surface. In this method, femtosecond laser bursts can ablate micro craters on silica glass in a fast, single-step process by controlling the electron density and a high-speed scanning galvanometer, and the influence mechanism of the number of pulses within a burst on the accuracy and quality of micro craters is analyzed in detail. The experimental results show that the preparation efficiency of micro craters is significantly improved to approximately 32,700 per second. By subsequent acid etching, concave microlenses with controllable dimensions, shapes, and alignments are easily obtained. A large area close-packed hexagonal concave MLA is successfully fabricated by using this method and shows high surface quality and uniformity, which excellently demonstrates the feasibility and flexibility of rapidly fabricating MLAs in the burst regime.

3D printing of nanowrinkled architectures via laser direct assembly.

Structural wrinkles in nature have been widely imitated to enhance the surface functionalities of objects, especially three-dimensional (3D) architectured wrinkles, holding promise for emerging applications in mechanical, electrical, and biological processes. However, the fabrication of user-defined 3D nanowrinkled architectures is a long-pending challenge. Here, we propose a bottom-up laser direct assembly strategy to fabricate multidimensional nanowrinkled architectures in a single-material one-step process. Through the introduction of laser-induced thermal transition into a 3D nanoprinting process for leading the point-by-point nanoscale wrinkling and the self-organization of wrinkle structures, we have demonstrated the program-controlled and on-demand fabrication of multidimensional nanowrinkled structures. Moreover, the precise control of wrinkle morphology with an optimal wavelength of 40 nanometers and the regulation of the dynamic transformation of wrinkled cellular microstructures via interfacial stress mismatch engineering have been achieved. This study provides a universal protocol for constructing nearly arbitrary nanowrinkled architectures and facilitates a new paradigm in nanostructure manufacturing.

Composite laser beam separation technology for brittle transparent materials.

By combining a picosecond Bessel laser and a continuous-wave (CW) fiber Gaussian laser with the same optical axis, a composite laser beam separation (CLBS) technology that allows the fast, high-quality separation of brittle transparent materials was developed for the first time, to the best of our knowledge. In this experiment, 1-mm-thick soda lime glass was separated using this CLBS technology, and the CLBS separation mechanism was analyzed. The experimental results show that a separated surface similar to frosted polishing can be obtained by CLBS, and the edge chipping of the separated upper surface was no more than 0.5 µm. The separated sidewall was flat and smooth without separation defects such as cracks or broken edges, and the surface roughness (Ra) was 0.12 µm. The separation speed reached 12 mm/s and can be further improved by increasing the CW laser power density. This research provides a new way for lasers to separate brittle transparent materials.

Rapid In-Situ Synthesis and Patterning of Edge-Unsaturated MoS2 by Femtosecond Laser-Induced Photo-Chemical Reaction.

Molybdenum disulfide (MoS2) is a representative transition metal sulfide that is widely used in gas and biological detection, energy storage, and integrated electronic devices due to its unique optoelectrical and chemical characteristics. To advance toward the miniaturization and on-chip integration of functional devices, it is strategically important to develop a high-precision and cost-effective method for the synthesis and integration of MoS2 patterns and functional devices. Traditional methods require multiple steps and time-consuming processes such as material synthesis, transfer, and photolithography to fabricate MoS2 patterns at the desired region on the substrate, significantly increasing the difficulty of manufacturing micro/nanodevices. In this work, we propose a single-step femtosecond laser-induced photochemical method which can realize the fabrication of arbitrary two-dimensional edge-unsaturated MoS2 patterns with high efficiency in microscale. Based on this method, MoS2 can be synthesized at a rate of 150 µm/s, 2 orders of magnitude faster than existing laser-based thermal decomposition methods without sacrificing the resolution and quality. The morphology and roughness of the MoS2 pattern can be controlled by adjusting the laser parameters. Furthermore, the femtosecond laser direct writing (FLDW) method was used to fabricate microscale MoS2-based gas detectors that can detect a variety of toxic gases with high sensitivity up to 0.5 ppm at room temperature. This FLDW method is not only applicable to the fabrication of high-precision MoS2 patterns and integrated functional devices, it also provides an effective route for the development of other micro/nanodevices based on a broad range of transition metal sulfides and other functional materials.

An ultrathin memristor based on a two-dimensional WS2/MoS2 heterojunction.

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.