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Addressing the Reliability and Electron Transport Kinetics in Halide Perovskite Film via Pulsed Laser Engineering
摘要： The long-term performance and stability of perovskites are adversely affected by their porous microstructure, tensile residual stress, and electron transport kinetics. Here, a high-speed pulsed laser processing technique is implemented to produce beneficial structural changes in organic–inorganic halide perovskites, including pore-free, crystalline structure, reduced defects, and tensile residual stress. Moreover, halide perovskite films can be converted from p-type to n-type semiconductor, which originates from crystal structure changes, giving rise to carrier dynamic changes. Comparing with traditional thermal annealing, residual tensile stress of perovskite thin film decreases by 40% after pulse laser processing, which significantly increases its stability. Pulse-laser-induced thermomechanical shock momentum can create pore-free perovskite thin films, contributing to much better reliability. Under humidity of 80% at room temperature for 500 h, the decomposition rate is reduced by more than two times, comparing thin films after pulsed laser processing with conventional thermal annealing. The thermal decomposition temperature of pulse-laser-processed perovskite thin film raises by 20 to about 220 °C. Pulse laser processing technique provides a scalable technique to tailor the structures in perovskite films with both temperature and loading control, further facilitates the design of perovskite-based devices for service under harsh conditions, and also contributes to high-performance optoelectronic applications.
关键词： semiconductors,perovskites,stability,microstructures,residual stress
更新于2025-11-14 15:24:45
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Crack Restraining Methods and their Effects on the Microstructures and Properties of Laser Cladded WC/Fe Coatings
摘要： Laser cladded WC/Fe coatings have the advantages of low cost and high abrasion wear resistance. However, cracks always appear in WC/Fe coatings, which limits their industrial application. In this paper, the co-effects of the re-melting process, heat treatments, and amount of Co element on the cracking susceptibility, microstructures, and mechanical properties of WC/Fe laser cladding coatings were studied. Experimental results show that re-melting process is helpful to improve the surface quality of the coating and to reduce the cracking susceptibility. The hardness of the coating decreases slightly but distributes more uniformly. Cracks in the coating can be inhibited effectively by preheating the substrate to 250 ?C and maintaining the temperature during the laser cladding process, as well as applying an annealing treatment at 300 ?C for 1 h. Heat treatment also results in a slight decrease in the hardness. Crack initiation cannot be restrained completely by applying the above two methods when laser cladding a big area of coating. On the basis of the above two methods, addition of Co element to the coating can further improve its toughness and decrease the crack susceptibility. Crack-free WC/Fe coating can be manufactured when 8% Co is added, and its wear resistance is much better than that of the hardened medium steel, especially when the wear time is long.
关键词： Laser Cladding,mechanical properties,microstructures,WC/Fe coating,crack restraining methods
更新于2025-09-23 15:23:52
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Artifacts in Transient Absorption Measurements of Perovskite Films Induced by Transient Reflection from Morphological Microstructures
摘要： Organolead halide perovskites MAPbX3 (MA = CH3NH3+; X = Cl?, Br?, I?) have attracted broad tremendous interest in the past 10 years for applications in solar cells and light-emitting devices. In evaluating the quality of the perovskite materials, spectroscopic characterizations such as static and time-resolved absorption and photoluminescence measurements are essential to examine their photophysical properties. A recent report found that the correct measurement of static absorption spectra of MAPbX3 films is indeed difficult due to the strong light scattering caused by their poor surface coverage or complex microstructures. These morphological complexities seem to be inevitable in thin-film fabrication and should not only affect the steady-state spectroscopic measurements but also can significantly impact the time-resolved spectroscopic characterizations, whose results are crucial for understanding photoinduced carrier dynamics in the examined materials. Photoexcited states in semiconductor materials induce changes in the real and imaginary parts of the dielectric function. This leads to changes in absorption (imaginary part) and reflectivity (real part), which can be substantial for materials with significant values of refractive index such as lead halide perovskites. Transient absorption (TA) spectroscopy is a typical technique that has been broadly used to probe photoexcited state dynamics in perovskites and other semiconductor materials. In TA measurements, a pump laser pulse is used to excite the perovskite films, and the induced absorption changes (ΔA) are recorded as a function of both wavelength and time. With the transmitted light as the probe (Figure 1a), the TA signal (ΔA) is mainly decided by the ratio of the intensity of transmitted probe light with and without pump excitation (see eq S1 in the SI), assuming that the loss of transmitted probe light completely results from the sample absorption. On the basis of the same experimental setup, transient reflection (TR) measurements can also be carried out by using the reflected probe light as detection signal (Figure 1b). The TR signal (ΔR/R) can also be determined by the ratio of the intensity of reflected probe light with and without pump excitation (see eq S4 in the SI). Unlike the TA measurements that mainly probe the bulk property of samples, the TR signal mainly detects the photoinduced reflection variations due to the refractive index change at the sample surface. Therefore, the TR spectrum and kinetics can be significantly different from those of TA even in the same sample. For example, previous TA and TR measurements have found dramatically faster carrier recombination kinetics on the surface than in the bulk of MAPbX3 perovskite films or single crystals because of the presence of more surface defects. There is an abnormal case in the regular TA measurements particularly when performed on the films with large and heterogeneous microstructures (e.g., films with poor coverage, large grains, and pinholes) because the loss of transmitted probe light in their TA measurements likely results not only from the sample absorption but also from the reflection of the film surface or the boundary of microstructures in samples. In this case, the measured transient spectrum, though collected in the transmittance mode as in TA, can contain contributions from both TA and TR signals (see Figure 1c and eq S6 in the SI). This could lead to distorted TA spectra and thus inaccurate analysis of photoinduced kinetics. A solution-processed organic or inorganic halide perovskite thin film is a typical material whose morphological microstructures were found to have significant impact on device performance. Although the photoinduced carrier dynamics in perovskite films has been extensively studied using TA spectroscopy, the possible artifacts in TA results induced by TR signal originating from the photoinduced reflectivity variation of film surfaces and microstructures have been overlooked. Herein, in order to clarify the influence of TR signal in the regular TA measurements, we performed a careful transient spectroscopic analysis on a series of MAPbBr3 perovskite films with different microstructure morphology. Meanwhile, TR measurements on MAPbBr3 single crystals (SCs) were carried out for comparison. We confirmed that the TA spectra measured in MAPbBr3 perovskite films with large and heterogeneous microstructures do comprise non-negligible TR signals from the photoinduced reflection of microstructures, with the weight of contribution increased from ～20 to ～100% as the size of the microstructure increased from <200 nm to 1?2 μm. The presence of TR signal leads to an “artifact” feature in the TA spectra and faster observed kinetics owing to the faster surface carrier recombination, which will thus mislead the analysis of bulk carrier dynamics. We also provided a method to reduce the TR signal in actual TA measurements by adding solvent with its refractive index close to the samples, by which the TR distortion can be suppressed to some extent.
关键词： artifacts,transient reflection,transient absorption,carrier dynamics,perovskite films,microstructures
更新于2025-09-23 15:23:52
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Designing bacterial chemotactic receptors guided by photonic femtoliter well arrays for quantifiable, label-free measurement of bacterial chemotaxis
摘要： Whole cell bioreporters, such as bacterial cells, can be used for environmental and clinical sensing of specific analytes. However, the current methods implemented to observe such bioreporters in the form of chemotactic responses heavily rely on microscope analysis, fluorescent labels, and hard-to-scale microfluidic devices. Herein, we demonstrate that chemotaxis can be detected within minutes using intrinsic optical measurements of silicon femtoliter well arrays (FMAs). This is done via phase-shift reflectometric interference spectroscopic measurements (PRISM) of the wells, which act as silicon diffraction gratings, enabling label-free, real-time quantification of the number of trapped bacteria cells in the optical readout. By generating unsteady chemical gradients over the wells, we first demonstrate that chemotaxis towards attractants and away from repellents can be easily differentiated based on the signal response of PRISM. The lowest concentration of chemorepellent to elicit an observed bacterial response was 50 mM, while the lowest concentration of chemoattractant to elicit a response was 10 mM. Second, we employed PRISM, in combination with a computational approach, to rapidly scan for and identify a novel synthetic histamine chemoreceptor strain. Consequently, we show that by using a combined computational design approach, together with a quantitative, real-time, and label-free detection method, it is possible to manufacture and characterize novel synthetic chemoreceptors in Escherichia coli (E. coli).
关键词： diffraction,synthetic biology,optical biosensor,chemotaxis,microstructures
更新于2025-09-23 15:23:52
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Novel design of photocatalyst coaxial ferromagnetic core and semiconducting shell microwire architecture
摘要： We report a novel design of coaxial core-shell magnetic-semiconductor microwire, as a catalyst under sunlight irradiation. The nano/micro hierarchical architecture-like device is comprised of a coaxial core-shell microwire where the core is the ferromagnetic Fe metal and the shell is formed by a semiconducting hematite layer. The fabrication process of our substrate-free device is simply based on controlled thermal oxidation process revealing a simple and low-cost method. The hematite outer microlayer has a mesoporous structure decorated with nanowires. The ferromagnetic and metallic core assume fundamental importance as to mechanical stability, collect the generated photoelectrons, and to be removed back from the dye solution by a magnetic field gradient or simply a magnet. This nano/micro device has exhibited photocatalytic activity to degrade the methylene blue dye under simulated sunlight irradiation. Additionally, the coaxial magnetic/semiconducting can also be designed as a photoanode to drive water oxidation reaction. The coaxial magnetic/semiconducting photoanode response has shown good chemical stability and long activity under simulated sunlight radiation. In fact, this designed architecture gives novel perspective in the development of substrate free photocatalyst.
关键词： Photoelectrochemical performance,Hematite photoanodes,Photodegradation,Micro/nano architecture,Core-shell microstructures,Thermal oxidation
更新于2025-09-23 15:23:52
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Fabrication of thin-film spherical anodic alumina oxide templates using a superimposed nano-micro structure
摘要： Compared to the single-scale planar anodic aluminum oxide (AAO) film, the multi-scale hierarchical AAO structures can have a better performance due to the larger surface area. The conventional multi-scale AAO structure on a micro-pattern surface was fabricated using time-consuming lithography and etching process at high cost. In this article, the 3D porous AAO films with nanopores of 35~45 nm in diameter have been achieved on the surface of silica micro beads of 2 μm in diameter. The superimposed nano-micro structure was fabricated using hybrid-pulse anodizing the sputtered Al film on beads with a period of negative potential to dissipate Joule heating at room temperature. The 3D AAO-on-beads structure provides a large-surface-area substrate for enhancing the sputtered TiO2 photocatalysis. The photocatalysis on the superimposed nano-micro structures can exhibit a high performance with the MB concentration of 30% after 15 hr photo-degradation.
关键词： AAO,nano-microstructures,anodic aluminum oxide,nanoporus alumina,micro bead
更新于2025-09-23 15:23:52
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Controlling the shape of 3D microstructures by temperature and light
摘要： Stimuli-responsive microstructures are critical to create adaptable systems in soft robotics and biosciences. For such applications, the materials must be compatible with aqueous environments and enable the manufacturing of three-dimensional structures. Poly(N-isopropylacrylamide) (pNIPAM) is a well-established polymer, exhibiting a substantial response to changes in temperature close to its lower critical solution temperature. To create complex actuation patterns, materials that react differently with respect to a stimulus are required. Here, we introduce functional three-dimensional hetero-microstructures based on pNIPAM. By variation of the local exposure dose in three-dimensional laser lithography, we demonstrate that the material parameters can be altered on demand in a single resist formulation. We explore this concept for sophisticated three-dimensional architectures with large-amplitude and complex responses. The experimental results are consistent with numerical calculations, able to predict the actuation response. Furthermore, a spatially controlled response is achieved by inducing a local temperature increase by two-photon absorption of focused light.
关键词： light-induced actuation,pNIPAM,temperature response,stimuli-responsive materials,gray-tone lithography,hetero-microstructures,laser lithography,3D microstructures
更新于2025-09-23 15:22:29
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Manufacturing profile-free copper foil using laser shock flattening
摘要： Copper foil is a key material of printed circuit boards and plays an important role in the conductance of electric circuits and interconnection of electronic components. When high-frequency signals were transmitted in rough copper foil wires, the conductor resistance, wire loss, and signal loss increased because of the skin effect. To reduce the negative influence of the skin effect and improve the quality of the copper foil, a laser shock flattening (LSF) method was proposed to manufacture profile-free copper foil with high performance. It was concluded that the better flattening effect for large-area profile-free copper foil could be achieved at a pulse energy of 0.25 J and an overlap rate of 25%, and its surface roughness decreased by 67.0% from 52.1 nm to 17.2 nm. Subsequently, to determine the mechanism for the flattened deformation of copper foil induced by LSF, the microstructures of the copper foil before and after flattening were characterised using transmission electron microscopy. A higher dislocation density and a few deformation twins were found in the profile-free copper foil. Ultimately, nano-indentation, micro-tensile, and electrochemical corrosion tests indicated that the mechanical properties and corrosion resistance of the copper foil were significantly improved by LSF. This technique would enable the successful fabrication of large-area profile-free copper foil with high performance for the emerging applications of ultra-high-frequency signal communication and printed circuit board manufacture.
关键词： Corrosion resistance,Mechanical properties,Flattened deformation mechanism,Microstructures,Laser shock flattening,Profile-free copper foil
更新于2025-09-23 15:21:01
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Fabrication of Polymer Microstructures of Various Angles via Synchrotron X-Ray Lithography Using Simple Dimensional Transformation
摘要： In this paper, we developed a method of fabricating polymer microstructures at various angles on a single substrate via synchrotron X-ray lithography coupled with simple dimensional transformations. Earlier efforts to create various three-dimensional (3D) features on flat substrates focused on the exposure technology, material properties, and light sources. A few research groups have sought to create microstructures on curved substrates. We created tilted microstructures of various angles by simply deforming the substrate from 3D to two-dimensional (2D). The microstructural inclination angles changed depending on the angles of the support at particular positions. We used convex, concave, and S-shaped supports to fabricate microstructures with high aspect ratios (1:11) and high inclination angles (to 79?). The method is simple and can be extended to various 3D microstructural applications; for example, the fabrication of microarrays for optical components, and tilted micro/nanochannels for biological applications.
关键词： curved substrate,microstructures,lithography,Synchrotron X-rays
更新于2025-09-23 15:21:01
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Intimate contact development during laser assisted fiber placement: Microstructure and effect of process parameters
摘要： Intimate contact development under LAFP-specific thermal and mechanical boundary conditions/interactions and the effect of process parameters are investigated. One-layer, unidirectional strips of CF/PEKK material were placed with different process parameters on a flat tool surface to create different intimate contact conditions. The concept of effective intimate contact, which is based on the resin content at the surface, is introduced and a methodology to measure it from surface micrographs is provided. Degree of effective intimate contact measured from the samples was compared with the existing intimate contact models. The temperature history in the compaction zone was estimated with a finite element model and pressure sensitive films were used to determine the compaction pressure. It is shown that in addition to the squeeze flow mechanism, which is the base for the current intimate contact models, through-thickness percolation flow of the resin needs to be considered to explain the effective intimate contact development.
关键词： B. Microstructures,C. Process modeling,E. Automated fiber placement (AFP),A. Polymer-matrix composites (PMCs)
更新于2025-09-23 15:21:01