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Effects of titanium on grain boundary strength in molybdenum laser weld bead and formation and strengthening mechanisms of brazing layer
摘要： Molybdenum has tremendous application potential in the nuclear power field, but its application is limited by the grain-boundary embrittlement of fusion-welded joints made of it. In this study, titanium was selected as an alloying element to reduce brittleness of laser weld beads in molybdenum "cladding-end plug" socket joints. Brazing was also performed to enhance the joint strength. Joints with the same strength as base material and a hydraulic bursting pressure of 60 MPa were produced using a combination of the two methods. The analysis indicates the following. After being added to the weld bead, titanium was able to combine with the free oxygen, forming TiO2 and reducing the MoO2 content on grain boundary surface. Oxygen and MoO2 are both the main causes of the embrittlement of molybdenum grain boundaries. In addition, by taking advantage of the high melting point and thermal conductivity of molybdenum, a titanium foil pre-placed between the tube and rod in the socket joint was melted, forming metallurgical bonding, which further improved the bearing capacity of the joint.
关键词： laser beam welding,titanium,brazing,molybdenum,grain boundary embrittlement
更新于2025-11-28 14:24:20
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Enhanced mechanical performance of fusion zone in laser beam welding joint of molybdenum alloy due to solid carburizing
摘要： It is unable to strengthen molybdenum (Mo) through solid-state phase transformation, while exploring the effect of carbon (C) on microstructures and properties of fusion zone (FZ) of laser beam welding (LBW) joints of Mo alloy with serious grain boundary embrittlement is significant. An analysis was made on changes of bonding strength of grain boundary and precipitates on the grain boundary surface in the FZ of Mo carburized welded joints, and the existing form and strengthening mechanism of carbon. At first, solid carburizing (SC) can achieve the goal of adding the C to welded joints and C mainly appeared as C atoms and Mo2C in Mo alloy. Afterwards, C could increase the grain boundary strength and the plasticity of grains in the FZ. Therefore, the compatibility of deformation at grain boundary and grain interior was improved. Finally, Mo2C distributing at the grain boundary can inhibit the crack propagation during the deformation. As a results, the tensile strength of carburized weld joints rose by 426% compared with that of uncarburized weld joints, meanwhile the above results provide a new idea for the method for strengthening the Mo fusion weld joints.
关键词： laser beam welding,grain boundary embrittlement,carbon,molybdenum
更新于2025-11-28 14:24:20
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Conjugated Polymer–Assisted Grain Boundary Passivation for Efficient Inverted Planar Perovskite Solar Cells
摘要： Grain boundaries in lead halide perovskite films lead to increased recombination losses and decreased device stability under illumination due to defect-mediated ion migration. The effect of a conjugated polymer additive, poly(bithiophene imide) (PBTI), is investigated in the antisolvent treatment step in the perovskite film deposition by comprehensive characterization of perovskite film properties and the performance of inverted planar perovskite solar cells (PSCs). PBTI is found to be incorporated within grain boundaries, which results in an improvement in perovskite film crystallinity and reduced defects. The successful defect passivation by PBTI yields reduces recombination losses and consequently increases power conversion efficiency (PCE). In addition, it gives rise to improved photoluminescence stability and improved PSC stability under illumination which can be attributed to reduced ion migration. The optimal devices exhibit a PCE of 20.67% compared to 18.89% of control devices without PBTI, while they retain over 70% of the initial efficiency after 600 h under 1 sun illumination compared to 56% for the control devices.
关键词： halide perovskites,conjugated polymers,grain boundary passivation,nickel oxide
更新于2025-11-20 15:33:11
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High-Performance Photoresistors Based on Perovskite Thin Film with a High PbI2 Doping Level
摘要： We prepared high-performance photoresistors based on CH3NH3PbI3 ?lms with a high PbI2 doping level. The role of PbI2 in CH3NH3PbI3 perovskite thin ?lm was systematically investigated using scanning electron microscopy, X-ray diffraction, time-resolved photoluminescence spectroscopy, and photoconductive atomic force microscope. Laterally-structured photodetectors have been fabricated based on CH3NH3PbI3 perovskite thin ?lms deposited using precursor solution with various CH3NH3I:PbI2 ratios. Remarkably, the introduction of a suitable amount of PbI2 can signi?cantly improve the performance and stability of perovskite-based photoresistors, optoelectronic devices with ultrahigh photo-sensitivity, high current on/off ratio, fast photo response speed, and retarded decay. Speci?cally, a highest responsivity of 7.8 A/W and a speci?c detectivity of 2.1 × 1013 Jones with a rise time of 0.86 ms and a decay time of 1.5 ms have been achieved. In addition, the local dependence of photocurrent generation in perovskite thin ?lms was revealed by photoconductive atomic force microscopy, which provides direct evidence that the presence of PbI2 can effectively passivate the grain boundaries of CH3NH3PbI3 and assist the photocurrent transport more effectively.
关键词： grain boundary passivation,PC-AFM,photoresistor,high PbI2 doping content
更新于2025-11-14 15:28:36
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Dendritic PAMAM polymers for strong perovskite intergranular interaction enhancing power conversion efficiency and stability of perovskite solar cells
摘要： The modification of perovskite intergranular perovskite/perovskite interface plays a critical role for power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this work, polyamidoamine (PAMAM) dendrimers are utilized as the dendritic crystallization framework templating the perovskite-crystallizing process. The interactions at the perovskite intergranular interface are considerably strengthened at an ambient environment with dendritic PAMAMs crosslinking the perovskite grains. Consequently, the perovskite morphology is remarkably improved by suppressing the grain/grain-aggregate boundaries for the pinhole removal, which produces a compact, uniform and non-pinhole perovskite film. Finally, the strengthened interfacial interactions dramatically enhance the PCE value of unencapsulated PSCs about 42.6% at an ambient condition. Besides, the unencapsulated PAMAM-modified device can keep 73% of initial PCE value in 400 h while the control device decays to 5% of initial PCE value in 50 h. These results reveal that dendritic polymers might remarkably improve the PCE value and the stability of PSCs. This work provides a new molecular design guideline to effectively regulate the perovskite intergranular interfacial interactions.
关键词： Grain boundary,Interfacial interaction,Intergranular interface,Dendrimer,Perovskite solar cell
更新于2025-11-14 15:27:09
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Tailoring metal film texture by use of high atomic mobility at metal-semiconductor interfaces
摘要： The difference in the microstructural and texture evolution of Al films grown on amorphous SiO2 (a-SiO2) and amorphous Ge (a-Ge) substrates have been investigated. Surprisingly, the a-Ge substrate was found to change the preferred orientation of Al grains from the conventional (1 1 1) to the unconventional (1 1 0). The effect of the high mobility of Ge atoms at the metal-semiconductor interface on the microstructural and texture evolution of the metal thin film was studied. The diffusion of the Al adatoms on the a-Ge substrate was suppressed owing to the segregation of Ge atoms at the film surface. The mobility of Al grain boundaries was also suppressed because of grain-boundary wetting by the Ge atoms. It is concluded that the a-Ge substrate could tailor the Al grain orientation from (1 1 1) to (1 1 0) owing to the change in the film-growth mode from three-dimensional to two-dimensional nucleation. The concept of interaction-induced island-growth model, which is based on the Volmer–Weber growth model, is also discussed here. This work thus demonstrates how the atomic mobility at the interface of the metal thin film and the semiconductor substrate controls the film microstructure and texture during deposition.
关键词： Substrate,Microstructure,Surface diffusion,Texture,Metal thin film,Grain-boundary wetting
更新于2025-09-23 15:23:52
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Lattice thermal conduction in suspended molybdenum disulfide monolayers with defects
摘要： In this study, we investigated the effect of lattice defects comprising vacancies and boundaries on the lattice thermal conductivity (LTC), k p, of suspended molybdenum disulfide monolayers (MLs) over a wide temperature range (1 < T < 500 K). By using the phonon Boltzmann formalism, the acoustic phonons were considered to be scattered by the sample and grain boundaries, isotopic impurities, vacancies, and other phonons via Umklapp and normal (N-) processes. k p was evaluated using a modified Callaway model by considering the in-plane longitudinal acoustic and transverse acoustic phonons, and out-of-plane flexural acoustic phonon modes. We demonstrated the need to include the often neglected non-resistive N-processes when evaluating the LTC. Numerical calculations of the temperature dependence of the LTC for crystalline and polycrystalline MoS2 MLs showed the dominance of sample-dependent scattering mechanisms at low temperatures (T < 100 K) and of phonon-phonon scattering at higher temperatures, where the N-processes played an important role. The effects of vacancies and boundaries were to alter the behavior and suppress the magnitude of the LTC. The suppression due to vacancies was greater in crystalline MLs with specular surfaces and in polycrystalline MLs with larger grain sizes. The calculations compared well with recent thermal conductivity data obtained for polycrystalline samples. The need for further investigations is suggested.
关键词： MoS2 monolayer,grain boundary scattering,vacancy scattering,lattice thermal conductivity,N-process
更新于2025-09-23 15:23:52
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Role of carbon-rings in polycrystalline GeSb2Te4 phase-change material
摘要： Carbon (C) is used to increase the overall performance of Ge-Sb-Te (GST) phase-change memory material. Yet the C configuration in polycrystalline GST and its microscopic role is unclear. Using the well-studied GeSb2Te4 as an example, this work unravels the microscopic C doping role based on ab initio calculations. Our results reveal that carbon prefers occupying the interstitials at very low C concentrations, while with a roughly critical C concentration of over 2%, carbon atoms will cluster at the grain boundaries, with very few carbon atoms might exist at the interstitials. With further increasing the C concentrations, C atoms tend to form ring-like configurations in the grain boundaries rather than chain-like configurations. This is due to that the covalent bonds in ring-like configurations are stronger than that in chain-like configurations. Further analysis on the lone-pair electrons and electronic densities of states show that C dopants significantly change the number of lone-pair electrons of surrounding atoms, thus affecting the electronic structure. Finally, the diffusion coefficient of C is estimated to be of the order of 10^-13 m^2/s at 400 K, indicating the good stability of C dopants in GeSb2Te4. Our work provides fundamental understanding on the microscopic role of C doping in GST phase-change materials and benefits for improving the properties of the recording materials by controlling the doping concentration.
关键词： Ab initio molecular dynamic simulations,Ab initio calculations,Phase-change materials,Grain boundary,GeSb2Te4,Carbon doping
更新于2025-09-23 15:23:52
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Tailoring Grain Boundary Chemistry of Polymeric Carbon Nitride for Enhanced Solar H2 Production and CO2 Reduction
摘要： Photocatalytic water splitting is a promising and clean way to mimic the plant photosynthesis in a sustainable manner. Improvements of the quantum efficiency and optical absorption in the relevant range are certainly the further steps to approach practicality. Here, we reported that these issues can be readily addressed when 5-aminotetrazole, a monomer with still higher nitrogen content, is used for the synthesis of carbon nitride. The molten salt mixture NaCl/KCl is used as a high temperature solvent to tailor the grain boundary structure and chemistry. Visible light quantum efficiency for H2 production of 0.65 could be obtained in the presence of K2HPO4 as double layer modifier. This value is very high, considering that this number is a convolute of light to charge couple conversion, charge localization, as well as a successful oxidation and reduction reaction.
关键词： H2 production,Grain boundary,Polymeric carbon nitride,Photocatalysis,Salt melt
更新于2025-09-23 15:22:29
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Comparison of the Optical and Electrical Properties of Al-Doped ZnO Films Using a Lorentz Model
摘要： In this research, zinc oxide (ZnO) films are doped with various amounts of Al dopants, from 0 to 13 at.%, using ion-beam co-sputtering for Zn and Al metallic targets at room temperature. The Al-doped ZnO (AZO) films appear to have lower transmittances in the UV and near-IR ranges. The electrical and optical properties of each film are successfully analyzed by using the spectroscopic ellipsometry of two Lorentz oscillators for the two lower transmittances. The optimal AZO film is deposited with an Al-dopant of 1.5 at.% at an oxygen partial pressure of 0.12 mTorr; it has the smallest resistivity of 7.8 × 10?4 Ω cm and high transmittance of > 80% in the visible regions. The free carrier concentration and mobility evaluated using ellipsometry are different from those measured using the Hall effect. This phenomenon was the result of the grain boundary scattering due to the small ~20-nm grain size of the AZO film used in this study.
关键词： ellipsometry,grain boundary scattering,Hall effect,Lorentz oscillators,Al-doped ZnO,ZnO
更新于2025-09-23 15:22:29