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Evolution mechanism of InGaN quantum dots and their optical properties
摘要： InGaN self-assembled quantum dots (QDs) have been grown by metal-organic chemical vapor deposition. The surface morphologies of InGaN QDs were investigated for different number of periods in the range of one to five. Interfacial formation mechanism of InGaN QDs was investigated by phase separation theory and different strain in active zone. In-rich localized states and interfacial atomic images were observed by spherical aberration corrected transmission electron microscopy. Furthermore, the formation mechanism of InGaN QDs was discussed according to growth kinetics of indium (In) atom migration. The optical properties of QDs-like were tested by temperature-dependent photoluminescence. These results show internal quantum efficiency increases with increasing periodicity owing to increasing total accumulated strain. QDs are formed spontaneously owing to indium composition fluctuations in InGaN layer. The variations of peak energy with increasing temperature are explained by carrier dynamics as a result of size inhomogeneity and carrier localization in InGaN/GaN active zone. These results provide experimental data and theoretical basis for fabricating high quality InGaN QDs.
关键词： Quantum dots,Evolution mechanism,InGaN,Optical properties
更新于2025-09-12 10:27:22
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Influence of laser post-processing on pore evolution of Ti–6Al–4V alloy by laser powder bed fusion
摘要： In laser powder bed fusion (LPBF) processes, critical defect issues such as porosity limit the quality of the fabricated part. This work investigates the mechanism of pore evolution during the laser post-processing of an LPBF part. A laser beam was utilized to scan the top surface of a Ti–6Al–4V alloy part. The morphologies of the internal layers as well as the distribution of the porosity inside the Ti–6Al–4V sample were experimentally measured and compared using micro-computed tomography (micro-CT). It was found that the void fraction was significantly decreased, from 2.51% to 0.77%, by laser post-processing. A multi-physics coupled finite element model based on the Level-set method was built to analyze the evolution mechanism of the pore. This model simulated the effects of the energy density, Marangoni flow and mass transfer on the pore evolution. Typical processes were studied in detail, and a table summarizing the pore evolution under different post-processing parameters is given.
关键词： Ti–6Al–4V alloy,Laser powder bed fusion,Pore evolution,Additive manufacturing,Level-set method
更新于2025-09-12 10:27:22
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A nanoreactor based on SrTiO3 coupled TiO2 nanotubes confined Au nanoparticles for photocatalytic hydrogen evolution
摘要： A TiO2 nanotube-based nanoreactor was designed and fabricated by facile two steps synthesis: firstly, hydrothermal synthesized SrTiO3 was deposited on TiO2 nanotubes (TiO2NTs). Secondly, the Au nanoparticles (NPs) were encapsulated inside the TiO2NTs followed by vacuum-assisted impregnation. The as-synthesized composites were characterized using Transmission electron microscopy (TEM), X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Photoluminescence spectra (PL) and Ultravioletevisible absorption spectroscopy (UVevis). The photocatalytic performance was evaluated by the hydrogen evolution reaction. The results revealed that the SrTiO3 modified TiO2NTs confined Au NPs (STO-TiO2NTs@Au) achieved an enhanced hydrogen evolution rate at 7200 mmol h?1 g?1, which was 2.2 times higher than that of bald TiO2NTs@Au at 3300 mmol h?1 g?1. The improved photocatalytic activity could be attributed to the synergistic effect of the electron-donating of SrTiO3 and TiO2NTs confinement. The as-designed nanoreactor structure provides an example of efficient carriers’ separation photocatalyst.
关键词： Au nanoparticles,Confinement,SrTiO3,TiO2 nanotubes,Photocatalytic hydrogen evolution
更新于2025-09-12 10:27:22
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Parameter extraction of PV models using an enhanced shuffled complex evolution algorithm improved by opposition-based learning
摘要： Accurate and efficient parameter extraction of PV models from I-V characteristic curves is significant for modeling, evaluation and fault diagnosis of PV modules/arrays. Recently, a large number of algorithms are proposed for this problem, but there are still some issues like premature convergence, low accurate and instability. In this paper, a new improved shuffled complex evolution algorithm enhanced by the opposition-based learning strategy (ESCE-OBL) is proposed. The proposed algorithm improves the quality of the candidate solution by the opposition-based learning strategy. Moreover, the basic SCE algorithm evolves with the traditional competition complex evolution (CCE) strategy, but it converges slowly and is prone to be trapped in local optima. In order to improve the exploration capability, the complex in the basic SCE is evolved by a new enhanced CCE. The ESCE-OBL algorithm is compared with some state-of-the-art algorithms on the single diode model (SDM) and double diode model (DDM) using benchmark I-V curves data. The comparison results demonstrate that the proposed ESCE-OBL algorithm can achieve faster convergence, stronger robustness and higher efficiency.
关键词： Parameters extraction,Enhanced shuffled complex evolution (ESCE),Opposition-based learning (OBL)
更新于2025-09-12 10:27:22
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Experimental exploration of mode-locking evolution mechanism in dual-ring fiber laser
摘要： We explored experimentally the mode-locking (ML) evolution mechanism of a dual-ring fiber laser. Increase of the total pump power up to 860 mW allowed the observation of the state changes from single-ring ML, dual-ring ML, to dual-ring self-starting ML. Moreover, a group of wave plates and a fixed polarization beam splitter were applied in each subring as precise attenuators. Rotation of each wave plate for an entire turn allowed the investigation of the ML evolution of the two subrings based on the intracavity power variation in each subring. The variation periodicity of the output power was analyzed for each subring and was found to be consistent with the theoretical results. Furthermore, the ML detachment threshold in each subring was estimated to explain the ML evolution. Our study provides a deeper understanding of the ML evolution in dual-ring fiber lasers and can aid their future optimal design for dual comb applications.
关键词： Fiber lasers,Mode-locking evolution,Cascaded nonlinear processes,Mode-locked lasers,Ultrafast mechanism
更新于2025-09-12 10:27:22
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Analysis of the fracture mechanism at cryogenic temperatures of thick 316LN laser welded joints
摘要： Laser welding of modified 316LN steel with a thickness of 20 mm was conducted using a YLS-20000 fiber laser. The microstructure of the weld joint was characterized and tensile and fracture toughness tests were carried out. The microstructure evolution of the fracture specimens was studied systematically to elucidate the fracture mechanism. The weld was composed of the single austenite phase and was characterized by cellular and columnar grains, and the grain size became coarser with a weak orientation. The Rm values of the laser welded joints were almost equal to that of the base metal both at RT and 4.2 K, and the fracture surfaces were featured by ductile fracture with quantities of dimples and microvoids. The fracture toughness of the weldments decreased to ?84% of that of the parent metal at 4.2 K. Enhancement of the fracture toughness was attributed predominantly to the presence of twins and to the fine grain size, and the reduction was caused by the partially stress-induced phase transformation of the austenite to martensite. The synergistic effects of these factors result in a favorable improvement in the fracture toughness of the weldment.
关键词： Fracture mechanism,Mechanical properties,Thick plates,Laser welding,Cryogenic temperature,Microstructure evolution
更新于2025-09-12 10:27:22
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Residual Stress Modelling and Experimental Analyses of Ti6Al4V ELI Additive Manufactured by Laser Engineered Net Shaping
摘要： This paper focus on the experimental analyses and modelling of the residual stresses build up during laser additive manufacturing by Laser Engineered Net Shaping. Currently, additive manufactured parts employ heat treatment for the reduction of internal stresses, but then additional advantages are also possible from heat treatment. The experimental analyses focus on stress relieving heat treatment temperatures to reduce the residual stresses during laser processing of LENS Ti6Al4V ELI specimens. LENS parts out of Ti6Al4V ELI will illustrate the mechanical property possibilities resulting from the selected stress relieving heat treatments in this study. The primary aim of heat treatment in this case of Ti6Al4V ELI is the reduction of internal stresses. Due to the mechanical behaviour of Ti6Al4V as built additive manufactured parts, the heat treatment seems to be necessary to increase the mechanical behaviour, such as the fatigue performance and the breaking elongation. Optical Microscope, Scanning Electron Microscope and Vickers hardness test was employed to carry out detailed study of the resulting microstructures and Hardness. The model by COMSOL Multiphysics was employed to predict the residual stresses of as built LENS Ti6Al4V ELI and to better understand the residual stresses amounts in the Ti6Al4V ELI alloy that need to be minimized by heat stress relieving heat treatment methods. The results included the β-phase that formed in the stress relieving heat treatment process that was transformed to martensite α during the cooling process and a fine basket-weave structure emerged. The microhardness of LENS Ti6Al4V ELI alloy gradually decreased with increasing stress relieving heat treatment temperature. The computed model revealed the maximum stress of 1.78x109 MPa, the Model strongly recommended the LENS process parameters suitable to obtain Ti6Al4V ELI samples with minimal residual stresses and a further possible method to alleviate the attained residual stresses in the model to the desired elasticity.
关键词： Modelling,Additive manufacturing,Residual stresses,Heat treatment,Microstructure evolution,Laser Engineered Net Shaping (LENS)
更新于2025-09-12 10:27:22
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Type-II heterostructures of <b>α</b> -V <sub/>2</sub> O <sub/>5</sub> nanowires interfaced with cadmium chalcogenide quantum dots: Programmable energetic offsets, ultrafast charge transfer, and photocatalytic hydrogen evolution
摘要： We synthesized a new class of heterostructures by depositing CdS, CdSe, or CdTe quantum dots (QDs) onto α-V2O5 nanowires (NWs) via either successive ionic layer adsorption and reaction (SILAR) or linker-assisted assembly (LAA). SILAR yielded the highest loadings of QDs per NW, whereas LAA enabled better control over the size and properties of QDs. Soft and hard x-ray photoelectron spectroscopy in conjunction with density functional theory calculations revealed that all α-V2O5/QD heterostructures exhibited Type-II band offset energetics, with a staggered gap where the conduction- and valence-band edges of α-V2O5 NWs lie at lower energies (relative to the vacuum level) than their QD counterparts. Transient absorption spectroscopy measurements revealed that the Type-II energetic offsets promoted the ultrafast (10?12–10?11 s) separation of photogenerated electrons and holes across the NW/QD interface to yield long-lived (10?6 s) charge-separated states. Charge-transfer dynamics and charge-recombination time scales varied subtly with the composition of heterostructures and the nature of the NW/QD interface, with both charge separation and recombination occurring more rapidly within SILAR-derived heterostructures. LAA-derived α-V2O5/CdSe heterostructures promoted the photocatalytic reduction of aqueous protons to H2 with a 20-fold or greater enhancement relative to isolated colloidal CdSe QDs or dispersed α-V2O5 NWs. The separation of photoexcited electrons and holes across the NW/QD interface could thus be exploited in redox photocatalysis. In light of their programmable compositions and properties and their Type-II energetics that drive ultrafast charge separation, the α-V2O5/QD heterostructures are a promising new class of photocatalyst architectures ripe for continued exploration.
关键词： α-V2O5 nanowires,cadmium chalcogenide quantum dots,photocatalytic hydrogen evolution,programmable energetic offsets,Type-II heterostructures,ultrafast charge transfer
更新于2025-09-12 10:27:22
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High photoresponse and fast carrier mobility: Two‐dimensional rGO‐AgBr/Ag composite based on Z‐scheme heterointerface with plasma for hydrogen evolution
摘要： With the improvement of people's living standard, energy shortage is increasingly severe. Photocatalysis technology is one of the most effective means to solve this problem. Generally, poor visible‐light response and fast combination of photo‐induced carriers are the main limiting factors to traditional photocatalysts. Aiming at this problem, in this paper, AgBr was used as the photosensitizer to immobilize on the surface of reduced graphene oxide (rGO) for the complexation of Ag+ ions and carboxyl groups of precursor graphene oxide (GO), then the two‐dimensional rGO‐AgBr/Ag composites (2D rGAA‐α, α = 1, 2 and 3) were synthesized by solvothermal method. The structures, morphologies, chemical bonding states and photoelectrochemical properties of the samples were analyzed to study the samples, and the corresponding visible‐light‐driven (VLD) catalytic performances were studied by hydrogen evolution reaction (HER). Compared with pure rGO, the light absorption of rGAA‐α was almost extended to full spectral range for the Z‐scheme heterointerface (rGO‐AgBr) construction, and the separation of photo‐induced carriers can be promoted effectively. The HER results showed that the average hydrogen evolution rate ( Rp) of rGAA‐α was significantly increased, and the rGAA‐2 catalyst presented the highest Rp (72.71 μmol ‐1). After six recycling experiments, the very faint activity decrease and ‐1g h unobvious structure change suggested the high photostability. Accordingly, the enhanced catalytic activity of rGAA‐α catalysts was attributed to the formation of Z‐scheme heterointerface and generation of Ag plasmas, so this study will provide a simple, effective and promising method for hydrogen energy development.
关键词： AgBr,heterostructure,Ag plasma,hydrogen evolution,reduced graphene oxide
更新于2025-09-12 10:27:22
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Enhanced photocatalytic hydrogen evolution over TiO2/g-C3N4 2D heterojunction coupled with plasmon Ag nanoparticles
摘要： 2D heterojunction based on g-C3N4 nanosheets with other semiconductor nanosheets is a promising way to improve photocatalytic hydrogen evolution (PHE) activity over g-C3N4. However, current 2D heterojunction based on g-C3N4 are unsatisfactory due to their insu?cient absorption of visible light and ine?cient charge separation. In this work, Ag/TiO2/g-C3N4 nanocomposites based on 2D heterojunction coupling with Ag surface plasmon resonance (SPR) were synthesized by a method combining facile wetness impregnation calcination. The PHE activity of Ag/TiO2/g-C3N4 nanocomposites is attributed to the TiO2/g-C3N4 2D heterojunction and bare g-C3N4 nanosheet under visible light irradiation, indicating a cooperative e?ect between Ag and TiO2/g-C3N4 2D heterojunction. As a result of SPR e?ect, the composites strongly absorb visible light. In addition, the oscillating hot electrons from Ag can easily transfer to 2D heterojunction. This synergistic e?ect lead to su?cient visible light absorption and e?cient charge separation of 2D heterojunction, which improved the PHE activity of g-C3N4. This work indicates that loading metal nanoparticles on 2D heterojunction as metal SPR-2D heterojunction nanocomposites may be a potential method for harvesting visible light for PHE.
关键词： Surface plasmon resonance,Photocatalytic hydrogen evolution,TiO2,2D heterojunction,g-C3N4
更新于2025-09-12 10:27:22