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Directed energy deposition of Al 5xxx alloy using Laser Engineered Net Shaping (LENS??)
摘要： Here, we present directed energy deposition (DED) of wrought-like Al 5xxx AlMg alloy by Laser Engineered Net Shaping (LENS?). A transition from an Al 5083 gas atomized powder feedstock to Al 5754 characteristics of the as-deposited material due to selective evaporation of Mg was observed. Density values obtained by X-ray micro-computed tomography (μ-CT) were compared to those obtained by the Archimedes method. The latter indicated a relative density as high as 99.26%. Possible origins of porosity are discussed. The as-deposited material was comprised of both equiaxed and columnar grains with no preferred crystallographic orientation and mean grain size of 36 μm. The Young's modulus, yield stress, ultimate tensile strength, fracture strain, Poisson's ratio, and total ultimate strain energy (toughness) were determined by uniaxial tensile tests combined with digital image correlation (DIC). Fractography complemented the mechanical testing. A pulse-echo ultrasonic non-destructive test was used to obtain more accurate values of the Young's and shear moduli and to adjust the value of the yield strength accordingly. The measured mechanical properties meet the requirements of international standards for wrought Al 5754 in its annealed condition.
关键词： Additive manufacturing (AM),Mechanical properties,Micro-computed tomography (μ-CT),Laser Engineered Net Shaping (LENS?),Directed energy deposition (DED),Aluminum alloys
更新于2025-09-23 15:21:01
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Role of Sb on the vertical-alignment of type-II strain-coupled InAs/GaAsSb multi quantum dots structures
摘要： The implementation of GaAs0.8Sb0.2 as CL to obtain type-II strain-coupled InAs MQD structures has been examined and compared to similar structures without Sb or without strain coupling. First, it has been demonstrated that capping with GaAsSb prevents the formation of In-rich agglomerations that hampered the QD formation as it has been observed in the sample without Sb. Instead, it promotes the vertical alignment (VA) of almost all QDs with a high density of QD columns. Second, there is a preferential Sb accumulation over the dots together with an undulation of the growth front, contrary to the observed in the uncoupled structure. In case of a deficient covering of GaAsSb, as occurs for giant QDs, In-rich agglomerations may develop. Each VAQD column consists of a sequence of alternating quantum blocks of pyramid-shaped In(Ga)As separated by GaAsSb blocks that rest over them. These Sb-rich blocks are not homogeneous accumulating around the pyramidal apex like a collar. Between the columns, there is an impoverishment of In and Sb compared to the uncoupled sample. These columns can behave as self-aligned nanowires with type II band alignment between self-assembled InAs and GaAsSb quantum blocks that opens new opportunities for novel devices.
关键词： GaAsSb capping layer,III-V semiconductors alloys,Transmission electron microscopy,Composition distribution,Vertical aligned quantum dots
更新于2025-09-23 15:21:01
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Effects of oxygen pressure on PLD-grown Be and Cd co-substituted ZnO alloy films for ultraviolet photodetectors
摘要： We report on the synthesis of Be and Cd co-substituted ZnO (BexCdyZn1?x?yO) quaternary alloy films on c-plane sapphire substrates by pulsed laser deposition. The results show that all deposited films exhibit single-phase wurtzite structure with a surface roughness less than 1.5 nm. By adjusting the O2 pressure during growth, the optical bandgap of the film is tuned from ~3.3 to ~3.52 eV. At 5 V bias, the BexCdyZn1-x-yO-based photodetector exhibits a remarkable photoresponse in the ultraviolet region with low dark current (~ 16.2 pA) and high detectivity (9.31· 1010 Jones). The rise and decay times of the photodetectors based on BexCdyZn1-x-yO (order of seconds) are clearly faster than those based on pure ZnO (order of minutes). Higher O2 pressure results in better crystalline quality of BexCdyZn1-x-yO film and thus lower dark current and faster photoresponse in the device due to the decrease of oxygen vacancy-related defects under oxygen-rich growth conditions. These results indicate that oxygen pressure plays an important role in the growth of high-quality BexCdyZn1-x-yO alloy films, which have great potential in fabricating high-performance ultraviolet photodetectors.
关键词： Bandgap engineering,BexCdyZn1-x-yO alloys,UV photodetectors,Pulsed laser deposition
更新于2025-09-23 15:21:01
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One-step fabrication of trimetallic alloy nanozyme catalyzer for luminol-H2O2 chemiluminescence and its application for miRNA-21 detection coupled with miRNA walking machine
摘要： PtCuCo trimetallic alloys (PtCuCo-TAs) are synthesized by one-step reduction. The chemiluminescence (CL) properties of PtCuCo-TAs are studied systemically. PtCuCo-TAs show good catalyzing for luminol-H2O2 system. A CL platform is developed for the detection of miRNA-21 using PtCuCo-TAs as nanozyme catalyzer. In the CL detection platform, H1 (Hairpin DNA1) is immobilized onto magnetic beads (MBs) firstly. In the presence of miRNA-21, H1 is opened. H2 (Hairpin DNA2) then hybridizes with H1. Meanwhile, a "cleat" in the end of miRNA-21 with a fewer bases complementary is formed to prevent miRNA-21 dissociating from H1. This miRNA-21 hybridizes to another H1. When cpDNA-PtCuCo-TAs which consisted with cDNA (Complementary strand of probe DNA) and pDNA-PtCuCo-TAs (PtCuCo-TAs labeled with probe DNA) are added, the ssDNA region of H1 reacts with the toehold domain of probe DNA and cDNA is released resulting pDNA-PtCuCo-TAs being captured. With this process repeatedly, a lot of pDNA-PtCuCo-TAs are captured onto MBs. After separation and washing, the precipitate and H2O2 are put into the 96-well and luminol solution is injected. The CL signal is produced by PtCuCo-TAs catalyzing luminol-H2O2 system. The amount of miRNA-21 is detected with CL signal. This CL platform performs with limit of detection 0.167 fM and has good selectivity over other RNA.
关键词： Enzyme-free,miRNA-21,Nanocatalyst,One-step,Trimetallic alloys
更新于2025-09-23 15:21:01
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Microstructure of a Tia??50??wt% Ta alloy produced via laser powder bed fusion
摘要： Ti–Ta alloys have been widely studied for biomedical applications due to their high biocompatibility and corrosion resistance. In this work, nearly fully dense and in situ alloyed Ti–50 wt% Ta samples were fabricated by the laser powder bed fusion (LPBF) of mechanically mixed powders. With increased exposure time, and thereby increased laser energy density, insoluble Ta particles were almost dissolved, and a Ti–50 wt% Ta alloy was formed. Cellular and dendritic structures were formed due to constitutional undercooling, which was caused by the high cooling rate of LPBF process. Both retained β phases and α″ phases were observed in the LPBFed Ti–50 wt% Ta alloy. The α″ phase was found at the boundary of the cellular structures, where the tantalum content was not high enough to suppress the bcc lattice transition completely but could suppress the β phase → α′ phase transition.
关键词： Cellular and dendritic structures,Phase transformation,Ti–Ta alloys,Laser powder bed fusion,Microsegregation
更新于2025-09-23 15:21:01
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The relation between magnesium evaporation and laser absorption and weld penetration in pulsed laser welding of aluminum alloys: Experimental and numerical investigations
摘要： It is observed that in laser welding of aluminum alloys, magnesium can evaporate, and the weld penetration is dependent on Mg content of the alloy and Mg loss from the weld pool. In this research, it is proposed that the presence of Mg not in the base metal alloy, but rather the presence of Mg vapor in the plasma plume over the weld pool affects the laser absorption, and it is through this phenomenon that the weld profile and penetration is affected. Numerical simulation was performed to determine the relationship between the weld profile to estimate the effective laser absorption coefficient of four Al alloys and in parallel EPMA technique was used to determine the Mg losses of the weld metals. The combined analysis of the results showed that increasing the laser pulse energy (decreasing laser pulse frequency), Mg evaporation is increased, and that, in turn, increased the effective laser absorption coefficient. However, more laser power absorption does not necessarily mean more weld penetration. Laser absorption results in weld penetration, once the threshold Mg evaporation rate of 200 × ?10 6g/cm2 is passed.
关键词： Pulsed laser welding,Effective absorption coefficient,Aluminum alloys,Evaporation,Magnesium content,Penetration depth
更新于2025-09-23 15:21:01
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Evaluation of GaAs solar cells grown under different conditions via hydride vapor phase epitaxy
摘要： In this study, we characterize the GaAs solar cells grown under di?erent conditions using a custom-built at-mospheric-pressure hydride vapor-phase epitaxy (HVPE) reactor. Under typical HVPE growth involving the decomposition of AsH3 to Asx, the growth rate is considerably dependent on the temperature and is limited to ~10 μm/h at a low deposition temperature of 660 °C because of the large kinetic barrier of 198 kJ/mol. Herein, we grow GaAs with a considerably lower kinetic barrier of 7 kJ/mol by suppressing the decomposition of AsH3 in the reactor. Further, we grew GaAs solar cells at an extremely high growth rate of 120 μm/h using uncracked AsH3. However, the open-circuit voltage (VOC) was reduced from 1.0 V for the cells grown at 8 μm/h under typical growth using Asx to 0.95 V for the cells grown at 120 μm/h using hydride-enhanced growth. The reduction in VOC was attributed to the modulation of both the doping pro?le and the abruptness of hetero-interfaces. A small amount of residual gases, which presents at the growth surface after the growth of the p-InGaP back surface ?eld layer, is prominently incorporated during the growth of the p-GaAs base layer upon hydride-enhanced growth due to the fast kinetics.
关键词： B3. Solar cells,A3. Hydride vapor phase epitaxy,B2. Semiconducting gallium arsenide,B1. Alloys
更新于2025-09-23 15:19:57
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Grain refinement in laser remelted Mg-3Nd-1Gd-0.5Zr alloy
摘要： Columnar grains are normally favoured with the high cooling rate and steep thermal gradient in laser-based additive manufacturing. Here, we demonstrate that ?ne, fully equiaxed grains can be achieved in Mg-3Nd-1Gd-0.5Zr (EV31) alloy by laser surface remelting. The grains in the melt pool are remarkably re?ned from 74 μm to 3.5 μm, which can be attributed to the growth restriction effect, i.e. the constitutional supercooling formed by Zr solute during solidi?cation in combination with the high cooling rate imposed by laser surface remelting. This novel ?nding could be applied for the control of grain morphology and alloy design for additive manufacturing applications.
关键词： Solidi?cation microstructure,Grain re?ning,Laser treatment,Magnesium alloys,Rapid solidi?cation
更新于2025-09-23 15:19:57
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First-principle study of g-AlxGa1-xN alloys: planar and buckled structures
摘要： The fundamental properties of g-AlxGa1-xN alloys with planar and buckled structures are investigated based on the first-principles. The results show that the band gaps of g-AlxGa1-xN alloys can be tuned, making them promising candidate materials for future light-emitting applications. For two-dimensional planar single layer structures, the band gap of g-AlxGa1-xN alloy increase monotonically with the increase of Al concentration. In contrast, for the buckled structures, as Al concentration increases, the band gap of the alloy structure first increase and then decrease, for the Al0.5Ga0.5N alloy, maximum band gap values can be achieved. The ε peaks and absorption coefficients of planar structures blue-shift, but those of the buckled structures red-shift. The absorption coefficients of the two type structures show two distinct absorption peaks in the deep ultraviolet, therefore deep ultraviolet emission is considered to be a remarkable feature of g-AlxGa1-xN alloys, indicating the potential use of g-AlxGa1-xN alloys for future UV luminescence applications.
关键词： g-AlxGa1-xN alloys,Electronic structure,Optical properties,Two-dimensional material,The first principles
更新于2025-09-23 15:19:57
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Phasea??Controlled Synthesis of Monolayer W <sub/>1a??</sub><i> <sub/>x</sub></i> Re <i> <sub/>x</sub></i> S <sub/>2</sub> Alloy with Improved Photoresponse Performance
摘要： Tuning bandgap and phases in the ternary 2D transition metal dichalcogenides (TMDs) alloys has opened up unexpected opportunities to engineer optoelectronic properties and explore potential applications. In this work, a salt-assisted chemical deposition vapor (CVD) growth strategy is reported for the creation of high-quality monolayer W1?xRexS2 alloys to fulfill a readily phase control from 1H to DT by changing the ratio of Re and W precursors. The structures and chemical compositions of doping alloys are confirmed by combining atomic resolution scanning transmission electron microscopy-annular dark field imaging with energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy, matching well with the calculated results. The field-effect transistors (FETs) devices fabricated based on 1H-W0.9Re0.1S2 monolayer exhibit a n-type semiconducting behavior with the mobility of 0.4 cm2 V?1 s?1. More importantly, the FETs show high-performance responsivity with a value of 17 μA W?1 in air, which is superior to that of monolayer CVD-grown WS2. This work paves the way toward synthesizing monolayer ternary alloys with controlled phases for potential optoelectronic applications.
关键词： W1?xRexS2 alloys,phase transition,ternary TMDs,chemical vapor deposition,photoresponsivity
更新于2025-09-23 15:19:57