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Pulsed laser deposited Cr-doped CoFe2O4 thin film as highly efficient oxygen evolution reaction electrode
摘要： Traditional powder OER catalysts have many disadvantages such as the extremely complicated electrode preparation process. Herein, squama-like Co0.95Cr0.05Fe2O4 thin film electrode is directly deposited on flexible Ni foam substrate by a novel method of pulsed laser deposition. Cr doping leads to the electrode highly effective for OER, and the current density is about 2.1 times of that compared with undoped CoFe2O4 thin film at 1.8 V. The Co0.95Cr0.05Fe2O4 thin film exhibits an overpotential of 293.3 mV at 10 mA/cm2 as well as extraordinary stability, which is far better than that of CoFe2O4 thin film and no-load Ni foam.
关键词： Thin films,Pulsed laser deposition,Electron microscopy,Oxygen evolution reaction
更新于2025-09-12 10:27:22
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MoSx quantum dots modified black silicon for high efficient photoelectrochemical hydrogen evolution
摘要： Nanostructured black silicon (bSi) is widely used for solar water splitting application due to the excellent light-harvesting properties and large surface area-to-volume ratio that favors photoelectrochemical reactions. However, bSi suffers from low catalytic activity, owing to its poor charge transfer kinetics during hydrogen evolution process. In this work, we developed a novel photoelectrode by incorporating molybdenum sulfide (MoSx) quantum dots on the surface of black silicon. The synergetic effect of MoSx and bSi significantly enhance the activity for hydrogen evolution reaction. An onset potential of 0.255 VRHE, a high short-circuit photocurrent density (Jsc) of 12.2 mA·cm-2, and a hydrogen evolution rate of 226.5 μmol·h-1·cm-2 have been achieved.
关键词： photocathode,Black silicon,MoSx quantum dots,hydrogen evolution reaction
更新于2025-09-12 10:27:22
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Transport phenomena and keyhole evolution process in laser welding of stainless steel; 激光焊接不锈钢过程中输运现象和小孔演化;
摘要： Knowledge of transport phenomena and keyhole evolution is important for controlling laser welding process. However, it is still not well understood by far due to the complex phenomena occurring in a wide temperature range. A transient 3D model including heat transfer, fluid flow and tracking of free surface is built in this study. The transport phenomena are investigated by calculating the temperature and velocity fields. The 3D dynamic keyhole evolution process is revealed through tracking free surface using volume-of-fluid method. The results show that the keyhole deepening speed decreases with laser welding process before the quasi-steady state is reached. The plasma can greatly affect the keyhole depth through absorbing a great amount of laser energy and thus lowering the recoil pressure. Moreover, the relationship between keyhole depth and weld penetration is also discussed. This paper can help to better understand the dynamics in molten pool and then improve laser welding process.
关键词： weld penetration,keyhole evolution,laser welding,weld pool dynamics,free surface tracking
更新于2025-09-12 10:27:22
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Structure–Activity/Stability Correlations from the Electrochemical Dynamic Responses of Titanium Anode Coatings Formed of Ordered TiO <sub/>2</sub> @RuO <sub/>2</sub> Microspheres
摘要： Spherical TiO2/RuO2 particles were synthesized by ultrasonic spray pyrolysis (USP) at 200 and 800?C. The activity for the oxygen and chlorine evolution reactions (OER and CER, respectively) and the dynamic responses from electrochemical impedance spectroscopy (EIS) of the USP powders, as well as of the corresponding coatings on Ti, were analyzed and are discussed. The loss of coating activity is discussed with respect to the differences in the EIS and cyclic voltammetry responses of the coatings in their active and inactive states. The 800?C-USP sample was found to be more active than the 200?C-USP sample for both the CER and the OER, whereas the stability of the former was considerably lower. The correlation between the structure, composition and morphology of the powder and the coating with the registered electrochemical properties is discussed. The EIS analysis of the coating resistance distributions induced by the thermal treatment of the powder indicated a complex combination of the pore resistance and the pseudocapacitive charge transfer resistance. An additional coating resistance, due to loose grain boundaries, was introduced into the coatings in their active and inactive state. The EIS analysis indicated the changes in TiO2-enriched core/RuO2-enriched shell structure, caused by the USP temperature.
关键词： TiO2/RuO2,cyclic voltammetry,electrochemical impedance spectroscopy,oxygen evolution reaction,chlorine evolution reaction,ultrasonic spray pyrolysis,coating stability
更新于2025-09-11 14:15:04
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Controlled Micro/Nanodome Formation in Proton‐Irradiated Bulk Transition‐Metal Dichalcogenides
摘要： At the few-atom-thick limit, transition-metal dichalcogenides (TMDs) exhibit strongly interconnected structural and optoelectronic properties. The possibility to tailor the latter by controlling the former is expected to have a great impact on applied and fundamental research. As shown here, proton irradiation deeply affects the surface morphology of bulk TMD crystals. Protons penetrate the top layer, resulting in the production and progressive accumulation of molecular hydrogen in the first interlayer region. This leads to the blistering of one-monolayer thick domes, which stud the crystal surface and locally turn the dark bulk material into an efficient light emitter. The domes are stable (>2-year lifetime) and robust, and host strong, complex strain fields. Lithographic techniques provide a means to engineer the formation process so that the domes can be produced with well-ordered positions and sizes tunable from the nanometer to the micrometer scale, with important prospects for so far unattainable applications.
关键词： transition-metal dichalcogenides,hydrogen evolution reaction,strain,photoluminescence,2D materials,Raman
更新于2025-09-11 14:15:04
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A photocounting distribution formula for a laser channel
摘要： For a laser channel governed by the master equation of the density operator which involves both photon gain and loss parameters, g and κ, we derive a new formula for the photocount distribution at time t for an initial density operator ρ0. The formula brings convenience, since we need not derive the density operator ρt at time t. Moreover, this formula is applied to the case of a damping channel and a di?usion channel, respectively.
关键词： Photocount distribution,Damping channel,Evolution law,Di?usion channel,Laser channel
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Optical Soliton Molecular Complexes in Ultrafast Fiber Lasers
摘要： Optical soliton molecules are under intense research focus, owing in particular to the interesting analogies between their self-assembly and internal dynamics, and those of matter molecules. Two interacting dissipative solitons can form a soliton-pair molecule, which can behave as a robust entity traveling around the cavity for an indefinite time [1]. The internal oscillatory dynamics of soliton molecules can be compared to molecular vibrations, though they are fundamentally different [2,3]. The recent experimental investigations in Refs. [2,3] have been enabled by the dispersive Fourier transform (DFT) technique, which allows recording spectral measurements at multi-MHz frame rates. They showed the existence of various oscillatory dynamics among soliton-pair and soliton-triplet basic molecules. Following the analogy between light and matter molecules, we now consider the experimental possibility of forming a “soliton molecular complex” (SMC), namely, a higher-order pattern obtained by the stable bonding of several soliton molecules, and investigating its complex internal dynamics. Such structure implies two different bond types, a strong one within each soliton molecule, and a weaker one to maintain the overall structure. We here report the first real-time recording and analysis of several internal dynamics of SMCs, which support this new structural concept. We shall describe our results concerning the dynamics of the fundamental SMC, made of two soliton-pair molecules, or (2+2)-SMC. The experimental configuration is based on an erbium-doped fiber ring laser, which is mode-locked by means of nonlinear polarization evolution (NPE), and its output spectrum analyzed in real-time through DFT [4]. The formation of various SMC is controlled by the laser output power and the tuning of NPE through the orientation of intracavity waveplates, in an experimental procedure which utilizes the hysteretic laser behavior in the multi-pulse regime. SMCs with sliding-phase and oscillating-phase dynamics have been characterized by real-time spectral interferometry measurements, thus revealing the dynamics of the major internal degrees of freedom of the complexes, namely the dynamics of the relative temporal and phase separations between the different soliton constituents. Numerical simulations confirm the experimental observations and offer an additional insight into the understanding of the complex dynamics of SMCs. By showing that soliton molecules can form various bonds according to the distance between soliton constituents, which we can manipulate, this work opens the way to the manipulation of large-scale optical- soliton complexes, which can be extended to other photonic platforms, such as microresonators.
关键词： soliton molecular complex,Optical soliton molecules,nonlinear polarization evolution,ultrafast fiber lasers,dispersive Fourier transform
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Comparison of Different Mode-Locking Methods in the Ho-Doped Fiber Laser
摘要： Ultrafast fiber sources operating in the spectral range of 2-3 μm have attracted attention due to a number of possible applications, e.g. for perspective communications, gas sensing, nonlinear frequency conversion, and medicine. Holmium-doped fibers (HDF) are commonly used as a gain medium for 2 μm lasers due to their broad gain spectrum, extending from 2 to 2.2 μm. Most of the presented works on Ho-doped ultrafast fiber lasers have concentrated on mode-locking regime initiated by saturable absorbers (SAs) such as carbon nanotubes (CNT) [1], graphene [2], black phosphorus [3], and semiconductor saturable absorber mirrors (SESAMs) [4]. The mode-locking regime in an all-fiber Holmium laser also has been obtained by nonlinear polarization evolution (NPE) [5]. In this work, we demonstrate a comparison of different methods of mode-locking obtaining in one Ho-doped fiber laser cavity under the same condition and analyze the parameters of the obtained pulsed radiation. We have compared such methods as NPE and two hybrid regimes: NPE+single walled CNTs [6, 7], NPE+graphene. The optical scheme of the experimental setup is shown in Fig. 1. Ho-doped fiber laser was pumped through a wavelength division multiplexer (WDM) by a custom-made 1125 nm Yb-doped fiber laser delivering up to 8 W of continuous wave power. The cavity of the laser was formed by active Ho-doped fiber (≈ 6 m) and single-mode fiber (≈ 8 m). A fiber polarizer and a pair of polarization controllers were added into the laser cavity to obtain NPE mode-locking. The SWCNTs or graphene SA were fixed between two optical FC/APC-connectors to realize hybrid mode-locking. The isolator (ISO) was used to obtain unidirectional lasing. The pulse signal was coupled out from the laser cavity using a 9/1 fiber coupler (90% coupler output was used as the output of the laser). The total intracavity dispersion was estimated as about –1.5 ps2. Stable pulsed lasing by NPE was obtained at a pump power of 3 W, whereas in the case of NPE+SWCNTs mode-locking lasing threshold increased up to 3.3 W of pump power. The average lasing power in the NPE and NPE+SWCNTs regimes was 6.4 and 4.7 mW, respectively. Fig. 2 shows the emission spectra of a pulsed Ho-doped fiber laser operating in different regimes. As can be seen, the spectra have different values of the central wavelength and full width at half maximum (FWHM). Fig. 3 shows the autocorrelation traces. The pulse width in both cases did not exceed 1.5 ps. The pulse energies in the NPE mode-locking and NPE+SWCNTs mode-locking regimes were 0.4 and 0.3 nJ, respectively. The pulse repetition frequency was 14.9 MHz. The signal-to-noise ratio in the case of NPE+SWCNTs mode-locking was 3 dB better than that implemented under conditions of NPE mode-locking.
关键词： saturable absorbers,mode-locking,hybrid regimes,Ho-doped fiber laser,nonlinear polarization evolution
更新于2025-09-11 14:15:04
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The effect of different scanning strategies on microstructural evolution to 24CrNiMo alloy steel during direct laser deposition
摘要： 24CrNiMo alloy steel is a low-alloy high strength steel and was used to fabricate engine components and brake discs. In the current study, Direct Laser Deposition (DLD) was used to additively manufacture 24CrNiMo alloy steel samples with high strength and ductility. The microstructural evolution, texture and mechanical properties of deposited samples can be affected by changing inter-layer time intervals and scanning strategy between deposited layers. The granular bainite (GB) and lath martensite (LM) inside deposited samples were obtained by inter-layer successive deposition and 2-minute intervals deposition, respectively, because of the different cooling rates of different inter-layer time intervals. The occurrence of 2-minute intervals between cladding layers leads to higher cooling rates, resulting in finer grain size. In addition, the relatively strong textures could be transformed into the weak ones since the columnar dendrites were fragmented by the different heat transfer directions resulting from a scanning strategy of 90°-rotation between cladding layers. Less inclusions and un-melted powders inside deposited samples were obtained when a scanning strategy of 90°-rotation between deposited layers was applied. The experimental results indicate that a deposited sample with excellent tensile properties and microhardness was fabricated by an optimized laser scanning strategy. The optimized scanning strategy mainly include inter-layer 2-minute intervals and 90°-rotation between deposited layers. Deposited samples fabricated by the optimized scanning strategy have comparable tensile strength and ductility to those of other forged low-alloy high strength steel. Therefore, this optimized laser scanning strategy can be applied to manufacture low-alloy steel with high tensile properties.
关键词： microstructural evolution,scanning strategy,direct laser deposition,mechanical properties,24CrNiMo alloy steel
更新于2025-09-11 14:15:04
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Hybrid 0D/2D Ni2P quantum dot loaded TiO2(B) nanosheet photothermal catalysts for enhanced hydrogen evolution
摘要： The development of low cost, stable, robust photocatalysts to convert solar energy into hydrogen energy is an important challenge. Here, we describe a simple solvothermal method to successfully fabricate a catalyst with a hybrid 0D/2D Ni2P quantum dot/TiO2(B) nanosheet architecture. HRTEM shows that Ni2P quantum dots about 5 nm in size were dispersed on ultrathin TiO2(B) nanosheets. The optimum photocatalytic H2 evolution rate with 10 wt% Ni2P/TiO2(B) (3.966 mmol g?1 h?1), which was 15 times higher than pure TiO2(B) nanosheets. Significantly, the new catalyst shows high stability and reusability in multiply cycled H2 production runs for a 30 h period. The H2 production rate can be considerably increased furthered by using synergistic photothermal H2 evolution (20.129 mmol g?1 h?1 at 90 °C).
关键词： TiO2(B) nanosheets,Photocatalytic H2 evolution,Ni2P quantum dots,0D/2D architecture,Synergistic photothermal catalysis
更新于2025-09-11 14:15:04