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Mechanism of Liquid-Phase Reductive Thin-Film Deposition under Quasiballistic Electron Incidence
摘要： Highly reducing activity of quasiballistic hot electrons emitted from a nanocrystalline silicon (nc-Si) diode is veri?ed in terms of liquid-phase thin ?lm deposition. Incident electrons reduce positive ions in salt solutions coated on a target substrate, and then result in deposition of thin metal (Cu) and semiconducting (Si, Ge, and SiGe) ?lms. This mechanism is investigated here throughout the process from electron incidence to thin ?lm deposition. Thermodynamic criterion deduced from classical nucleation theory suggests that the output electron energy of the nc-Si emitter is suitable for promoting preferential reduction of target ions in solutions leading to the nuclei formation. In accordance with mass-transport analyses on generated nanoclusters, the most primary factor of thin ?lm growth is the dose of incident electron. The formulated deposition rate rapidly increases and reaches a stationary value within 0.1 s after electron incidence. The theoretical dependency of the thin ?lm thickness on the electron incidence time is consistent with the experimental results. Speci?c features of this scheme as an alternative approach for thin ?lm deposition are discussed in comparison with the conventional dry and wet processes.
关键词： nanocrystalline silicon diode,quasiballistic hot electrons,mass-transport analyses,thermodynamic criterion,liquid-phase thin film deposition
更新于2025-09-23 15:21:21
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Dynamic Interplay between Transport and Reaction Kinetics of Luminophores on the Operation of AC-driven Electrochemiluminescence Devices
摘要： Electrochemiluminescence (ECL) involves light emission accompanied by a series of electrochemical processes on luminophores, which has been recently exploited in a new light-emitting device platform, referred to as the ECL device (ECLD). Here, we investigate the influence of the transport of the ECL luminophores and their reaction kinetics on the emission properties of AC-voltage-driven ECLDs. A model based on the diffusion and reaction rate equations is developed to predict the operational frequency (f)-dependent luminance properties of the ECLD. It is found that more frequent generation of the redox precursors with a shorter time interval enhances their probability of encountering each other, and therefore, the luminance of the device increases with increasing f initially. The luminance at a higher f, however, is suppressed eventually due to the decreased rate of the electrode reactions. Using the model, the influence of diffusion and reaction rates on the performance of an ECLD is analyzed separately and systematically. The results provide insight on the operation of this emerging class of light-emitting device platform.
关键词： electrochemiluminescence,ionic transition metal complex,reaction kinetics,mass transport,ionic liquid,light-emitting device
更新于2025-09-23 15:21:01
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A UV‐LEDs based photomicroreactor for mechanistic insights and kinetic studies in the norbornadiene photoisomerization
摘要： In this work, we report a simple and inexpensive UV-LEDs based photomicroreactor assembly constructed by commercially available components. The photoisomerization of norbornadiene to quadricyclane was selected to validate this novel photomicroreactor design. Mass transport limitation was eliminated and indicated by dimensionless numbers Fo and DaII, and photons loss was evaluated considering the absorption and reflection of the microreactor walls. The solvents, photosensitizers and light sources selections were optimized for achieving better photochemical performance and mechanistic insights. The detailed comparison between the high-pressure mercury arc lamp and the UV-LEDs strip revealed great potential of UV-LEDs as appealing light source for photochemical transformations. Moreover, the reaction mechanism was thoroughly discussed and illustrated by the Jablonski diagram indicating electronic states transitions. According to possible intermediate steps, a kinetic model was proposed with the reaction rate constant being correlated with the photon flux, which is valuable for process optimization and further understanding reaction mechanisms.
关键词： photosensitization,reaction kinetics,microreactor,mass transport,UV-LED
更新于2025-09-19 17:13:59
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Numerical modelling of heat transfer, mass transport and microstructure formation in a high deposition rate laser directed energy deposition process
摘要： In laser directed energy deposition (L-DED) processes, by applying a converged powder stream, relatively high laser power and larger laser spot, the powder utilisation efficiency and processing speed can be increased. There is, however, lack of mathematical models for L-DED. In this paper, a three-dimensional numerical model is established to study the mass transport and heat transfer in the melt pools in high deposition rate (HDR) L-DED of 316L stainless steel. The Volume of Fluid (VOF) method is employed to track the melt pool free surfaces, and enthalpy-porosity method is used to model the solid-liquid phase change. A discrete powder source model is developed by considering the non-uniform powder feed rate distribution. Results show that this model can well predict the deposited track dimensions (width, height and dilution depth). Different from conventional L-DED processes, the impact of higher mass addition on the melt pool fluid flow and temperature distribution is significant. In the regions where filler powder is injected, a downward mass flow is observed, and the temperature is slightly reduced. With the extracted temperature distribution and geometry at the solidification front, the solidification conditions are also calculated, as well as the primary dendrite arm spacing (PDAS) of the solidified tracks. Due to the high laser energy input, the temperature gradient is lower, and coarser microstructures are formed compared with conventional L-DED. The simulated results are in good agreement with experimental results.
关键词： Heat transfer,High deposition rate laser directed energy deposition,Mass transport,Primary dendrite arm spacing
更新于2025-09-19 17:13:59
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High Sensitivity Detection of Copper Ions in Oysters Based on the Fluorescence Property of Cadmium Selenide Quantum Dots
摘要： Enhancing the mass transport from the flow field side to the membrane side without sacrificing the active surface area is a critical strategy for the design of electrodes in flow-field structured vanadium redox flow batteries (VRFBs). In this work, we design and prepare a novel porous electrode with a gradient distribution in pores, enabling a gradual decrease in permeability but an increase in active surface areas from the flow field side to the membrane side. This design not only increases the electrode utilization due to the enhanced mass transport near the flow field side, but also avoids the loss of active surface area near the membrane side. Numerical modeling results show that compared to the conventional electrode design, the gradient electrode design can promote the uniform distribution of local reaction current density and overpotential, leading to a lower charge voltage and higher discharge voltage. Experimental results show that at the current density of 240 mA cm?2, the battery with the gradient electrode design delivers a 69% higher discharge capacity than that with the conventional electrode design, demonstrating the superiority of the gradient electrode design strategy.
关键词： Gradient porous electrode,Large-scale energy storage,Mass transport,Vanadium redox flow batteries
更新于2025-09-11 14:15:04
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Sensitive Bacterial Detection via Dielectrophoretic Enhanced Mass Transport Using Surface Plasmon Resonance Biosensors
摘要： The performance of surface plasmon resonance (SPR)-based bacterial biosensors is often compromised due to diffusion-limited mass transport of bacteria to the sensing surface. In this work, dually functional interdigitated electrodes (IDEs) were developed to sustain SPR, and increase bacterial mass transport through external application of dielectrophoresis (DEP). IDEs were defined into 50 nm thick Au films with fixed electrode gaps (EG = 5 μm) and varied electrode widths (EW = 10, 20, and 100 μm), and referred to as interdigitated SPR (iSPR) chips. The iSPR chips with EW = 100 μm can effectively support SPR, with comparable sensitivity to the conventional SPR chips. The surfaces of iSPR chips (EW = 100 μm) were modified with mannose to target the FimH adhesin of E. coli and increase cellular adhesion. An LOD of ~3.0 x 102 CFU/mL E. coli was achieved on mannosylated iSPR chips under pDEP condition, which is about five orders of magnitude improvement compared to the mannosylated conventional SPR chips without DEP. Furthermore, secondary antibody amplification enabled selective enhancement of dilute (103 CFU/mL), E. coli suspensions, while no amplification was observed for concentrated (108 CFU/mL), non-target (S. epidermidis) bacterial suspensions. The results presented here indicate a great potential of the incorporation of DEP into SPR biosensors for rapid, sensitive, and specific detection of bacteria with broad applications in the areas of biomedical diagnostics, environmental monitoring, food safety, and homeland security.
关键词： bacterial detection,dielectrophoresis,surface plasmon resonance,mass transport,biosensors
更新于2025-09-10 09:29:36
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Preparation of TiO2 Microspheres with Tunable Pore and Chamber Size for Fast Gaseous Diffusion in Photoreduction of CO2 under Simulated Sunlight
摘要： TiO2 microsphere with tunable pore and chamber size are prepared by a simple solventhermal method and used as catalyst for the photocatalytic CO2 reduction. It is found that the hollow microsphere with relative lower surface area of 73.8 m2g-1 exhibits increased pore size of 18.1 nm and cavity structure, leading to higher CO2 diffusion coefficient of 5.40×10-5 cm2s-1 compared with the solid and yolk/shell microspheres. Therefore, the hollow microsphere possesses more accessible sites for CO2 adsorption, which finally gives rise to the enhanced CO production rate of 10.9±0.7 μmolg-1h-1 under simulated sunlight, which is respectively 1.6 and 1.4 times higher than that of solid and yolk/shell microspheres. Electron dynamic study further demonstrates that hollow microsphere shows the highest photocurrent density and the lowest charge recombination among three microspheres structure, which is attributed to the swift CO2 diffusion providing fresh CO2 molecules to rapidly scavenge the photo-generated electrons and finally leading to the excellence catalytic reduction performances. This method could be adopted as a general strategy to prepare high performance TiO2 catalysts with desirable structural qualities for the photocatalytic CO2 reduction under nature sunlight.
关键词： TiO2,CO2 reduction,Hollow structures,Photocatalysis,Mass transport
更新于2025-09-04 15:30:14