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Advanced Silicon Carbide Devices and Processing || Investigation of SiC/Oxide Interface Structures by Spectroscopic Ellipsometry
摘要： We have investigated SiC/oxide interface structures by the use of spectroscopic ellipsometry. The depth profile of the optical constants of thermally grown oxide layers on SiC was obtained by observing the slope-shaped oxide layers, and the results suggest the existence of the interface layers, around 1 nm in thickness, having high refractive index than those of both SiC and SiO2. The wavelength dispersions of optical constants of the interface layers were measured in the range of visible to deep UV spectral region, and we found the interface layers have similar dispersion to that of SiC, though the refractive indices are around 1 larger than SiC, which suggests the interface layers are neither transition layers nor roughness layers, but modified SiC, e.g., strained and/or modified composition. By the use of an in-situ ellipsometer, real-time observation of SiC oxidation was performed, and the growth rate enhancement was found in the thin thickness regime as in the case of Si oxidation, which cannot be explained by the Deal-Grove model proposed for Si oxidation. From the measurements of the oxidation temperature and oxygen partial pressure dependences of oxidation rate in the initial stage of oxidation, we have discussed the interface structures and their formation mechanisms within the framework of the interfacial Si-C emission model we proposed for SiC oxidation mechanism.
关键词： interface state density,SiC-MOSFET,SiC/oxide interface,SiC oxidation mechanism,spectroscopic ellipsometry
更新于2025-09-23 15:22:29
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Metal-Organic Frameworks Derived from Zero-Valent Metal Substrates: Mechanisms of Formation and Modulation of Properties
摘要： The replicative construction of metal–organic frameworks (MOFs) templated with solvent-insoluble solid substrates is of marked importance, as it allows for the assembly of 2D and 3D macro- and mesoscopic architectures with properties that are challenging to attain by the conventional solution-based synthesis approach. This work reports an in situ and direct construction of MOFs from zero-valent metal substrates via a green hydrothermal oxidation–MOF construction chemistry without the use of any additional metal source, chemical reagents, or acidification of solvent, and elucidates the zero-valent metal derived formation mechanisms of MOFs and their structure modulation to 1D nanofibers (NFs), 2D film, and 3D core–shell microstructures. Through modulation of the competing surface oxidation-dissolution and MOF crystallization kinetics, Al@MIL-53 core–shell microstructures and MIL-53 (Al) NFs are obtained that exhibit unique morphologies and marked properties superior to the conventional MIL-53 (Al) powders. The generality of zero-valent metal-templated synthesis of MOFs is demonstrated with formation of MIL-53 (Al), HKUST-1, and ZIF-7 polycrystalline films on Al, Cu, and Zn metal meshes, elucidating the significance of the approach utilizing solid metal substrate that can be easily processed into various shapes, architectures, and compositions.
关键词： MOF nanofibers,formation mechanism,core–shell structure,templated synthesis,metal–organic framework
更新于2025-09-23 15:22:29
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A micro-structural corrosion mechanism on the thermal degradation of BaMgAl10O17: Eu2+ phosphor
摘要： The thermal degradation is a vital issue that restricting luminous efficiency and service life of BaMgAl10O17: Eu2+phosphor for chromogenic and illuminating fields. The effects of heat-treatment temperature on the luminescence properties and micro-structure of BAM were researched to accurately elucidate the thermal degradation mechanism. Some pieces of evidence for micro-structural corrosion were detected according to the results of PL, TL, XPS and IR. With the heat-treatment temperature increasing, a decrease of blue-emitting intensity and new red-emitting peaks revealed thermal degradation and activator oxidation. The XPS results showed the surface chemical composition changes and the micro-structure adjustment. The defects elimination detected by TL could be responsible for this micro-structural corrosion. IR results further confirmed the changes on bond forms. These were direct evidence and specific forms for the micro-structural corrosion due to the thermal degradation. Based on the relationship between micro-structural corrosion and luminescence properties, a micro-structural corrosion mechanism was given for the thermal degradation of BAM phosphor. The thermal degradation was caused in parallel by the micro-structure corrosion and the activated ion (Eu2+) oxidation.
关键词： Micro-structural corrosion,Thermal degradation mechanism,BaMgAl10O17:Eu2+,Heat-treatment
更新于2025-09-23 15:22:29
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Synergetic utilization of photoabsorption and surface facet in crystalline/amorphous contacted BiOCl-Bi2S3 composite for photocatalytic degradation
摘要： Photoabsorption and surface property of semiconductor are two key factors to determine its photocatalytic performance. In this work, BiOCl-Bi2S3 composites composed of Bi2S3 nanoparticles bonded on BiOCl nanoplates enclosed with {001} and {110} crystal facets were synthesized through an in-situ ion exchange method at room temperature. The transformed Bi2S3 made BiOCl-Bi2S3 composites efficient visible light absorption, ensuring the quantity of photoinduced carriers as well as intimate crystalline-amorphous contact interface to benefit the separation of photoinduced carriers. Moreover, BiOCl nanoplates enclosed with {001} and {110} crystal facets can convenient transfer carriers to {001} crystal facets. The photocatalytic performance of BiOCl-Bi2S3 composites was evaluated by the methylene blue photodegradation under visible light irradiation and the results indicate that BiOCl-Bi2S3 composites have good photocatalytic ability due to enhanced light absorption, efficient separation and transfer of carriers. Based on the active species trapping experiments, transient photocurrents, electrochemical impedance spectroscopy and energy band structure, a possible photocatalytic mechanism of methylene blue over the BiOCl-Bi2S3 composites was proposed.
关键词： Surface property,Visible light,BiOCl-Bi2S3,Contact interface,Photocatalytic mechanism,Crystal facet
更新于2025-09-23 15:22:29
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Improved thermal stability of Y3Al5O12:Ce3+ phosphor by SiO2 coating
摘要： In this paper, a heterogeneous precipitation method was adopted to coat a SiO2 layer on the surface of Y3Al5O12:Ce3+ phosphor. The surface morphologies, crystal phases, defect concentrations, luminescent properties and thermal stability of coated phosphors were investigated and compared with those of uncoated phosphor. A compact and homogeneous SiO2 layer on the surface of phosphor was determined by SEM-EDS, TEM, XRD and FT-IR results. Two thermoluminescent peaks were found at 112 oC and 248 oC on the thermoluminescence spectrum. Their intensities decreased slowly with the increasing coating amounts. It indicated that their corresponding defect concentrations were gradually reduced. Improved thermal stability was obtained by SiO2 coating in spite of a slight weakening of the emission intensity. The optimum theoretical coating amount was identified as 4%. Moreover, a structural modification mechanism on improved thermal stability of SiO2 coated Y3Al5O12:Ce3+ was proposed.
关键词： Y3Al5O12:Ce3+ phosphor,thermal stability,coating,structural modification mechanism
更新于2025-09-23 15:22:29
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Synthesis of silver phosphate/sillenite bismuth ferrite/graphene oxide nanocomposite and its enhanced visible light photocatalytic mechanism
摘要： In the present work, silver phosphate/sillenite bismuth ferrite/graphene oxide (Ag3PO4/Bi25FeO40/GO) nanocomposite has been successfully fabricated via hydrothermal strategy and ultrasound precipitation treatment. Afterwards, physicochemical properties of as-obtained composite were studied through X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), Brunauer-Emmett-Teller (BET) surface areas, vibrating sample magnetometer(VSM) measurements. Meanwhile, Linear sweep voltammetry (LSV), Mott-Schottky (M-S), Transient photocurrent-curves and electrochemical impedance spectroscopy (EIS) measurements were measured to investigate the photoelectrochemical properties. Besides, the degradation efficiency of Rhodamine B was as the evaluation of PC efficiency, which could reach 96.9% after 75min illumination. The results indicated that spherical Ag3PO4 and Bi25FeO40 crystallographic particles were integrated with GO and the enhanced PC performance can be attributed to significantly visible light absorbance and charge separation efficiency. Furthermore, to distinguish the contribution of reactive species including ?O2?, ?OH, H2O2, h+ and e?, several scavenger experiments have been conducted. Noticeable, the Ag3PO4/Bi25FeO40/GO nanocomposite has magnetic because of the integration with Bi25FeO40. Eventually, the possible photocatalytic performance mechanism of Ag3PO4/Bi25FeO40/GO was proposed.
关键词： Ag3PO4/Bi25FeO40/GO,Visible light photocatalysis,Photocatalytic performance mechanism,Magnetic nanocomposite
更新于2025-09-23 15:22:29
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Copper Nanowire Dispersion through an Electrostatic Dispersion Mechanism for High-Performance Flexible Transparent Conducting Films and Optoelectronic Devices
摘要： Highly dispersed copper nanowire (CuNW) is an essential prerequisite for its practical application in various electronic devices. At present, the dispersion of CuNW is almost realized through the steric hindrance effect of polymers. However, the high post-treatment temperature of polymers makes this dispersion mechanism impractical for many actual applications. Here, after investigating the relationships between the electrostatic dispersion force and influence factors, an electrostatic dispersion mechanism is refined by us. Under the guidance of this mechanism, high dispersion of CuNW and a record low post-treatment temperature (80 ℃ ) are realized simultaneously. The high dispersity endows CuNW with good stability (–45.66 mV) in water-based ink, high uniformity (65.7 ± 2.5 Ω sq-1) in the prepared transparent conducting film (TCF) (23 cm × 23 cm) and industrial film-preparation process which are the issues that hinder the widespread application of CuNW-based TCF at present. The low post-treatment temperature makes CuNW possible for applying on any substrate. In addition, the charge modifier, 2-mercaptoethanol, enables CuNW to resist oxidation well. Finally, flexible optoelectronic devices employing the CuNW film as the electrode are fabricated and show efficiencies comparable to those of optoelectronic devices on ITO/glass.
关键词： copper nanowires,flexible optoelectronic devices,electrostatic dispersion mechanism,transparent conducting films,post-treatment temperatures
更新于2025-09-23 15:22:29
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Monometallic Catalytic Models Hosted in Stable Metal-Organic Frameworks for Tunable CO2 Photoreduction
摘要： The photocatalytic reduction of CO2 to energy carriers has emerged as one of the most promising strategy to alleviate the energy crisis and CO2 pollution, for which the development of catalyst was considered as the determining factor for the accomplishment of this conversion process. In this study, three stably and isostructural metal organic frameworks (denoted as MOF-Ni, MOF-Co and MOF-Cu), have been synthesized and used as heterogeneous catalysts applied into photocatalytic CO2 reduction reaction (CO2RR). It is worth noting that the MOF-Ni exhibited a very high selectivity of 97.7% for photoreducing CO2 to CO, which has exceeded most of the reported MOF-based catalysts in the field. Significantly, the MOFs associated with monometallic catalytic centre offer a simply and precisely structural model which allows us to understand the specific effects of different metal ion species on photoreduction of CO2 as well as reactive mechanism more intuitively.
关键词： Isostructural,Metal-Organic Frameworks,Photocatalytic CO2 Reduction,High Selectivity,Monometallic Catalytic Model,Reactive Mechanism
更新于2025-09-23 15:22:29
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Elucidating Spray Dried Dispersion Dissolution Mechanisms with Focused Beam Reflectance Measurement: Contribution of Polymer Chemistry and Particle Properties to Performance
摘要： Amorphous spray dried dispersions (SDDs) are a key enabling technology for oral solid dosage formulations, used to improve dissolution behaviour and clinical exposure of poorly-soluble active pharmaceutical ingredients (APIs). Appropriate assessment of amorphous dissolution mechanisms is an ongoing challenge. Here we outline the novel application using Focused Beam Reflectance Measurement (FBRM) to analyse particle populations orthogonal to USP 2 dissolution. The relative impact of polymer substitution and particle attributes on 25% BMS-708163/HPMC-AS SDD dissolution was assessed. Dissolution mechanisms for SDDs were categorized into erosion versus disintegration. Beyond an initial mixing period, FBRM particle counts diminish slowly and particles are detectable until the point where API dissolution is complete. There is correlation between FBRM particle count decay rate, representing loss of SDD particles in the dissolution media, and UV dissolution rate, measuring dissolved API. For the SDD formulation examined, the degree of succinoyl substitution for HPMC-AS, SDD particle size and surface area all had an impact on dissolution. These data indicate the SDD displayed an erosion mechanism and that FBRM is capturing a rate-limiting step. From this screening tool, the mechanistic understanding and measured impact of polymer chemistry and particle properties can inform a risk-assessment and control strategy for this compound.
关键词： HPMC-AS,FBRM,SDD,substitution,dissolution-mechanism,amorphous,surface area,erosion,dispersion,particle-size
更新于2025-09-23 15:22:29
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Design of a novel dual-axis micro manipulator with an asymmetric compliant structure
摘要： This paper presents a novel piezoelectrically actuated dual-axis micro manipulator with an asymmetric compliant structure. The mechanical design of the micro manipulator is first presented. A novel guiding bridge (GB)-type mechanism was proposed and utilized in the left part of the micro manipulator to improve the dynamic performance of the micro manipulator. The analytical model has been established based on pseudo-rigid-body (PRB) model and matrix-based compliance modeling (MCM) method. The kinematic and the precision of the micro manipulator have been analyzed, and the input and output couplings have been investigated. The prototype of the micro manipulator has been fabricated by wire electro discharge machining (WEDM). Then, open-loop experimental tests have been performed. The experimental results match well with the analytical calculation, and the amplification ratios are 11.12 and 4.64 for left part and right part, respectively. Proportional-integral (PI) controller has been used to regulate the output displacement and grasping force, and a series of closed-loop experiments have been conducted to investigate the performance of the micro manipulator. The results show that the position resolution for both the right and left parts is 0.15 μm, and the force resolution is 4 mN.
关键词： Mechanical design,Piezoelectric actuator,Micro manipulator,Compliant mechanism
更新于2025-09-23 15:22:29