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Interface Stress for Bidirectional Frequency Tuning of Prebuckled Vanadium Dioxide MEMS Resonators
摘要： Interface stress between structural materials and thin film coatings has a significant influence on the resonant frequency of microelectromechanical system (MEMS) resonators. In this work, the axial stress on different types of buckled bridge MEMS resonator structures is controlled through the solid-to-solid phase transition of a VO2 thin film coating. The devices have identical dimensions, but different buckling orientations and profiles due to the combined effect of overetching and residual thermal stress mismatch. Thermal actuation is used to tune the resonant frequency of the device, but the changes in frequency are found to be dependent on the type of buckling for the device. Thermal actuation is achieved by applying an electrical current to integrated heaters, or by uniform substrate heating. Bidirectional tunability is found when substrate heating is used, while Joule heating shows a monotonic change in frequency. This phenomenon can be attributed to the transition in boundary conditions, where the turning points are indicated by the prominent changes in buckling amplitude. In addition, devices with opposite buckling orientations exhibit different tuning behaviors which can be explained by different bending moments induced by beam stress interface modification.
关键词： MEMS resonators,interface stress,buckling,vanadium dioxide,resonant frequency tuning
更新于2025-09-19 17:13:59
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Modification of Graphene Oxide/V <sub/>2</sub> O <sub/>5</sub> ?· <i>n</i> H <sub/>2</sub> O Nanocomposite Films via Direct Laser Irradiation
摘要： Herein, photothermal modification of nanocomposite films consisting of hydrated vanadium pentoxide (V2O5·nH2O) nanoribbons wrapped with graphene oxide (GO) flakes was performed via 405 nm direct laser irradiation. The combination of X-ray diffraction, X-ray photoelectron spectroscopy, Raman scattering, transmission electron microscopy, and scanning electron microscopy allowed comprehensive characterization of physical and chemical changes of GO/V2O5·nH2O nanocomposite films upon photothermal modification. The modified nanocomposite films exhibited porous surface morphology (17.27 m2 g?1) consisting of randomly distributed pillarlike protrusions. The photothermal modification process of GO/V2O5·nH2O enhanced the electrical conductivity of nanocomposite from 1.6 to 6.8 S/m. It was also determined that the direct laser irradiation of GO/V2O5·nH2O resulted in considerable decrease of C?O bounds as well as O?H functional groups with an increase of the laser power density.
关键词： photothermal modification,graphene oxide,functional,nanocomposite,vanadium pentoxide,laser
更新于2025-09-19 17:13:59
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Clinically Colorimetric Diagnostics of Blood Glucose Levels based on Vanadium Oxide Quantum Dots Enzyme Mimics
摘要： The environmental vulnerability of the natural enzyme have always been the most concerned issue in the diagnosis of blood glucose levels, which could be settled by the discovery and application of nanozyme mimics. However, the nanozyme still encountered with the problem of complex preparation process or low enzymatic activities. Herein, peroxidase-like vanadium oxide quantum dots (VOxQDs) were synthesized via a one-step bottom-up solvothermal method using vanadium (Ⅲ) trichloride (VCl3) powder as the precursor. Besides, the most favorable temperature and solvent for VOxQDs synthesis were confirmed. Due to the inherent properties of quantum dots, including larger specific surface areas and more active sites, the as-prepared VOxQDs exhibited 43 times lower value of Km and 32 times higher one of Vmax than those of natural peroxidase using H2O2 as the substrate, indicating the higher affinity and stronger peroxidase-like activity of the VOxQDs nanozymes. Accordingly, a facile and sensitive colorimetric sensor to detect glucose was designed via the integrated enzyme system of VOxQDs and glucose oxidase, which showed wider linear range of 0.005 - 2 mM glucose and lower limit of detection of 1.7 μM compared with those of many other peroxidase-like nanozymes. Especially, the colorimetric sensor was demonstrated with reliable and satisfactory performance in detection of glucose in human serum, which was in good accordance with the clinical results provided from the domestic hospital.
关键词： Peroxidase-like activity,Vanadium oxide quantum dots,Kinetic study,Detection of H2O2 and glucose
更新于2025-09-19 17:13:59
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Solving the Problem of Energy Storage for Solar Photovoltaic Plants (Review)
摘要： Modern storage systems for electric energy generated by solar photovoltaic plants and other renewable energy sources have been analyzed. Among numerous energy storage systems, electrochemical ones, particularly redox battery systems, are of the greatest interest for use in the Central Asia region. The varieties of this energy storage system have been considered, including Zn/Br, Zn/Cl, Fe/Cr, Zn/Se, and Zn/K3Fe(CN)6 systems, as well as promising but underdeveloped iron–iron and lead hybrid operating on electrolytes based on sulfuric acid and with deposition on bipolar electrodes (Pb) and (PbO2), respectively. We have considered the operation principle of vanadium redox batteries, which is based on redox processes that occur in two volumes with vanadium electrolytes separated by a selective membrane. Their advantages for the above goals have been demonstrated. We discuss the prospect of vanadium redox battery production in Uzbekistan based on local vanadium resources in the form of both primary mined materials and manmade raw materials, such as vanadium-containing slags resulting from extraction during metallurgical processing of mined titanium and rare-earth element ores, as well as those formed during the processing of bauxite and phosphorite mined in local deposits. Particular emphasis has been placed on the question of combining the use of domestically produced vanadium pentoxide with developments of electrode surface activation for redox batteries made from graphitized materials with the inclusion of nanoscale particles of metals, such as iron and nickel, using ion-plasma technologies.
关键词： vanadium redox-batteries,electrodes,nanoparticles,vanadium oxide,alternative energy,photovoltaic,vanadium
更新于2025-09-16 10:30:52
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[IEEE 2019 18th International Conference on Optical Communications and Networks (ICOCN) - Huangshan, China (2019.8.5-2019.8.8)] 2019 18th International Conference on Optical Communications and Networks (ICOCN) - The nonlinear optical properties of few-layer VSe <sub/>2</sub> nanosheets
摘要： Vanadium Diselenide (VSe2) has a high electrical conductivity owing to the electron delocalization of the vanadium lattice framework. Most of previous research has been focused on its electronic properties. The nonlinear optical properties of VSe2 have not been investigated yet. Herein, we prepared few-layer VSe2 nanoflakes by liquid phase exfoliation. Subsequently, we utilized Z-scan technique to study the nonlinear optical properties of few-layer VSe2 nanoflakes. And we prepared VSe2 based saturable absorbers (SA) and achieved passively mode-locked operation in Er-doped fiber laser. The results indicate that VSe2 nanosheets own remarkable nonlinear optical properties and could be employed as ideal saturable absorption materials in pulsed fiber lasers.
关键词： Mode-locked,Saturable absorbers,Vanadium Diselenide,Nonlinear optical materials
更新于2025-09-16 10:30:52
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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) - Silicon Photonics at the Interface with a Phase Change Material
摘要： Phase change materials (PCMs) have the ability to control the phase [1], polarization [2], amplitude and coloration [3] of light. Examples of such materials are vanadium dioxide (VO2), GeSbTe and AgInSbTe, which can, owing to changes in their refractive indices, alter the properties of light. Although PCMs have been studied in situations where light propagates from a low-index medium (e.g. air) into the material, there are more possibilities when total internal reflection is involved. In this paper, we investigate the interaction between light travelling in a dense medium with a phase change layer, with particular attention paid to interfaces involving silicon. The possibility of tuning and controlling light at the interface with silicon would be of interest for silicon photonics applications.
关键词： silicon photonics,total internal reflection,vanadium dioxide,Phase change materials,polarization
更新于2025-09-16 10:30:52
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Performance improvement of perovskite solar cells using vanadium oxide interface modification layer
摘要： To improve the performance of perovskite solar cells (PSCs), vanadium oxide (VOx) film was deposited as an interface modification layer (IML) by a radio frequency magnetron sputtering system. The VOx IML was utilized to modify the interface between the indium tin oxide (ITO) anode electrode and the poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT:PSS) hole transport layer (HTL). The valence band maximum (VBM) of 4.94 eV of the VOx films was measured by an ultraviolet photoelectron spectroscopy (UPS). Using the optical energy bandgap and the VBM of the VOx film, the conduction band minimum (CBM) energy level was 2.12 eV. This phenomenon verified that the VOx IML could be an electron blocking layer and made a more match energy level between the work function of ITO anode electrode and the highest occupied molecular orbital (HOMO) of PEDOT:PSS HTL. Using the measurement of contact angle, the surface energy of PEDOT:PSS HTL spun on VOx IML and ITO anode electrode was evaluated as 47.76 mJ/m2 and 38.21 mJ/m2, respectively. The enhanced surface energy of the PEDOT:PSS HTL spun on VOx IML could improve the adhesion ability of the perovskite absorption layer spun on the PEDOT:PSS HTL. Consequently, the carrier extraction could be enhanced and the leakage current could be reduced by the predominant functions of VOx IML. Therefore, the performances of the PSCs were significantly improved. The power conversion efficiency (PCE) of the PSCs with VOx IML was enhanced from 9.43% to 13.69% in comparison with the conventional PSCs without VOx IML.
关键词： Vanadium oxide,Perovskite solar cells,Interface modification layer,Radio frequency magnetron sputtering system
更新于2025-09-16 10:30:52
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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) - Light Manipulation with Plasmonic Structures using Phase Change Materials
摘要： Over the past decade intensive research has focused on the use of plasmonic structures and metamaterials for the control of electromagnetic radiation. Response of such structures is highly dependent on factors set during fabrication, such as the combination of materials used and as well as their structural dimensions. Despite having many promising optoelectronic applications, the inability to tune the optical response of such structures post fabrication presents serious limitations. To overcome this, we present tunable plasmonic elements formed of plasmonic nanostructures on a thin film of vanadium dioxide (VO2), a phase change material. VO2 is an attractive option as a phase change material due to its large, reversible transition from a semiconducting to a metallic phase at a critical temperature of 68°C, close to room temperature. While much research on VO2 is centred on the large changes in the optical properties occurring in the NIR spectral range (above 1μm) upon the phase transition, in this work we focus on the changes in the dielectric function of VO2 in the visible spectral range. In particular, we experimentally and numerically investigate the possibility to use the phase change of VO2 to dynamically tune the plasmonic properties of noble metal nanostructures as well as to manipulate the emission properties of quantum emitters near plasmonic nanostructures. We observe a drastic change in the plasmonic properties of gold nanorods arrays fabricated on a thin layer of VO2 as the phase transition from the semiconducting to metallic phase of VO2 is thermally triggered. Upon phase transition, a >50% decrease in scattering in the red spectral region, especially around 650 nm, was detected in dark field scattering experiments (Figure 1a). Moreover, our spectrally and time resolved measurements reveal that the emission properties of quantum dots (CdSeS/ZnS) in the vicinity of the gold nanorod arrays can be modified through the thermal phase change of the underlying thin layer of VO2 (Figure 1b). When VO2 is in its semiconducting phase the photoluminescence (PL) of QDs on the nanorods array is quenched compared to the PL of QDs on the same VO2 thin film but off the array. In contrast, we observe an enhanced light emission of QDs on the array when the VO2 layer is in its thermally actuated metallic phase. Additionally, the main PL emission peaks of QDs on the nanorod arrays as well as off the arrays red shift by 15 nm, as an effect of heating. The experimental results are accompanied by supporting FDTD simulations.
关键词： photoluminescence,vanadium dioxide,plasmonic structures,quantum dots,phase change materials
更新于2025-09-16 10:30:52
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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) - Low-Voltage Tuning of the Terahertz Passband Transmission using a Tungsten-Doped VO <sub/>2</sub> -Based Metamaterial
摘要： Vanadium dioxide (VO2), which exhibits a semiconductor-metal phase transition at temperatures close to room temperature of 340 K, has been used as a suitable material for carrying out metamaterials that are artificially designed assemblies consisting of subwavelength lattice arrays with unnatural electromagnetic properties in applications such as filters, modulators, and absorbers in the terahertz (THz) frequency range [1-3]. We have demonstrated that the square-loop metamaterial (SLM) can precisely control the amplitude in the range of 0.3–0.6 THz at low voltages below 2 V, when the SLM is combined with tungsten (W)-doped VO2 film. Unlike an undoped-VO2-film-based device with a digital-type switching amplitude response, the device with a 1.2 at.% W-doped VO2 film performed a modulation depth (MD) of 0.72 @0.4 THz, where MD = ((E^2@0V - E^2@2V)/E^2@0V), for transmission of the THz wave in a polarization state perpendicular to the voltage bias line (the direction of the transmitted linear-polarized THz electric-field perpendicular to the voltage bias line pattern of the SLM structure). The proposed metamaterials in the form of the double-square structure connected together can define the desired passband by the resonances derived from each square-loop. In addition, the transmittance of the THz wave was continuously tuned by using the W-doped VO2 thin film formed by the sol-gel method as a substrate. These phase-change material-coupled metamaterial structures can be utilized in analog/digital modulators and bandpass filter applications in the THz frequency region.
关键词： tungsten-doped,low-voltage tuning,metamaterial,terahertz,Vanadium dioxide
更新于2025-09-11 14:15:04
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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