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Effect of Size, Coverage, and Dispersity on the Potential-Controlled Ostwald Ripening of Metal Nanoparticles
摘要： Here we describe the size-dependent, electrochemically-controlled Ostwald ripening of 1.6, 4 and 15 nm diameter Au nanoparticles (NPs) attached to (3-aminopropyl)triethoxysilane (APTES)-modified glass/Indium tin oxide (glass/ITO) electrodes. Holding the Au NP-coated electrodes at a constant potential negative of the dissolution potential in bromide-containing electrolyte led to electrochemical Ostwald ripening of the different-sized Au NPs. The relative increase in the diameter of the NPs (Dfinal/Dinitial) during electrochemical Ostwald ripening increases with decreasing NP size, increasing applied potential, increasing NP population size dispersity, and increasing NP coverage on the electrodes. Monitoring the average size of the Au NPs as a function of time at a controlled potential allows the measurement of the Ostwald ripening rate. Anodic stripping voltammetry (ASV) and electrochemical determination of the surface area-to-volume ratio (SA/V) provides fast and convenient size analysis for the many different samples and conditions, with consistent sizes from scanning electron microscopy (SEM) images for some samples. It is important to better understand electrochemical Ostwald ripening, especially under potential control, since it is a major process that occurs during the synthesis of metal NPs and leads to detrimental size instability during electrochemical applications.
关键词： electrochemical control,surface area-to-volume ratio,anodic stripping voltammetry,size-dependent,metal nanoparticles,Ostwald ripening
更新于2025-09-23 15:19:57
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Layered Nonstoichiometric V <sub/>7</sub> O <sub/>16</sub> Thin Films with Controlled Oxygen-Deficient Multivalent States and Crystalline Phases
摘要： Layered nonstoichiometric vanadium oxides have aroused strong interest in energy conversion, storage, chemical catalysis, sensors and optoelectronic devices. It is still a critical challenge to control unique atomic-layer constructions and oxygen-dependent multivalent states in layered metal oxides. Here, we demonstrated the layered nonstoichiometric V7O16 thin films with controlled multivalent states and crystalline phases obtained by the combination of atomic layer deposition (ALD) and oxygen-dependent crystallization. The nonstoichiometric composition and crystalline microstructures are dominated by the oxidation states of vanadium and the thicknesses of the pristine films during the formation of layered V7O16 thin films. Variable-temperature optical and electrical behaviors suggest that no abrupt electronic and structural transitions are observed in the layered V7O16 thin films at a temperature ranging from 78 to 475 K. We expect that the oxygen-dependent multivalent states and crystalline phases in layered V7O16 will provide more opportunities to fabricate layered oxides and electrochemical devices based on nonstoichiometric vanadium oxides.
关键词： atomic layer deposition,vanadium oxide,layered oxide,V7O16,oxygen-dependent crystallization
更新于2025-09-23 15:19:57
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Frequency-dependent equivalent modelling of broadband air-coupled transducers
摘要： Electrical impedance is an essential parameter for characterizing the performance of transducers during manufacturing and application phases. The Conventional method to model the electrical impedance is based on Butterworth-Van Dyke (BVD) model with constant equivalent parameters, which is valid only in the neighborhood of resonance frequency. In this study, we present a method for modelling the electrical impedance over broadband featuring improved BVD model with frequency-dependent equivalent parameters. In order to obtain frequency-dependent parameters from the measured impedance, estimation is performed in a constrained piecewise and stepwise manner. Firstly, a concise calculation method to obtain initial values of equivalent parameters is presented. Then, the original impedance is equally divided into multiple segments and the resonant segments containing the resonant frequencies are located. New impedance data is reconstructed with one of non-resonant segments and the resonant segments. Finally, with the initial values refined by genetic algorithm (GA), equivalent parameters are obtained from the reconstructed impedance based on GA. The estimation results are assigned to the central frequency point of the non-resonant segment. A new segment is generated by shifting the last non-resonant segment one frequency interval, and data reconstruction and estimation process are repeated till all parameters at each frequency are gained. Frequency-dependent parameters are obtained by the combination of a series of constant parameters at each frequency. The proposed method is verified with good accuracy in modelling of electrical impedance and transmitting response of broadband air-coupled transducer used for gas flow measurement which are difficult to be accurately modelled by the traditional method.
关键词： Electrical impedance,frequency-dependent parameters,improved BVD model,broadband air-coupled transducers
更新于2025-09-23 15:19:57
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Time-energy filtering of single electrons in ballistic waveguides
摘要： Characterizing distinct electron wave packets is a basic task for solid-state electron quantum optics with applications in quantum metrology and sensing. A important circuit element for this task is a non-stationary potential barrier that enables backscattering of chiral particles depending on their energy and time of arrival. Here we solve the quantum mechanical problem of single-particle scattering by a ballistic constriction in an fully depleted quantum Hall system under spatially uniform but time-dependent electrostatic potential modulation. The result describes electrons distributed in time-energy space according to a modi?ed Wigner quasiprobability distribution and scattered with an energy-dependent transmission probability that characterizes constriction in the absence of modulation. Modi?cation of the incoming Wigner distribution due to external time-dependent potential simpli?es in case of linear time-dependence and admits semiclassical interpretation. Our results support a recently proposed and implemented method for measuring time and energy distribution of solitary electrons as a quantum tomography technique, and offer new paths for experimental exploration of on-demand sources of coherent electrons.
关键词： single-electron devices,electron quantum optics,quantum state tomography,time-dependent scattering
更新于2025-09-23 15:19:57
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[IEEE 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - Rome, Italy (2019.6.17-2019.6.20)] 2019 PhotonIcs & Electromagnetics Research Symposium - Spring (PIERS-Spring) - A GaAs Integrated Power Divider Based on Microstrip and LC Structure with Optimized Capacitance
摘要： In this paper, a microstrip LC two-section Wilkinson power divider based on GaAs IPD process is proposed. A method on adjusting circuit parameters is demonstrated, which can compensate the parasitic e?ects of frequency-dependent passive components. One of the sections is a lumped LC network and the other section consists of microstrip lines. This design can reduce the size of the power divider and avoid a high loss. The inductance and capacitance of this power divider are calculated to ensure that the LC network is equivalent to a microstrip line. However, the capacitances and inductances are all sensitive to frequency so there is a signi?cant variation among calculation with ideal components and simulation with practical models. To solve this problem, even-mode input admittance is studied. By plotting a polar diagram of ideal and simulated even-mode input admittances, it is clear that a di?erence exists among simulation and ideal target, which causes the performance degeneration. This polar diagram also indicates a method on optimizing the admittance by increasing capacitance in the LC network. Increased capacitances are utilized in power divider simulation. Simulated results are compared and an optimized capacitance, which guides our ?nal design, is obtained. This power divider is fabricated using GaAs IPD process and measured on wafer. Measurement agrees well with simulation: operation band is 2.850 GHz to 4.832 GHz. A 1.982 GHz bandwidth is achieved. The insertion loss of port 2, 3 is less than 1.30 dB in this frequency range, and the isolation is higher than 18.5 dB.
关键词： frequency-dependent passive components,Wilkinson power divider,GaAs IPD process,microstrip LC,even-mode input admittance
更新于2025-09-23 15:19:57
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Temperature-dependent photoluminescence of cesium lead halide perovskite (CsPbX <sub/>3</sub> , X = Br, Cl, I) quantum dots
摘要： Inorganic halide perovskites (CsPbX3, X = Br, Cl, I) have recently been recognized owing to having good luminescent properties. In this work, the emission peak of these perovskites has been tuned in the region of 451–636 nm by varying the halide ion composition. Temperature-dependent photoluminescence (PL) spectroscopy was used to verify the thermal quenching of PL , blue shifting of band gaps and linewidth of broadening for the CsPbX3 (X = Br, Cl, I) QD films. On the basis of fitting data, the activation energy (ΔE) and Huang–Rhys factor (S) of the CsPbX3 (X = Br, Cl, I) QD films was obtained. On moving from X = I to Br to Cl, the decrease in ΔE indicates that the excited electrons easily returned to the groundstate without the emission of radiation, ΔE decreases as S increases, the increase in the Huang–Rhys factor is indicative of enhanced electron–phonon coupling.
关键词： Huang–Rhys factor,activation energy,CsPbX3,temperature-dependent PL
更新于2025-09-23 15:19:57
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Effect of obliquely external magnetic field on the intense laser pulse propagating in plasma medium
摘要： In this paper, self-focusing of intense laser pulse propagating along the obliquely external magnetic field on the collisional magnetoactive plasma by using the perturbation theory have been studied. The wave equation describing the interaction of intense laser pulse with collisional magnetoactive plasma is derived. In addition, employing source-dependent expansion (SDE) method, the analysis of the laser spot-size is discussed. It is shown that with increasing of the angle in obliquely external magnetic field, the spot-size of laser pulse decreases and as a result laser pulse becomes more focused. Furthermore, it is concluded that the self-focusing quality of the laser pulse has been enhanced due to the presence of obliquely external magnetic field in the collisional magnetoactive plasma. Besides, it is seen that with increasing of ν/?0, the laser spot-size reduces and subsequently the self-focusing of the laser pulse in plasma enhances. Moreover, it is found that changing the collision effect in the magnetoactive plasma leads to increases of self-focusing properties.
关键词： obliquely external magnetic field,Collisional magnetoactive plasma,source-dependent expansion method,laser spot-size,self-focusing
更新于2025-09-23 15:19:57
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Analysis of two-color laser-induced electron emission from a biased metal surface using an exact quantum mechanical solution
摘要： Photoelectron emission from solids, as driven by high-intensity lasers, offers a platform for the coherent control of electron motion on ultrashort spatiotemporal scales. By solving the time-dependent Schr?dinger equation, we present an exact analytical solution for the nonlinear ultrafast electron emission from a dc-biased metal surface illuminated by two-color laser fields. We systematically examine the combined effects of a dc electric field and two-color laser fields. In addition to the remarkable tunability of electron emission processes due to interference from two-color laser fields, we find that a strong dc electric field not only opens up more tunneling emission channels, but also introduces intense modulation to the emission current. We find surprising results that strong current modulation (with respect to the phase difference of the two-color lasers) persists (>70%), even with a large dc bias (i.e., ratio of the electric fields for dc : fundamental laser : second-harmonic laser ～= 1 : 0.5 : 0.07). In the meantime, the average emission current level increases by about three orders of magnitude relative to the case of zero dc bias. Application of our model to time-resolved photoelectron spectroscopy is exemplified and shows that the dynamics of the n-photon excited states depends strongly on the applied dc field. Our study suggests a practical way to maintain a strong modulation to high current photoemission, by the addition of a large dc bias for two-color laser-induced electron emission.
关键词： dc electric field,two-color laser fields,ultrafast electron emission,photoelectron emission,time-dependent Schr?dinger equation
更新于2025-09-23 15:19:57
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[IEEE 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Xiamen, China (2019.12.17-2019.12.20)] 2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall) - Active Modulation of EIT-like Response with a Metal-graphene Hybrid Metasurface in Microwave Regime
摘要： Bipedal locomotion is a popular area of study across multiple fields (e.g., biomechanics, neuroscience, and robotics). Different hypotheses and models have tried explaining how humans achieve stable locomotion. Perturbations that produce shifts in the nominal periodic orbit of the joint kinematics during locomotion could inform about the manner in which the human neuromechanics represent the phase of gait. Ideally, this type of perturbation would modify the progression of the human subject through the gait cycle without deviating from the nominal kinematic orbits of the leg joints. However, there is a lack of publicly available experimental data with this type of perturbation. This paper presents the design and validation of a perturbation mechanism and an experimental protocol capable of producing phase-shifting perturbations of the gait cycle. The effects of this type of perturbation on the gait cycle are statistically quantified and analyzed in order to show that a clean phase shift in the gait cycle was achieved. The data collected during these experiments will be publicly available for the scientific community to test different hypotheses and models of human locomotion.
关键词： phase-dependent behavior,perturbations,Gait analysis,locomotion control
更新于2025-09-23 15:19:57
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Dependence of direct and rescattered photoelectron spectra of fluorine anions on orbital symmetry in a short laser pulse
摘要： We theoretically investigate the photoelectron spectra of ?uorine anions by a few-cycle linearly polarized laser pulse for different atomic orbitals, which are calculated by an exact solution to the time-dependent Schr?dinger equation and by the strong-?eld approximation, respectively. Through the comparison of results by both methods, we show that the initial orbital symmetry strongly affects the main shape of the photoelectron spectra. Based on the saddle-point method, we ?nd that the orbital symmetry only affects the intracycle interference for the low-energy electron spectra. More importantly, it is found that the elastic scattering differential cross section leaves different ?ngerprints in the photoelectron spectra for atomic orbitals with different magnetic quantum numbers.
关键词： ?uorine anions,laser pulse,photoelectron spectra,elastic scattering differential cross section,time-dependent Schr?dinger equation,orbital symmetry,strong-?eld approximation,saddle-point method
更新于2025-09-23 15:19:57