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- 2019
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- Organic light-emitting diodes
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- Electrohydrodynamic printing
- Optoelectronic Information Materials and Devices
- South China University of Technology
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The effect of pulse duration on nanoparticle generation in pulsed laser ablation in liquids: Insights from large-scale atomistic simulations
摘要： The generation of colloidal solutions of chemically clean nanoparticles through pulsed laser ablation in liquids (PLAL) has evolved into a thriving research field that impacts industrial applications. The complexity and multiscale nature of PLAL make it difficult to untangle the various processes involved in the generation of nanoparticles and establish the dependence of nanoparticle yield and size distribution on the irradiation parameters. Large-scale atomistic simulations have yielded important insights into the fundamental mechanisms of ultrashort (femtoseconds to tens of picoseconds) PLAL and provided a plausible explanation of the origin of the experimentally observed bimodal nanoparticle size distributions. In this paper, we extend the atomistic simulations to short (hundreds of picoseconds to nanoseconds) laser pulses and focus our attention on the effect of the pulse duration on the mechanisms responsible for the generation of nanoparticles at the initial dynamic stage of laser ablation. Three distinct nanoparticle generation mechanisms operating at different stages of the ablation process and in different parts of the emerging cavitation bubble are identified in the simulations. These mechanisms are (1) the formation of a thin transient metal layer at the interface between the ablation plume and water environment followed by its decomposition into large molten nanoparticles, (2) nucleation, growth, and rapid cooling/solidification of small nanoparticles at the very front of the emerging cavitation bubble, above the transient interfacial metal layer, and (3) spinodal decomposition of a part of the ablation plume located below the transient interfacial layer, leading to the formation of a large population of nanoparticles growing in a high-temperature environment through inter-particle collisions and coalescence. The coexistence of the three distinct mechanisms of the nanoparticle formation at the initial stage of the ablation process can be related to the broad nanoparticle size distributions commonly observed in nanosecond PLAL experiments. The strong dependence of the nanoparticle cooling and solidification rates on the location within the low-density metal-water mixing region has important implications for the long-term evolution of the nanoparticle size distribution, as well as for the ability to quench the nanoparticle growth or dope them by adding surface-active agents or doping elements to the liquid environment.
关键词： phase explosion,pulsed laser ablation in liquids,molecular dynamics simulations,hydrodynamic instability,atomistic simulations,nanoparticles,nucleation and growth
更新于2025-09-19 17:13:59
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Impact of Surface Roughness in Nanogap Plasmonic Systems
摘要： Recent results have shown unprecedented control over separation distances between two metallic elements hundreds of nanometers in size, underlying the effects of free-electron nonlocal response also at mid-infrared wavelengths. Most of metallic systems however, still suffer from some degree of inhomogeneity due to fabrication-induced surface roughness. Nanoscale roughness in such systems might hinder the understanding of the role of microscopic interactions. Here we investigate the effect of surface roughness in coaxial nanoapertures resonating at mid-infrared frequencies. We show that although random roughness shifts the resonances in an unpredictable way, the impact of nonlocal effects can still be clearly observed. Roughness-induced perturbation on the peak resonance of the system shows a strong correlation with the effective gap size of the individual samples. Fluctuations due to fabrication imperfections then can be suppressed by performing measurements on structure ensembles in which averaging over a large number of samples provides a precise measure of the ideal system’s optical properties.
关键词： hydrodynamic model,nonlocal response,coaxial aperture,plasmonics,epsilon-near-zero mode,surface roughness
更新于2025-09-19 17:13:59
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Plasmon enhanced second harmonic generation by periodic arrays of triangular nanoholes coupled to quantum emitters
摘要： Optical properties of periodic arrays of nanoholes of a triangular shape with experimentally realizable parameters are examined in both linear and nonlinear regimes. By utilizing a fully vectorial three-dimensional approach based on the nonlinear hydrodynamic Drude model describing metal coupled to Maxwell’s equations and Bloch equations for molecular emitters, we analyze linear transmission, reflection, and nonlinear power spectra. Rigorous numerical calculations demonstrating second and third harmonic generation by the triangular hole arrays are performed. It is shown that both the Coulomb interaction of conduction electrons and the convective term contribute on equal footing to the nonlinear response of metal. It is demonstrated that the energy conversion efficiency in the second harmonic process is the highest when the system is pumped at the localized surface plasmon resonance. When molecular emitters are placed on a surface of the hole array line shapes, the second harmonic signal exhibits three peaks corresponding to second harmonics of the localized surface plasmon mode and upper and lower polaritonic states.
关键词： strong coupling,second harmonic generation,hydrodynamic Drude model,plasmonics,nonlinear optics
更新于2025-09-19 17:13:59
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Hydrodynamic simulation of InGaAs terahertz oscillations
摘要： Terahertz (THz) oscillations in n+nn+ In0.53Ga0.47As diodes have been simulated with the use of a time-dependent hydrodynamic model. Under proper biased voltage and doping concentration, THz self-oscillations show up. The current self-oscillations originate from the formation and propagation of electric field domains in In0.53Ga0.47As diodes. The In0.53Ga0.47As device studied here may be presented as an excellent candidate as a solid-state THz source for monolithic integration.
关键词： Terahertz oscillations,hydrodynamic model,InGaAs
更新于2025-09-19 17:13:59
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A Review on the Application of Integral Equation‐Based Computational Methods to Scattering Problems in Plasmonics
摘要： Many computational methods have been developed and used for modeling, understanding, and tailoring extreme optical effects at the nanoscale. Among them, this review focuses on the integral equation-based methods: within the local response limit, a potential-based boundary integral equation (BIE) formalism and a field-based volume integral equation (VIE) formalism; within the nonlocal hydrodynamic model, a potential-based BIE formalism. These formalisms are derived from macroscopic electrodynamics (together with appropriate constitutive relations). The derivations are based on three pillars: the Green function, the field relation(s) (for the VIE formalism, the incident—scattered—total field relation; for the BIE formalism, the interface conditions connecting the fields at two sides of the interface), and the field equivalence principle (for the VIE formalism, the volume equivalence principle; for the BIE formalism, the Huygens principle). By applying the method of moments (MoM) algorithm, the derived integral equations are converted into matrix equations, with possible problems in the implementation being discussed. Levels of solutions, including the eigenmode and natural mode solutions, and group representation theory are introduced as powerful post-processing steps. Many examples are shown to demonstrate the effectiveness of the reviewed algorithms.
关键词： nonlocal hydrodynamic model,computational electromagnetics,boundary integral equations,plasmonics,volume integral equations
更新于2025-09-19 17:13:59
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Electro-Hydrodynamic Design of an Intelligent Balloon Water Gate Controlled by an Efficient Maximum-Power-Seeking Controller for a Solar Generation System
摘要： The intelligent balloon water gate (IBWG) invention is a hydraulic gate model made of reinforced plastic that controls the water level (WL) downstream or upstream of a barrage. The IBWG automatically in?ates and de?ates by compressed air to close and open the water passage, respectively. The whole design consists of a balloon, a waterway, sensors, an air compressor, a control panel, an electrical circuit and a photovoltaic generation (PVG) system. The Tyass barrage in Iraq was considered as a case study. The Tyass barrage was built with concrete and four sliding steel water gates and redesigned using the IBWG. The originality of the current research resides in the combination of the IBWG mechanism with an ef?cient maximum power point (MPP) seeking controller for a photovoltaic generation system, which is one of the most promising sources of renewable energy in the world. To the best of our knowledge, in this ?eld, this scenario has not yet been discussed in detail. Upper and lower water sensors are used to control the IBWG. The upper sensor sends a signal to the control panel when the downstream water level reaches its maximum value to open the air inlet valve and close the outlet valve, in?ating 14 IBWGs with a volume of 3.5 m3 under 122 psi of pressure and closing the water passage. When the WL decreases below the minimum level, the lower sensor initiates the opposite procedure. The air compressor automatically ?lls the air tank to 181 psi and is supplied by a 24 VDC AGM rechargeable battery with a capacity of 40-60 Ah, which is charged by four solar panels connected in parallel and exposed to an average of 8.8 hrs/day of sunshine. The proposed MPP-seeking controller was implemented by a backstepping design coupled with the grey wolf mechanism. The solar irradiance data were observed 39 years ago. The proposed controller is capable of following the MPP with minimum oscillations under an external irradiance variation. The IBWG system is veri?ed at night or during the early morning when the sun is not active. Nevertheless, it is possible to store compressed air in an auxiliary tank to avoid emergencies such as partial shading conditions.
关键词： PVG system,backstepping technique,lyapunov stability,grey wolf optimization,Electro-hydrodynamic rubber water gate
更新于2025-09-16 10:30:52
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A quantitative analysis of memory effects in the viscously coupled dynamics of optically trapped Brownian particles
摘要： We provide a quantitative description of the memory e?ects existing in the apparently random Markovian dynamics of a pair of optically trapped colloidal microparticles in water. The particles are trapped in very close proximity to each other such that the resultant hydrodynamic interactions lead to non-Markovian signatures manifested by the double exponential auto-correlation function for the Brownian motion of each particle. In connection with the memory e?ects, we quantify the storage of energy in terms of various system parameters and demonstrate that a pair of Markovian particles – confined in individual optical traps in a viscous fluid – can be described in the framework of a single Brownian particle in a viscoelastic medium. We define and quantify the equivalent storage and loss moduli of the two-particle system, and show experimentally that the memory effects are maximized at a certain trap stiffness ratio, and reduce with increasing particle separation. The technique can be generally used to determine the effective viscoelastic parameters of any such fluid–particle systems, and can thus help understand the interactions between active particles mediated by simple or complex fluids.
关键词： memory effects,non-Markovian signatures,hydrodynamic interactions,viscoelastic medium,optically trapped colloidal microparticles
更新于2025-09-16 10:30:52
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Electronic–Electromagnetic Multiphysics Modeling for Terahertz Plasmonics: A Review
摘要： In this article, we review numerical and analytical methods of electronic–electromagnetic multiphysics modeling for terahertz plasmonic applications. Approaches within semiclassical regime of electronic transport are considered, as these are appropriate for examining plasma-wave phenomenology in 2-D electron gas systems, commonly found in high-electron-mobility transistors (HEMTs) and graphene sheets. In modeling of such electronic–plasmonic devices, coupling of incident electromagnetic wave to the device or emission from the device needs to be modeled. Therefore, electronic–electromagnetic coupled multiphysics multiscale models are required. In such modeling problems, the domain consists of large regions where electrodynamic equations are to be solved. Therefore, overall time efficiency relies on the speed of solution of electrodynamic equations. Nevertheless, the electrodynamic solution’s speed is limited by the smallest grid sizes, which are a function of electronic transport equations. To address these issues, unconditionally stable finite-difference time-domain (FDTD) and iterative alternating directional implicit (ADI)-FDTD methods, coupled with hydrodynamic equations, are reviewed. Advantages and compromises between FDTD, ADI-FDTD, and iterative ADI-FDTD-based global modeling are discussed and conclusions are summarized.
关键词： electronic,numerical modeling,electron transport,terahertz (THz),FDTD,multiphysics,plasmonic,Alternating directional implicit finite-difference time-domain (ADI-FDTD),multiscale modeling,hydrodynamic (HD),plasma wave,electromagnetic
更新于2025-09-16 10:30:52
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Modal analysis for nanoplasmonics with nonlocal material properties
摘要： Plasmonic devices with feature sizes of a few nanometers exhibit effects which can be described by the nonlocal hydrodynamic Drude model. We demonstrate how to exploit contour integral methods for computing eigenfrequencies and resonant states of such systems. We propose an approach for deriving the modal expansion of relevant physical observables. We use the methods to perform a modal analysis for a metal nanowire. All complex eigenfrequencies in a large frequency range and the corresponding resonant states are computed. We identify those resonant states which are relevant for the extinction cross section of the nanowire.
关键词： extinction cross section,nanoplasmonics,hydrodynamic Drude model,modal analysis,nonlocal material properties,metal nanowire
更新于2025-09-16 10:30:52
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Temperature Variations of Gold Nanoparticle and Dynamics of Plasmonic Bubble in Water Under Nanosecond Pulsed Laser
摘要： Suspended gold nanoparticle in water medium starts to warm up under nanosecond laser irradiation and creates a bubble around itself. The present study aims at evaluating the amount of nanoparticle size reduction at boiling temperature, the temperature variations of the nanoparticle, and its medium and finally the bubble formation moment. To this aim, Mie theory was used to calculate the absorption cross section of the nanoparticle in proximity of the bubble. Heat transfer equations were applied to determine the temperature of the nanoparticle and water. In addition, hydrodynamic equations were initiated to evaluate the expansion of the bubble. Then, these three groups of equations were coupled together and solved numerically. Based on the results, the bubble forms at the critical pressure and consequently due to the slow bubble velocity, temperature gradient in the medium is observed. Further, slight pulse width variations play a significant role on the nanoparticle temperature. The calculation of the nanoparticle heating associated with the creation of the bubble helps in controlling nanoparticle size and understanding the nanoscale heat transfer processes.
关键词： Gold nanoparticle,Nano bubble,Nanoparticle heating,Hydrodynamic equations
更新于2025-09-12 10:27:22