Local Field Distribution Research Articles

Selective controlling transverse plasmon spectrum of pentagonal gold nanotube: from visible to near-infrared region

In this paper, the optical properties and local electric field distribution of transverse plasmon mode of a single pentagonal gold nanotube are studied for the first time by the discrete dipole approximation (DDA). We find that the transverse plasmon peaks can nonlinearly red shift from visible to infrared region via controlling the inner diameter. In addition, the transverse plasmon peak firstly blue shifts and then red shifts in the visible region with the increase of outer diameter. Further analysis shows that the spectra red shift with the increase of outer diameters when scattering is dominant. Local electric field analysis reveals that transverse plasmon resonance peaks of gold nanotube mainly come from dipole resonance. When the tube wall is thin enough, multi-polar plasmon resonance mode will be generated, and the number of peaks will be increased. The surface charges of inner and outer tube walls are changed by tuning the inner diameter and outer diameter parameters of pentagonal gold nanotube. The selective controlling transverse plasmon spectra of gold nanotube are realized, which is of great significance to the study of optical properties of gold nanotube and the application of molecular detection and biological imaging.

Muon-Spin Motion at the Crossover Regime between Gaussian and Lorentzian Distribution of Magnetic Fields

Abstract The muon spin relaxation method (μSR) is a powerful microscopic tool to probe electronic states of materials observing local magnetic field distributions on the muon. It often happens that a distribution of local magnetic fields shows intermediate state between Gaussian and Lorentzian shapes. In order to generally describe intermediate field distributions, we dealt the convolution of two isotropic distributions in the three dimension and derived exact muon-spin relaxation functions which can be applied to all crossover regimes between the Gaussian and Lorentzian.

Plasmonic metamaterial absorbers with strong coupling effects for small pixel infrared detectors

Here we report a metal-insulator-metal (MIM) based infrared plasmonic metamaterial absorber consisting of deep subwavelength meander line nanoantennas. High absorption composed of two-hybrid modes from 11 μm to 14 μm is experimentally demonstrated with a pixel pitch of 1.47 μm corresponding to a compression ratio of 8.57. The physical mechanisms responsible for novelty spectral absorption, including the strong coupling between the plasmon resonances and the phonon vibrations, material loss from the dielectric spacer, localized surface plasmon resonance (LSPR), and Berreman mode excited by oblique incidence, have been systematically analyzed by finite-difference time-domain (FDTD) method, Fabry-Perot resonance model and two-coupled damped oscillator model. At oblique incidence, a spectral splitting related to the strong coupling between LSPR mode and Berreman mode is also observed. The distribution of local electromagnetic fields and ohmic loss are numerically investigated. Moreover, we evaluate the absorption performances with finite-sized arrays. We also show that the absorber can maintain its absorption with a 2 × 2 nanoantenna array. Such a miniaturized absorber can adapt to infrared focal plane arrays with a pixel size smaller than 5 μm, and thermal analysis is also performed. Our approach provides an effective way to minimize the antenna footprint without undermining the absorber performances, paving the way towards its integration with small pixels of infrared focal plane arrays for enhanced performances and expanded functionalities.

Van der Waals Phonon Polariton Microstructures: Van der Waals Phonon Polariton Microstructures for Configurable Infrared Electromagnetic Field Localizations (Adv. Sci. 13/2021)

In article number 2004872, Huanjun Chen, Shaozhi Deng, and co-workers realize a nanoscale tailoring of mid-infrared electromagnetic field localizations in van der Waals α-MoO3 microstructures of different shapes and sizes. This is enabled by the synergy of in-plane hyperbolic phonon polaritons and spatial confinement effects. Furthermore, the authors show that orientation of the in-plane isofrequency curve relative to the microstructure edge is a critical parameter governing the localized electromagnetic field distributions.

Structural analysis of FRP laminate with triangle convexities (FLTC) using the VAM-based equivalent model

To comprehensively study the static and dynamic behaviors of fiber-reinforced polymer (FRP) laminates with triangle convexities (FLTC) under different boundary conditions and avoid structural damage, an equivalent model of the FLTC was developed based on the variational asymptotic method. A constitutive model of the unit cell was developed to obtain the constitutive relations that could be used as effective plate properties of the two-dimensional equivalent plate model (2D-EPM). The accuracy of the equivalent model and the obtained equivalent stiffness were verified by comparing with the global displacement, buckling modes, critical loads, free-vibration modes, and frequencies of a three-dimensional finite element model (3D-FEM). The influence of different layup configurations, structural arrangements and geometric parameters on the effective performance of the FLTC are discussed. The results showed that the critical load and natural frequencies obtained using the equivalent model were in good agreement with those obtained from the 3D-FEM, and the local field distributions within the unit cell of the FLTC were well captured. The free vibration and global buckling of the FLTC were closely related to the geometric sizes and layup configurations. Most importantly, the calculation efficiency was greatly improved. The research results provide a reference for the practical application of the FLTC in civil engineering.

Optical absorption tunability and local electric field distribution of gold-dielectric-silver three-layered cylindrical nanotube* *Project supportedby the Programs for Anhui Provincial Natural Science Foundation, China (Grant Nos. 1808085MA20 and 1808085MA05), Excellent Young Talents in University of Anhui Province, China (Grant No. gxyq2017027), the Key Scientific Research Foundation of Anhui Provincial Education Department, China (Grant Nos. KJ2019A0564 and KJ2018A0366), the Key Research

The effects of inner nanowire radius, shell thickness, the dielectric functions of middle layer and surrounding medium on localized surface plasmon resonance (LSPR) of gold-dielectric-silver nanotube are studied based on the quasi-staticapproximation. Theoretical calculation results show that LSPR of gold-dielectric-silver nanotube and LSPR numbers can bewell optimized by adjusting its geometrical parameters. The longer wavelength of mode takes place a distinct red-shift with increasing the inner nanowire radius and the thickness of middle dielectric layer,while a blue-shift with increasing outer nanotube thickness. The physical mechanisms are explained based on the plasmon hybridization theory, induced charges and phase retardation. In addition, the effects of middle dielectric function and surrounding medium on LSPR, and the local electric field factor are also reported. Our study provides the potential appications of gold-dielectric-silver nanotube in biological tissues, sensor and related regions.

Static and dynamic analysis of hemispherical convex-concave composite plate (HCCP) using variational asymptotic equivalent model

In order to deeply study the static and dynamic behavior of hemispherical convex-concave composite plate (HCCP) under different conditions and avoid structural damage, the equivalent model of HCCP was developed based on variational asymptotic method. The constitutive modeling of unit cell was carried out to obtain the constitutive relations that can be used as effective plate properties for the 2-D equivalent plate model (2D-EPM). The accuracy of the equivalent model and the obtained equivalent stiffness are verified by comparing with the static displacement, global buckling and free-vibration of 3D finite element model (3D-FEM). The influence of different layup configurations of laminates and geometric parameters on the equivalent stiffness, vibration characteristics and global buckling of HCCP are discussed. The results show that the buckling loads and natural frequencies obtained by using equivalent model are in good agreement with 3D-FEM. The vibration and buckling of HCCP are closely related to the geometric sizes and layup configurations of the laminate, and the local field distributions within the unit cell of HCCP are well captured. Most importantly, the calculation efficiency is greatly improved. The research results provide a reference for the practical application of HCCP in the civil engineering.

Geometrical frustration and cluster spin glass with random graphs

We develop a based on a sparse random graph to account for the interplay between geometric frustration and disorder in cluster magnetism. Our theory allows introduction of the cluster network connectivity as a controllable parameter. Two types of inner cluster geometry are considered: triangular and tetrahedral. The theory was developed for general, nonuniform intracluster interactions, but in the present paper the results presented correspond to uniform, antiferromagnetic (AF) intraclusters interaction J_{0}/J. The clusters are represented by nodes on a finite connectivity random graph, and the intercluster interactions are randomly Gaussian distributed. The graph realizations are treated in replica theory using the formalism of order parameter functions, which allows one to calculate the distribution of local fields and, as a consequence, the relevant observable. In the case of triangular cluster geometry, there is the onset of a classical spin liquid state at a temperature T^{*}/J and then, a cluster spin glass (CSG) phase at a temperature T_{/}J. The CSG ground state is robust even for very weak disorder or large negative J_{0}/J. These results does not depend on the network connectivity. Nevertheless, variations in the connectivity strongly affect the level of frustration f_{p}=-Θ_{CW}/T_{f} for large J_{0}/J. In contrast, for the nonfrustrated tetrahedral cluster geometry, the CSG ground state is suppressed for weak disorder or large negative J_{0}/J. The CSG boundary phase presents a reentrance which is dependent on the network connectivity.

Van der Waals Phonon Polariton Microstructures for Configurable Infrared Electromagnetic Field Localizations

AbstractPolar van der Waals (vdW) crystals that support phonon polaritons have recently attracted much attention because they can confine infrared and terahertz (THz) light to deeply subwavelength dimensions, allowing for the guiding and manipulation of light at the nanoscale. The practical applications of these crystals in devices rely strongly on deterministic engineering of their spatially localized electromagnetic field distributions, which has remained challenging. The polariton interference can be enhanced and tailored by patterning the vdW crystal α‐MoO3 into microstructures that support highly in‐plane anisotropic phonon polaritons. The orientation of the polaritonic in‐plane isofrequency curve relative to the microstructure edges is a critical parameter governing the polariton interference, rendering the configuration of infrared electromagnetic field localizations by enabling the tuning of the microstructure size and shape and the excitation frequency. Thus, the study presents an effective rationale for engineering infrared light flow in planar photonic devices.

Near-Field Excited Archimedean-like Tiling Patterns in Phonon-Polaritonic Crystals

Phonon-polaritons (PhPs) arise from the strong coupling of photons to optical phonons. They offer light confinement and harnessing below the diffraction limit for applications including sensing, imaging, superlensing, and photonics-based communications. However, structures consisting of both suspended and supported hyperbolic materials on periodic dielectric substrates are yet to be explored. Here we investigate phonon-polaritonic crystals (PPCs) that incorporate hyperbolic hexagonal boron nitride (hBN) to a silicon-based photonic crystal. By using the near-field excitation in scattering-type scanning near-field optical microscopy (s-SNOM), we resolved two types of repetitive local field distribution patterns resembling the Archimedean-like tiling on hBN-based PPCs, i.e., dipolar-like field distributions and highly dispersive PhP interference patterns. We demonstrate the tunability of PPC band structures by varying the thickness of hyperbolic materials, supported by numerical simulations. Lastly, we conducted scattering-type nanoIR spectroscopy to confirm the interaction of hBN with photonic crystals. The introduced PPCs will provide the base for fabricating essential subdiffraction components of advanced optical systems in the mid-IR range.

Patterning of transition metal dichalcogenides catalyzed by surface plasmons with atomic precision

Summary Plasmon-induced charge transfer has drawn considerable interests and spurred rapid developments of photovoltaics and photocatalysis. Various plasmonic metal/transition metal dichalcogenide (TMD) heterostructures have been developed to promote charge separation. For plasmon-induced catalysis, the transformation of TMDs is rare, and the erosion of TMDs has not yet been reported. Here, we report the etching of two-dimensional TMDs by planar surface plasmon polaritons (SPPs). We found that SPPs can etch various TMDs into desired layers and lateral size through controlling the light power and incident direction. In aqueous media, the strong plasmonic coupling at Au/MoS2 interface generates holes in the valence band of MoS2 that can weaken its interlayer interaction. As a synergistic effect, the plasmonic hot electrons produce oxidizing H2O2 to dissolve MoS2 from the top layers. Our results provide a new perspective for understanding the plasmonic coupling at metal-TMD interfaces and a reliable route toward fabricating well-defined TMDs.

Suspended MoS2 Photodetector Using Patterned Sapphire Substrate

AbstractThe introduction of patterned sapphire substrates (PSS) has been regarded as an effective method to improve the photoelectric performance of 2D layered materials in recent years. Molybdenum disulfide (MoS2), an intriguing transition metal 2D materials with splendid photoresponse owing to a direct‐indirect bandgap transition at monolayer, shows promising optoelectronics applications. Here, a large‐scale, continuous multilayer MoS2 film is prepared on a SiO2/Si substrate and transferred to flat sapphire substrate and PSS, respectively. An enhanced dynamic distribution of local electric field and concentrated photon excitons across the interface between MoS2 and patterned sapphire substrates are revealed by the finite‐difference time‐domain simulation. The photoelectric performance of the MoS2/PSS photodetector is improved under the three lasers of 365, 460, and 660 nm. Under the 365 nm laser, the photocurrent increased by 3 times, noise equivalent power (NEP) decreases to 1.77 × 10−14 W/Hz1/2 and specific detectivity (D*) increases to 1.2 × 1010 Jones. Meanwhile, the responsivity is increased by 7 times at 460 nm, and the response time of the MoS2/PSS photodetector is also shortened under three wavelengths. The work demonstrates an effective method for enhancing the optical properties of photodetectors and enabling simultaneous detection of broad‐spectrum emissions.

High efficiency analysis model for composite honeycomb sandwich plate by using variational asymptotic method

In this article, an equivalent model (called the two-dimensional equivalent plate model (2D-EPM)) of a composite honeycomb sandwich plate (CHSP) is developed using the variational asymptotic method (VAM). The three-dimensional (3D) geometric nonlinear problem of the CHSP is decoupled into a linear constitutive model over a unit cell and a geometric nonlinear problem defined in the 2D-EPM. In the linear constitutive model, the equivalent plate properties are calculated and imported into the 2D-EPM to carry out static, buckling, and vibration analysis. The effects of the layup configurations of the face sheet, geometric parameters of the honeycomb core, and boundary conditions on the equivalent stiffness and the static, buckling, and free-vibration responses are systematically studied. Compared with the 3D finite element method and 3D traditional equivalent model, the 2D-EPM possesses the merits of high precision and calculation efficiency. The equivalent stiffness and anisotropy of the CHSP are very sensitive to the layup configuration as well as the side length and cell corrugation angle of the honeycomb core. The present model can accurately capture the local field distribution within the unit cell as well as provides an effective method for the design and optimization of the CHSP.

Evaluation of piezoelectric and mechanical properties of the piezoelectric composites with local damages

Microscopic voids/defects always occur in brittle piezoelectric fiber during the preparation. In addition, inconsistent material properties between the reinforced fibers and the matrix led to some microcracks located at the interface in matrix materials. In order to obtain equivalent properties of piezoelectric composites with respect to initial voids/defects, a parametric microscopic finite-volume model was constructed in this paper. To this end, the mechanical-electric coupling constitutive relation was implanted into the parametric FVDAM model to describe their piezoelectric characteristics. To verify the presented coupled mechanical-electric model, the numerical results of local stress and electric field distributions acquired by finite element method were also indicated for a comparison. On this basis, equivalent modulus and equivalent electrical properties with full consideration of local damages were also investigated by the presented microscale model.

Proximity-induced electrodeformation and membrane capacitance coupling between cells

Membrane capacitance and transmembrane potential are sensitive to the proximity of neighboring biological cells which eventually induces anisotropic perturbation of the local electric field distribution in a cell assembly and/or a tissue. The development of robust and reliable multiphysics approaches is essential to solve the challenge of analyzing proximity-induced capacitance coupling (CC) between cells. In this study, we ask to what extent this CC is a minor perturbation on the individual cells or whether it can fundamentally affect bio-electromechanical cues. A key component of our continuum electromechanical analysis is the consideration of elastic models of cells under steady state electric field excitation to characterize electrodeformation (ED). Analyzing the difference between the ED force for a pair of cells and its counterpart for a single reference cell allows us to determine a separation distance-orientation angle diagram providing evidence of a separation distance beyond which the electrostatic interactions between a pair of biological cells become inconsequential for the ED. An attenuation-amplification transition of ED force in this diagram suggests that anisotropy induced by the orientation angle of the cell pair relative to the applied electric field direction has a significant influence on ED and CC. We furthermore observe that the shape of this diagram changes when extracellular conductivity is varied. The results obtained are then contrasted with the corresponding diagrams of similar cell configurations under an oscillating electric field excitation below and above the α-dispersion frequency. This investigation may provide new opportunities for further assessment of electromechanical properties of engineered tissues.

Understanding the Role of Different Substrate Geometries for Achieving Optimum Tip-Enhanced Raman Scattering Sensitivity.

Tip-enhanced Raman spectroscopy (TERS) has experienced tremendous progress over the last two decades. Despite detecting single molecules and achieving sub-nanometer spatial resolution, attaining high TERS sensitivity is still a challenging task due to low reproducibility of tip fabrication, especially regarding very sharp tip apices. Here, we present an approach for achieving strong TERS sensitivity via a systematic study of the near-field enhancement properties in the so-called gap-mode TERS configurations using the combination of finite element method (FEM) simulations and TERS experiments. In the simulation study, a gold tip apex is fixed at 80 nm of diameter, and the substrate consists of 20 nm high gold nanodiscs with diameter varying from 5 nm to 120 nm placed on a flat extended gold substrate. The local electric field distributions are computed in the spectral range from 500 nm to 800 nm with the tip placed both at the center and the edge of the gold nanostructure. The model is then compared with the typical gap-mode TERS configuration, in which a tip of varying diameter from 2 nm to 160 nm is placed in the proximity of a gold thin film. Our simulations show that the tip-nanodisc combined system provides much improved TERS sensitivity compared to the conventional gap-mode TERS configuration. We find that for the same tip diameter, the spatial resolution achieved in the tip-nanodisc model is much better than that observed in the conventional gap-mode TERS, which requires a very sharp metal tip to achieve the same spatial resolution on an extended metal substrate. Finally, TERS experiments are conducted on gold nanodisc arrays using home-built gold tips to validate our simulation results. Our simulations provide a guide for designing and realization of both high-spatial resolution and strong TERS intensity in future TERS experiments.

Double enhanced energy storage density via polarization gradient design in ferroelectric poly(vinylidene fluoride)-based nanocomposites

Encapsulating ferroelectric ceramic nanofillers into polymer matrix with various architectures has been demonstrated as an effective strategy for ultrahigh energy storage density. Nevertheless, large discrepancy in permittivities between ceramic fillers and polymer requires sophisticated interfacial modification to alleviate local charge concentration. The idea to design graded permittivity from the filler center to surrounding matrix in composites is promising, yet remains a big challenge. Here coaxial electrospinning technique has been employed to control the polarization gradient distribution in TiO2 nanofibers (TOnf) and poly(vinylidene fluoride)/poly(vinylidene fluoride-co-trifluoroethylene) [PVDF/P(VDF-TrFE)] core-shell structured hybrid nanocomposites system where TOnf is fixed at volume fraction 2%, and the polarization gradient of the polymer is adjusted via altering the volume ratios of PVDF and P(VDF-TrFE) in the coaxial electrospun polymer blends in two layers, respectively. Compared with nanocomposites made from mixed solution electrospun randomly and oriented TOnf-PVDF/P(VDF-TrFE) at the same constituent volume fraction, the dielectric losses of coaxial-spun films decrease more than twice, from 0.087 for random nanocomposite film to 0.028, and more intriguingly, the discharged energy storage density (Ue) doubled increasing from 6.5 J cm−3 for random nanocomposite film to 12.7 J cm−3 for coaxial electrospun film with medium polarization gradient. Finite element analyses reveal the polarization and local electric field distribution in the nanocomposites with various polarization gradient design, and the results unambiguously demonstrate that Ue can be significantly boosted via controlled polarization gradient design.

Thermal management of power electronics with liquid cooled metal foam heat sink

In this paper, a combined experimental and numerical study of liquid cooled aluminum foam (AF) heat sink applicable for high power electronics cooling was conducted. AF heat sinks with porosity (0.88) and pore densities (10 PPI and 20 PPI) are fabricated and the empty channel is employed for comparison. Experimental measurements were conducted subjected to non-Darcy flow regime. Numerical analysis was based on the Brinkman-Forchheimer extended Darcy momentum model, together with the energy equations of local thermal non-equilibrium (LTNE) and local thermal equilibrium (LTE) models. The permeability and inertia coefficient of the AF samples were correlated based on the measured pressure drop. New correlations of interfacial heat transfer coefficient between water and AF solid matrix were also determined. Numerically predicted local surface temperature and temperature field distributions were presented and validated with the experimental measurements. The results reveal that the permeability decreases and the inertial coefficient increases with increasing pore density. The thermal performance of AF heat sinks is appreciably superior to the empty channel, under a given flow rate, the Num of the AF heat sink can be 1.40–1.76 times of the empty channel. Heat transfer enhancement by 20 PPI foam is inappreciable, approximately 5%, compared to that of 10 PPI. The LTNE model demonstrates more accurate for predicting the spatial temperature distributions than the LTE model. The results also indicate that the non-equilibrium heat transfer phenomenon in water-cooled AF heat sink is not pronounced, and the non-equilibrium effect is declined with increasing velocity.

Absorption Reduction of Large Purcell Enhancement Enabled by Topological State-Led Mode Coupling.

We propose the mechanism of edge state-led mode coupling under topological protection; i.e., localized surface plasmons almost do not have any influence on the edge state, while the edge state greatly changes the local field distribution of surface plasmons. Based on this mechanism, in the well-designed topological photonic structure containing a resonant plasmon nanoantenna, an obvious absorption reduction in the spontaneous emission spectra appears due to the near-field deformation around the antenna induced by the edge state. Because a plasmon antenna with ultrasmall mode volume provides large Purcell enhancement and simultaneously the photonic crystal guides almost all scattering light into its edge state, the rate of nonscattering single photons reaches more than 10^{4}γ_{0}. This topological state-led mode coupling mechanism and induced absorption reduction, which are based on topological protection, will have a profound effect on the study of composite topological photonic structures and related micro- and nanoscale cavity quantum electrodynamics. Also, nonscattering large Purcell enhancement will provide practical use for on-chip quantum light sources, such as single-photon sources and nanolasers.

Design on orientation of one-dimensional ZnO/P(VDF-HFP) nanocomposites for significant enhanced electromechanical conversion

Flexible piezoelectric generators (PEGs) are receiving considerable attention due to the increasing demands on lightweight and sustainable power supply for wearable electronics. Combing piezoelectric nanofillers with polymers have been extensively investigated as a promising strategy. Here, piezotronic ZnO nanorods are introduced into poly (vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] considering that piezoelectric functions of both components can be united for high performance PEGs. ZnO/P(VDF-HFP) nanocomposites were designed with fillers distribution controlled via different processing, and the relationship between the filler orientation and the crystallization behaviors, dielectric and electromechanical conversion performances with respect to filler content were studied. The microcapacitor model and percolation theory were employed to understand the dielectric anisotropy in oriented nanocomposites, and furthermore, finite element analyses were utilized to reveal the distribution of local electric field. Finally, a maximum output voltage 11.8 V has been achieved in oriented ZnO/P(VDF-HFP) film, which is 2.3 times and 7.9 times the value of random nanocomposites (5.1 V) and pure P(VDF-HFP) film (1.5 V), respectively. With the piezoelectric responses obtained from piezoelectric force microscopy, significant enhancement in electromechanical conversion performance has been thoroughly discussed. The results thus demonstrate a promising strategy towards high-performance flexible piezoelectric generator.