Xibin Xu

Plasmonic Absorption Enhancement in Elliptical Graphene Arrays

In this paper, we come up with a wavelength tunable absorber which is made up of periodically elliptical graphene arrays in the far-infrared and terahertz regions. Through simulation, we find that we can increase the length of long axis of the ellipse, raise the incidence angles of TM- and TE-polarization (TM- and TE-polarization indicate the direction of the incident electric field along the direction of the x and the y axis, respectively.) within certain limits, and increase the chemical potential of graphene, so as to enhance the absorption of light in the elliptical graphene arrays. We also compare the absorption spectra of the original structure and the complementary structure, and find that the absorption of the original structure is higher than that of the complementary structure. In the end, we study the changes in the absorption rate of the double layer structure of the elliptical array with the increase in the thickness of SiO2. The elliptical array structure can be applied to tunable spectral detectors, filters and sensors at far-infrared and terahertz wavelengths.

Plasmonic absorption characteristics based on dumbbell-shaped graphene metamaterial arrays

Abstract In this paper, we proposed a theoretical model in the far-infrared and terahertz (THz) bands, which are dumbbell-shaped graphene metamaterial arrays with a combination of graphene nanobelt and two semisphere-suspended heads. We report a detailed theoretical investigation on how to enhance localized electric field and the absorption in the dumbbell-shaped graphene metamaterial arrays. The simulation results show that absorption characteristics can be changed by changing the geometrical parameters of the structure and the Fermi level of graphene . Furthermore, we have discovered that the resonant wavelength is insensitive to TM polarization. In addition, we also find that the double-layer graphene arrays have better absorption characteristics than single-layer graphene arrays. This work allows us to achieve tunable terahertz absorber and may also provide potential applications in optical filter and biochemical sensing.

Optical Properties and Local Electromagnetic Field Enhancement of Periodic Rectangular Nanohole Arrays in Au-Interlayer-Au Multilayer Films

The optical properties and the local electromagnetic field enhancement of a compound structure with rectangular nanohole arrays in Au-interlayer-Au multilayer films are numerically studied using finite-difference time domain method. We investigated some of structure parameters that influence the optical properties of the compound nanostructure. Adjustment of the length of rectangular nanoholes (L), the polarization direction (θ), the thickness of interlayer (SiO2, H2), and the materials in the interlayer can change the absorption intensity and the resonance peaks. An interlayer is located between the double Au films (Au-interlayer-Au multilayer films) with the function of confining local electromagnetic field. The simulation of the electromagnetic field distribution shows that the location of the local electromagnetic field enhancement can specify the different resonance patterns. The proposed compound nanostructure will be promising for application in portable nanoplasmonic multisensing and imaging.

Nanostrip-Induced High Tunability Multipolar Fano Resonances in a Au Ring-Strip Nanosystem

Surface plasmon resonances of a Au ring-strip nanosystem with tunable multipolar Fano resonances have been investigated based on the finite-difference time-domain (FDTD) method. Abundant plasmon properties of a Au ring-strip nanosystem can be obtained on the basis of the unique electronic properties of different geometry parameters. In our research models, these multipolar Fano resonances are induced and can be tuned independently by changing the geometry parameters of the Au ring-strip nanosystem. Complex electric field distributions excited by the Au ring-strip nanosystem provide possibility to form dark plasmonic modes. Multipolar Fano resonances display strong light extinction in the Au ring-strip nanosystem, which can offer a new approach for an optical tunable filter, optical switching, and advanced biosensing.

Multi-Scale Modeling for Predicting the Stiffness and Strength of Hollow-Structured Metal Foams with Structural Hierarchy

This work was inspired by previous experiments which managed to establish an optimal template-dealloying route to prepare ultralow density metal foams. In this study, we propose a new analytical–numerical model of hollow-structured metal foams with structural hierarchy to predict its stiffness and strength. The two-level model comprises a main backbone and a secondary nanoporous structure. The main backbone is composed of hollow sphere-packing architecture, while the secondary one is constructed of a bicontinuous nanoporous network proposed to describe the nanoscale interactions in the shell. Firstly, two nanoporous models with different geometries are generated by Voronoi tessellation, then the scaling laws of the mechanical properties are determined as a function of relative density by finite volume simulation. Furthermore, the scaling laws are applied to identify the uniaxial compression behavior of metal foams. It is shown that the thickness and relative density highly influence the Young’s modulus and yield strength, and vacancy defect determines the foams being self-supported. The present study provides not only new insights into the mechanical behaviors of both nanoporous metals and metal foams, but also a practical guide for their fabrication and application.