Theoretical and Numerical Analysis of Active Switching for Narrow-Band Thermal Emission with Graphene Ribbon Metasurface

Components smaller than the wavelength of electromagnetic waves are called meta-atoms. Thermal emission can be controlled by an artificial structure in which these meta-atoms are arranged on the surface. This artificial structure is called a metasurface, and its optical properties are determined by the materials and shapes of the meta-atoms. However, optical devices may require active control of thermal emission. In the present study, we theoretically and numerically analyze a wavelength-selective emitter using a graphene ribbon metasurface. The graphene ribbon metasurface consists of a graphene ribbon array, potassium bromide thin film, and silver substrate. The geometric parameters of the graphene metasurface are determined based on an equivalent circuit model that agrees well with the results of the electromagnetic field analysis (rigorous coupled-wave analysis). The proposed emitter causes impedance matching depending on the conductivity of the graphene ribbon in a very narrow wavelength range. The conductivity of graphene can be actively controlled by the gate voltage. Therefore, the proposed emitters may realize near-perfect emission with a high quality factor and active controllable switching for various wavelengths. In addition, the quality factor can be changed by adjusting the electron mobility of graphene. The proposed emitter can be used for optical devices such as thermophotovoltaic systems and biosensing.

Design Pollution Gas Sensor Using Graphene Ribbon: Density Function Theory (DFT)

Density Function theory (DFT) calculation used to employed ground and excitation states for graphene ribbons, types of adsorption, energy gap, maximum wave length and optical band gap. Adsorption energy showed that CO2 gas molecule have chemical adsorption in distance 1 and 1.5 Angstrom, distance 2 and 2.5 Angstrom appear physical adsorption, adsorption energy decreased when distance between surface and gas molecule increasing. Resulting from chemical adsorption energy gap change with distance 1 and 1.5 Angstrom because attract gas molecule with surface. Excitation energy for nano system in sample 1 and 4 shifted to low wavelength (blue shift) change from 1018 nm to 993 nm and 718 nm on series. Other sample have red shift and energy gap becoming open. Result showed that graphene ribbon sense carbon dioxide gas (CO2).

Tunable Transmissive Terahertz Linear Polarizer for Arbitrary Linear Incidence Based on Low-Dimensional Metamaterials

In this work, we propose a structure consisting of three metamaterial layers and a metallic grating layer to rotate the polarization of arbitrary linearly polarized incidence to the y-direction with high transmissivity by electrically tuning these metamaterials. The transfer matrix method together with a harmonic oscillator model is adopted to theoretically study the proposed structure. Numerical simulation based on the finite difference time-domain method is performed assuming that the metamaterial layers are constituted by graphene ribbon arrays. The calculation and simulation results show that the Drude absorption is responsible for the polarization rotation. Fermi level and scattering rate of graphene are important for the transmissivity. For a polarization rotation of around 90°, the thickness of either the upper or lower dielectric separations influences the transmission window. For a polarization rotation of around 45° and 135°, the lower dielectric separations decide the frequency of the transmission window, while the upper dielectric separations just slightly influence the transmissivity.

Effects of A Magnetic Field on the Transport and Noise Properties of a Graphene Ribbon with Antidots

We perform a numerical simulation of the effects of an orthogonal magnetic field on charge transport and shot noise in an armchair graphene ribbon with a lattice of antidots. This study relies on our envelope-function based code, in which the presence of antidots is simulated through a nonzero mass term and the magnetic field is introduced with a proper choice of gauge for the vector potential. We observe that by increasing the magnetic field, the energy gap present with no magnetic field progressively disappears, together with features related to commensurability and quantum effects. In particular, we focus on the behavior for high values of the magnetic field: we notice that when it is sufficiently large, the effect of the antidots vanishes and shot noise disappears, as a consequence of the formation of edge states crawling along the boundaries of the structure without experiencing any interaction with the antidots.

Energy and Mode Filtering in a Graphene Channel With Unevenly Spaced Barriers with a Smooth Profile

We simulate the transport and shot noise behavior of graphene armchair ribbons with a series of parallel, unevenly spaced potential barriers with a smooth profile (which could result from the electrostatic effect of negatively biased gates). We analyze the effect of Klein tunneling and resonant tunneling on the individual modes propagating through the graphene channel, showing that this structure can behave as a mode and an energy filter for the charges injected from the contacts. Moreover, we study the different transport regimes (ballistic, strong localized, and diffusive) that can take place inside the graphene ribbon and the effect on the shot noise behavior of the device