L-shaped Graphene Research Articles

Polarization-desensitization dynamically adjustable quintuple plasmon-induced transparency multi-frequency modulator based on graphene metamaterial

The monolayer metamaterial that consists of graphene arrangement squares and four L-shaped graphene blocks is designed to achieve quintuple plasmon-induced transparency (quintuple-PIT). First, the accuracy of the results has been validated through finite difference time domain simulations and coupled mode theory, which show good agreement. Second, a quadruple-frequency asynchronous switch with amplitude modulation degree (AMD) values of 94.7%, 91.1%, 96.6%, and 77.4% and a sextuple-frequency synchronous switch with AMD values of 95.0%, 96.8%, 88.0%, 93.3%, 58.6%, and 71.5% have been proposed by dynamic control, respectively. It is worth noting that the number of PIT windows in the transmission curve can be freely adjusted from a quintuple-PIT to single-PIT mode by manipulating the Fermi level states of different parts of the structure. Finally, further investigations have demonstrated that the proposed structure exhibits excellent slow-light properties and is insensitive to polarized light, which indicates that the metamaterial structure possesses good stability and anti-interference capabilities under various polarization conditions. The metamaterial and results provide valuable insights and ideas for the design of optoelectronic devices.

4 × 4 graphene nano-antenna array for plasmonic sensing applications

The manuscript presents the design and investigation of square and L-shaped graphene plasmonic nano-antenna arrays on a silicon dioxide substrate for plasmonic biosensing applications. The design parameters, such as the shape of the nanostructure, spacing between the antenna array elements, size of the antenna array and chemical potential of the graphene are used to analyze the plasmonic resonance characteristics of the proposed plasmonic nano-antenna array. Initially, dispersive characteristics of graphene, such as conductivity, permittivity and refractive index are analyzed using its chemical potential for the validation of the graphene material for plasmonic sensing applications. The proposed square and L-shaped nanopatch antenna structures are radiating at 30 THz with a reflection coefficient of -28.4 dB and − 44.6 dB respectively at 0.1 eV chemical potential. It is observed that graphene nanopatch antenna radiates at 30 THz, 115 THz and 176 THz at a chemical potential of 1.3 eV. Further, the study demonstrated that the designed square and L-shaped nano-antenna exhibit a gain of 3.52 dB and 9.51 dB respectively at 30 THz. The gain can be increased further using a square and L-shaped nano-antenna array of dimensions 2 × 2, 3 × 3 and 4 × 4. It is observed that maximum gains of 33.44 dB and 30.86 dB are obtained for the square and L-shaped 4 × 4 plasmonic nanoarray antenna respectively. Finally, a nanocircuit model of square and L-shaped nano-antennas is proposed and validated through CST simulations.

A plasmonic terahertz perfect absorber based on L-shaped graphene patches and gold rods

A plasmonic terahertz perfect absorber based on L-shaped graphene patches and gold rods

A quintuple plasmon-induced transparency multifunction switch based on the polarization-sensitive graphene-based metamaterial

A monolayer metamaterial consisting of a rectangle graphene strip and four L-shaped graphene blocks was proposed to achieve a quintuple plasmon-induced transparency (quintuple-PIT). The numerical simulation results based on the finite difference time domain method agree well with the calculated results of the coupled mode theory. By modulating the Fermi energy level of graphene, an octuple-frequency asynchronous switch and a sextuple-frequency synchronous switch are designed and studied, which have excellent amplitude modulation degree (up to 97.7%), extinction ratio (up to 16.41 dB), insertion loss (low to 5.4%), and dephasing time(low to 3.86 ps). Furthermore, the results show that the proposed metamaterials has polarization-sensitive characteristics due to their non-central symmetry. Further research shows that the group index is as high as 604 which has a good slow light effect and can be used for optical storage. Hence, the quintuple-PIT proposed structure in this paper has good application value in the expansion of multi-function optical switches and the research of high-quality optical memory.

Dual-band tunable and strong circular dichroism in a metal-graphene hybrid zigzag metasurface

Most active chiral metasurfaces operate in a single band and have an unidirectionally tunable circular dichroism (CD). Here, we propose a zigzag metasurface composed of a Z-shaped metallic strip and a L-shaped graphene strip to realize the dual-band tunable and strong CD. Two strong CD values of -0.88 and 0.88 are found at f1 = 0.86 THz and f2 = 1.23 THz, respectively. The strengths and resonant frequencies of these two CD signals can be tuned by varying graphene's Fermi energy (EF). Strikingly, the CD value at 0.86 THz undergoes a continuous adjustment in a large range from 0.79 to -0.88 when EF increases from 0.32 eV to 1.00 eV, implying that the proposed metasurface supports the switching of CD signal between on-, off- and reverse-states. Based on the strong CD signals, the capability of the metasurface as a biosensor to detect Avian Influenza viruses is demonstrated. This work will advance the development of broadband tunable chiral-optical devices.

A tunable circularly polarized antenna in THz regime

A transmissive type single layered tunable linear to circular polarization converter is realized by conglomerating both metallic and graphene patches on the same layer over a polyimide substrate. The tunability has been realized in the proposed metasurface by varying the chemical potential of the L-shaped graphene patches at the diagonal ends. Quadrature phase shift between the orthogonal components of the electric field is produced by the anisotropy caused by the double T-shaped copper patch. A tunable axial ratio (≤3 dB) bandwidth ranging from 2.57 to 3.06 THz is exhibited. To demonstrate the polarization conversion capability of the proposed tunable polarization converter (PC), a linearly polarized microstrip patch antenna (MSA) operating in the same frequency band has been designed and integrated with it. The radiated linearly polarized electromagnetic waves from the antenna get transformed into circularly polarized waves after passing through the PC. Thus, a circularly polarized antenna is realized whose 3-dB axial ratio bandwidth is tunable across 2.6–3 THz. The transmissive type PC has been placed 10 μm above the antenna to generate left-hand circularly polarized (LHCP) waves across a bandwidth of 400 GHz. The proposed simple structured linear to circular PC provides the advantage of dynamic regulation of the CP band without making any alteration in the physical structure of the antenna. Most of the reported CP antennas in THz range constitute graphene based radiating patches. They do not involve the use of metasurface for polarization conversion. For the first time, the PC integrated microstrip patch antenna has been analyzed in this work. The principle of polarization conversion has been numerically studied through full-wave simulations in CST.

Tunable wide-angle multi-band mid-infrared linear-to-linear polarization converter based on a graphene metasurface* *Project supported by the School Youth Fund of Henan University of Science and Technology (Grant No. 2014QN045).

We present a high-efficiency tunable wide-angle multi-band reflective linear-to-linear (LTL) polarization converter, which is composed of an array of two L-shaped graphene patches with different sizes. In the mid-infrared region, the proposed converter can transform x-polarized wave into y-polarized wave at four resonant frequencies. The polarization conversion ratios of the four bands reach 94.4%, 92.7%, 99.3%, and 93.1%, respectively. By carefully choosing the geometric parameter, triple-band LTL polarization conversion can also be realized. The three polarization conversion ratios reach 91.50%, 99.20%, and 97.22%, respectively. The influence of incident angle on the performances of the LTL polarization converter is investigated, and it is found that our polarization converter shows the angle insensitivity. Also, the dynamically tunable properties of the proposed polarization converter are numerically studied by changing Fermi energy. All the simulation results are conducted by finite element method.

Fabrication of fanlike L-shaped graphene nanostructures with enhanced thermal/electrochemical properties via laser irradiation

Engineering can be used to create uniquely oriented 2D materials, especially graphene, and can play a crucial role in the development of multifunctional films for applications in supercapacitors and thermal management, imparting excellent electrical and thermal properties to the films. However, the preparation of a uniquely structured graphene film with high-quality often requires a complex multi-step technique. Herein, we propose a facile and efficient one-step laser irradiation process for the synthesis of multifunctional laser-induced graphene electrodes consisting of L-shaped reduced graphene oxide nanosheets with vertical alignment (VrGO). Notably, the instantaneous high thermal energy of the laser irradiation can heal the defects of graphene oxide (GO) nanosheets, thus, enhancing the electrical conductivity and crystallinity while inducing the vertical alignment. Additionally, the vertical alignment of high-quality GO nanosheets leads to more isotropic thermal transport, thus, enhancing the out-of-plane thermal conductivity to 6.202 W m−1K−1. GO nanosheets also exhibited superior performances as supercapacitor electrodes, demonstrating an outstanding areal capacitance of 36.8 mF cm−2 at 1.2 mA cm−2, and excellent stability up to 10,000 cycles of charging/discharging. This simple laser technique opens up new possibilities for engineering the structural and physical properties of graphene for applications in various fields that require functional thin films.

Multi-band multi-tunable perfect plasmon absorber based on L-shaped and double-elliptical graphene stacks

In this paper, a multi-band multi-tunable graphene absorber structure is proposed. The absorber is made by “+” intersecting double-ellipse graphene, L-shaped graphene layer, medium layer, the metal layer, and Si substrate. By using this structure, we investigated the possibility of graphene surface plasmon resonance in the incident far-infrared wave and THz wave range. For this structure, we use the FDTD Solution of finite time domain difference software to conduct theoretical research on it. The results show that the absorbing device in the range of the infrared in λ1 = 10.78 μm, λ2 = 12.20 μm and λ3 = 21.74 μm show perfect absorption peak of absorption rate is as high as 99.97%、99.81% and 99.91%, respectively. By controlling the Fermi level or the geometric parameters of the graphene layer can dynamically adjust the resonant wavelength of absorbing device, and polarization insensitivity characteristics. And in TE or TM mode, it can maintain good absorption performance in a wide range of 0° ~ 60°. We believe that our research results will open new doors for the use of metamaterial absorbers with multi-band, multi-tunable, polarization-independent and insensitive to large-angle oblique incidence. In the future, it can be used in photoelectric detection, photovoltaic cells, photoelectric sensors, photoelectric thermal radiation and other fields.

Polarization-insensitive ultra-broadband mode filter based on a 3D graphene structure buried in an optical waveguide

We propose a polarization-insensitive ultra-broadband mode filter based on a 3D graphene structure buried in a few-mode optical waveguide. Our experimental device fabricated by burying an L-shaped graphene structure in a three-mode polymer waveguide provides polarization-insensitive filtering of the fundamental mode, while keeping the higher-order modes, with a mode extinction ratio of ∼ 17 d B over the S + C + L band and beyond.

High operative polarization converter using metasurface consisted of dual reciprocal L-shaped graphene array

A single layer dual L-shaped graphene metasurface is presented to achieve a high operative and tunable polarization converter in the mid-infrared regime. The proposed device and numerical results indicate that linearly polarized wave can be converted to its cross-polarized wave. In addition, it can be used as a converter to a circularly polarized wave. This converter is insensitive to the angle of incident wave. Working frequencies can be easily and significantly tuned within a wide frequency range by regulating the chemical potential of the graphene. The physical procedure of the polarization conversion effect is explicated via coupling of the electric field components with various plasmon resonance modes of the metasurface. The suggested structure can pave a way to development of controllable plasmonic polarization converter systems for optical communication applications.

Tunable Dual-Band Perfect Absorber Based on L-Shaped Graphene Resonator

We propose and investigate a tunable dual-band perfect absorber consisting of double asymmetric L-shaped graphene resonators (LSGRs) and a metal ground plane spaced by a thin SiO2 dielectric layer. The numerical results reveal that the presented absorber expresses two resonance peaks in the mid-infrared region, where their absorption coefficients are on average larger than 98.77%. The electromagnetic eigenmode resonances of a single LSGR can induce two absorption peaks with values about 50%. Assembling two LSGRs together, the absorptivity can reach up to almost 100% due to the plasmonic couplings. In addition, the design has the ability to tune the working wavelengths of the absorption peaks within a large wavelength range by changing geometric parameters and the Fermi level of the graphene layer. In addition, wavelength-selective dual-band perfect absorption peaks can be achieved in the wavelength range of interest by merely adjusting the polarization angle. This letter presents a unique route toward the realization of nanophotonic devices and has potential applications in filtering, sensing, and detecting.

Triple-band cross-polarization converter based on an ultra-thin graphene-integrated metasurface

We propose a triple-band, tunable, and highly efficient reflected cross-polarization converter in the mid-infrared. The converter is composed of a metal ground plane, a dielectric layer, and double L-shaped graphene patch arrays. Triple bands (36.15, 48.95, and 52.20 THz) of cross-polarization conversion are achieved due to the superimposition of the two reflected components with a near 180° phase difference. The tunable performance of our proposed converter can be realized by changing the Fermi energy and electron scattering time. Our idea is verified by finite element method simulation and paves a way to the design of multi-band polarization converters.

Graphene Logic Gates

Graphene is a biocompatible material that can be incorporated safely into living tissue. This property makes graphene an ideal material for bioelectronics applications. The main obstacle for using graphene as a material for bioelectronic circuits is the lack of a bandgap, which results in noneffective current switching. Here, we use rectangular L-shaped graphene nanoribbons as a building block for graphene logic gates. Electrons are initially transported along the zigzag-edged nanoribbon and then the transport direction changes by 90°, resulting in transport along the armchair edge. Our computations showed that electron scattering because of this change in the direction causes the appearance of a pseudobandgap, which is large enough for logic operations. This pseudobandgap appears as a zero-conductance region for electron energies near the Fermi level. We propose an and , an or, and a not logic gate and use tight-binding Hamiltonians and nonequilibrium Greens functions to show that these designs can reproduce effectively the desired logic operations.

Conductance of L-shaped and T-shaped graphene nanoribbons

Rectangular graphene nanoribbons with two contacts have been studied extensively as parts of several nanoelectronic devices. L-shaped and T-shaped graphene nanoribbons received a little or no attention until now. In this letter, we present computations of the conductance of L-shaped graphene nanoribbons with two contacts and of T-shaped graphene nanoribbons with tree contacts. We used tight-binding Hamiltonians and non-equilibrium Green's functions to compute their conductance. In L and T-shaped nanoribbons electrons are initially transported along a zigzag-edged nanoribbon, and then the direction of their motion changes by 90O and are transported along an armchair-edged nanoribbon. Our results show that this change in direction of motion results in a zero-conductance region that extents about 0.25 eV below and above the Fermi level. This zero conductance region is large enough to cause current switching and, because of this, L and T-shaped graphene nanoribbons can be used as building blocks for logic gates.

Broadband polarizers based on graphene metasurfaces.

We present terahertz metasurfaces based on aligned rectangular graphene patches placed on top of a dielectric layer to convert the transmitted linearly polarized waves to circular or elliptical polarized radiation. Our results lead to the design of an ultrathin broadband terahertz quarter-wave plate. In addition, ultrathin metasurfaces based on the arrays of L-shaped graphene periodic patches are demonstrated to achieve broadband cross-polarization transformation in reflection and transmission. The proposed metasurface designs have tunable responses and are envisioned to become the building blocks of several integrated terahertz systems.

Dynamic conductance in L-shaped graphene nanosystems

Dynamic conductance of nanocircuit, which demonstrates dc and ac transport properties, is regarded as vital indicator for device feature. With the help of nonequilibrium Green's function technology and Buttiker's ac transport theory, we present dynamic conductance in L-shaped graphene nanosystems (LGNSs). It is found that electronic transport is highly sensitive to the geometric feature as well as the size of LGNSs. The armchair edge lead determines whether LGNS shows ac response or not around Dirac point. The increase of width of zigzag edge lead suppresses dc conductance and induces capacitive responses at the anti-resonance states. This is due to large dwell time originated from edge state in zigzag edge lead. In the energy region far away from Dirac point, LGNS responds inductively with the transportation channel opens. Behaviors of dynamic conductance at Dirac point and anti-resonance states are discussed by interesting spacial-resolved local density of states.

Mid-Infrared Tunable Dual-Frequency Cross Polarization Converters Using Graphene-Based L-Shaped Nanoslot Array

In this paper, we proposed a novel dual-frequency cross polarization converter that can simultaneously work at two frequencies in the reflection mode, which is constructed of an L-shaped perforated graphene sheet printed on a dielectric material backed by a gold ground plane. For the normal incidence, the optical rotation at these two working frequencies originates from the simultaneous excitation of both eigenmodes that are characterized as the results of the localized surface plasmon resonances. Moreover, by merely varying the Fermi energy of the graphene, both working frequencies can be tuned within a large frequency range, which suggests numerous potential optical applications.

Dynamically tunable broadband mid-infrared cross polarization converter based on graphene metamaterial

We present a mid-IR highly wavelength-tunable broadband cross polarization conversion composed of a single patterned top layer with L-shaped graphene nanostructures, a dielectric spacer, and a gold plane layer. It can convert linearly polarized light to its cross polarization in the reflection mode. The polarization conversion can be dynamically tuned and realize a broadband effect by varying the Fermi energy without reoptimizing and refabricating the nanostructures. This offers a further step in developing the tunable polarizers and the polarization switchers.

Electron Transport of Right-Angle Graphene Nanoribbons

By the tight-binding method, we study the transport properties of right-angle L-shaped graphene nanoribbons. We found a universal conclusion is that the resonance of electron tunneling will present at the Dirac point when the system is metallic and the ribbons widths satisfy (NBAB=2NBZB-1). Further research suggests that the conductance resonance effect will be destroyed by impurity scatterer, especially the impurity concentration and strength are nontrivially large. We also found that antiresonance effect will result in a strong conductance suppression when the width difference () of the two ribbons is very big. In addition, when the system is semiconducting, the center of the well-defined insulating band can be easily tuned by a gate bias exerted on the armchair-edged graphene nanoribbon.