Chemical Potential Of Graphene Research Articles

Generating terahertz multiple vortex beams using graphene metasurfaces

This paper investigates the generation of orbital angular momentum vortex beams using a graphene metasurface in the terahertz frequency band. The proposed design consists of 20 × 20 unit-cell elements to operate in 1.2 THz applications. Each element is a graphene ring patch printed on a silicon dioxide substrate backed with a polysilicon ground plane of size 75 × 75 × 25 µm3. The graphene reconfigurable surface conductivity is used to control the beam shape, direction, and directivity radiated from the metasurface, through the application of DC biasing voltages. A parametric study on the effect of graphene chemical potential, relaxation time and temperature on the unit-cell reflection properties is introduced. The reflection magnitude varies from − 2.1 dB to -0.8 dB with a 350-degree phase variation for µc ranging from 0.25 eV to 1.6 eV at \\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\ au$$\\end{document} =5 ps, and T = 300 K. The effect of graphene relaxation time from 0.3 ps to 10 ps on the reflection coefficient at µc = 0.7 eV, and T = 300 K is investigated. The metasurface radiation characteristics are investigated under the illumination of two types of incidence sources, plane-wave, and focused-waves. A depiction of a single vortex beam in various orientations θ = 0, 30o, 50o, and 70o, φ = 90o for l = 1 is presented. The purity of the OAM single beam shows that 94% of the power is concentrated in the designed mode. A graphene metasurface can to convert linearly polarized input into multiple beams exhibiting orthogonal modes. Two/four vortex beams in different directions are demonstrated. The capacity for wireless communication in the terahertz band can be enhanced by utilizing a graphene metasurface.

Controlled circular dichroism with graphene-based metamaterial for terahertz wave

This article explores the design and analysis of a metal-graphene hybrid metamaterial structure tailored for tunable circular dichroism (CD) effects in the terahertz (THz) frequency regime. Chiral metamaterials have garnered considerable interest in photonics due to their versatile applications, including sensing, polarization manipulation, and chiral imaging. The proposed metamaterial unit cell features four meta-atoms with C4 rotational symmetry, composed of gold on a polyimide substrate. By strategically integrating the graphene sheets above the gold patterns, selective control over the absorption efficiency for the incident wave of left-handed circularly polarized (LCP) and right-handed circularly polarized (RCP) light is achieved. The study demonstrates that adjusting graphene chemical potential enables precise modulation of CD from 0.80 to 0.10 across a wide THz frequency spectrum. Furthermore, the article investigates the structure optical response for incident angles ranging up to 75°, revealing stable CD behavior up to 30° and intriguing dual-band effects beyond 50°. These findings underscore the potential of the proposed metamaterial for practical applications in photonics, sensing, and chiral imaging, offering tunable control over the CD effects in the THz regime.

Efficient and high-quality absorption enhancement using epsilon-near-zero cylindrical nano-shells constructed by graphene

This paper presents a detailed scattering analysis of a hollow-core plasmonic-shell cylindrical wire to design an efficient, compact, narrowband, and reconfigurable optical absorber. The shell is formed by a thin graphene material, investigated in its epsilon-near-zero (ENZ) plasmonic region. Compared to the graphene plasmonic resonances in the terahertz(THz)/far-infrared (FIR) frequencies, the ENZ plasmonic resonances offer a blue shift in the operating frequency of the second-order plasmonic resonances by increasing the geometrical dimensions. This feature is successfully used to design efficient optical wave absorbers with absorption cross-sections much larger than geometrical and scattering cross-sections. The observed blue shift in the resonance spectrum, which is the key point of the design, is further verified by defining each particle with its polarizability and fulfilling the resonant scattering condition in the framework of Mie’s theory. Furthermore, graphene relaxation time and chemical potential can be used to manipulate the absorption rate. Observed resonances have narrow widths, achieved with simple geometry. To consider more practical scenarios, the one-dimensional arrangement of the cylindrical elements as a dense and sparse array is also considered and the design key point regarding graphene quality is revealed. The quality factor of the sparse array resonance is 2272.8 and it demands high-quality graphene material in design. It is also observed that due to the use of small particles in the design, the near-field and cooperative effects are not visible in the absorption cross-section of the array and a clear single peak is attained. This polarization-insensitive absorber can tolerate a wide range of incident angles with an absorption rate above 90%.

Electrically tunable virtual image Luneburg lens using graphene.

Virtual image lenses play essential roles in various optical devices and applications, including vision correction, photography, and scientific instruments. Here, we introduce an approach for creating virtual image Luneburg lenses (LL) on graphene. Remarkably, the graphene plasmonic lens (GPL) exhibits electrically tunable virtual focusing capabilities. The design principle of the tunability is based on the nonlinear relationship between surface plasmon polariton (SPP) wave mode index and chemical potential of graphene. By controlling the gate voltage of graphene, we can achieve continuous tuning of virtual focus. A ray-tracing technique is employed to determine the required gate voltages for various virtual focal lengths. The proposed GPL facilitates adjustable virtual focusing, promising advancements in highly adaptive and transformative nanophotonic devices.

Tunable broadband terahertz graphene metasurface for complex-amplitude vortex beam generator and hologram

The independent controls of phase and amplitude, known as complex-amplitude modulation, play a crucial role for modulating the electromagnetic wavefronts. In this paper, a tunable broadband terahertz (THz) graphene metasurface with complex-amplitude modulation is proposed. A novel hybrid modulation mechanism that combines the absorption, polarization conversion, and Pancharatnam–Berry (PB) phase is employed to achieve a wide complex-amplitude modulation range over a broad frequency band. In addition, the metasurface can be dynamically tuned from the electrically tunable nature of the graphene in the THz range. To reveal the tunability characteristics of the metasurface as the graphene chemical potential varies, we study the Kubo formula of the graphene conductivity model and combine it with the equivalent circuit model. Two THz graphene meta-devices are designed for complex-amplitude vortex beam generator and hologram. By varying the graphene chemical potentials of 0 and 1 eV as the ON and OFF states, a THz quad-vortex-beam generator with switchable modes is designed and verified. We also demonstrate a THz hologram with complex-amplitude modulation by adjusting the chemical potential, exhibiting low imaging noise and high image quality. The proposed method is promised to be applied to the design of more complex-amplitude THz graphene meta-devices.

Nonequilibrium Casimir–Polder Force between Nanoparticles and Graphene-Coated Silica Plate: Combined Effect of the Chemical Potential and Mass Gap

The Casimir–Polder force between spherical nanoparticles and a graphene-coated silica plate is investigated in situations out of thermal equilibrium, i.e., with broken time-reversal symmetry. The response of the graphene coating to the electromagnetic field is described on the basis of first principles of quantum electrodynamics at nonzero temperature using the formalism of the polarization tensor in the framework of the Dirac model. The nonequilibrium Casimir–Polder force is calculated as a function of the mass-gap parameter, the chemical potential of graphene, and the temperature of the graphene-coated plate, which can be both higher or lower than that of the environment. It is shown that the force value increases with the increasing chemical potential, and this increase is more pronounced when the temperature of a graphene-coated plate is lower than that of the environment. The nonequilibrium force also increases with increasing temperature of the graphene-coated plate. This increase is larger when the plate is hotter than the environment. The effect is revealed that the combined impact of the chemical potential, μ, and mass gap, Δ, of the graphene coating depends on the relationship between Δ and 2μ. If 2μ>Δ, the magnitude of the nonequilibrium force between nanoparticles and a cooled graphene-coated plate becomes much larger than for a graphene coating with μ=0. The physical reasons explaining this effect are elucidated. Possible applications of the obtained results are discussed.

Polarization and incident angle independent multifunctional tunable terahertz metasurface based on graphene

Motivated by the imperative demand for design integration and miniaturization within the terahertz (THz) spectrum, this study presents an innovative solution to the challenges associated with singular functionality, limited application scope, and intricate structures prevalent in conventional metasurfaces. The proposed multifunctional tunable metasurface leverages a hybridized grapheme–metal structure, addressing critical limitations in existing designs. Comprising three distinct layers, namely a graphene–gold resonance layer, a Topas dielectric layer, and a bottom gold film reflective layer, this terahertz metasurface exhibits multifunctionality that is both polarization and incident-angle independent. The metasurface demonstrates a broadband circular dichroism (CD) function when subjected to incident circularly polarized waves. In contrast, under linear incidence, the proposed design achieves functionalities encompassing linear dichroism (LD) and polarization conversion. Remarkably, graphene's chemical potential and the incident light’s state can be manipulated to tune each functional aspect's intensity finely. The proposed tunable multifaceted metasurface showcases significant referential importance within the terahertz spectrum, mainly contributing to advancing CD metamirrors, chiral photodetectors, polarization digital imaging systems, and intelligent switches.

Multi-channel graphene-based perfect absorbers utilizing Tamm plasmon and Fabry-Perot resonances.

In this paper, a multi-channel narrowband absorption structure utilizing the Tamm plasmon and Fabry-Perot resonances in the 1-2 THz range is presented. The structure consists of a graphene sheet, followed by a spacer layer and a dielectric-metal photonic crystal. The transfer matrix method (TMM) is employed to evaluate the effect of different parameters such as the constituent materials and thicknesses of the layers as well as the graphene chemical potential on the spectral response of the structure. Simulation results show that the number of channels, resonance frequencies, and absorption peaks can be easily adjusted by controlling the thicknesses and materials of the layers. The absorption value can reach as high as 99.23% for normal incidents. Additionally, perfect absorption of 100% is achievable by changing the angle of the incident light. Owing to high absorption and straightforward fabrication process, the proposed structure can find various applications such as filtering, sensing, optical switches, and thermal emissions.

Strong enhancement of near-field radiative heat transfer between anisotropic magneto-optical gratings by a weak magnetic field

The highly tunable surface magneto-plasmon polaritons supported by magneto-optical materials provide reliable means for active adjusting of near-field radiative heat transfer (NFRHT). In our study, we proposed an anisotropic system consisting of two graphene-covered magneto-optical gratings, and theoretically investigate the NFRHT between them controlled by a weak magnetic field. We find that an external magnetic field open a broad-spectrum photo tunneling channel and modify the energy distribution of surface electromagnetic modes in the wave-vector space. The near-field heat flux between two magneto-optical gratings can achieve a remarkable maximum enhancement of 6 times at the magnetic field H=0.9T compared to that without a magnetic field. Owing to the coupling between highly tunable surface magneto-plasmon polaritons of graphene and surface modes of InSb, the regulation ratio of the heat flux exceeds 10 from 0.5 T to 0.9 T. In addition, the effects of the separation distance, chemical potential of graphene and structural configuration of two gratings are also investigated. We look forward to the proposed system being used as a thermal switch, providing convenience for tuning thermal radiation and improving the efficiency of energy-utilization devices.

Design and investigation on polarization insensitive dual band graphene based tunable absorber for THz applications

In this communication, a metal-free graphene-based Absorber is designed and examined in the THz regime. The graphene layer is coated over the SiO2 substrate, while the silver layer is used on the other side of the substrate. The designed absorber works in two frequency bands i.e. 2.2–2.91 THz (11–14 μm) and 4.85–5.83 THz (51–62 μm), having more than 90% absorption. Peak absorption is obtained 2.55 THz and 5.05 THz with 97.78% and 99.71% absorption. With the help of circular sectoring, the designed absorber shows wide polarization and wide incident angle (up to 60°) insensitivity for both TE and TM modes. Change in chemical potential of graphene provides the tunable characteristics in the designed absorber. All these outcomes confirm that the designed metal-free graphene-based metamaterial absorber works efficiently in THz regime and can be used in different applications such as, sensing and imaging.

Graphene-based plasmonic nanoantenna with trapezoidal structure in THz band

Mainly manipulating emitted waves via plasmonic resonance is a fundamental characteristic of optical antennas. Plasmonic nanoantennas are used for terahertz (THz) radiation caused by optical interaction with surface resonance. The designed nanoantenna is such that the plasmonic resonance of the nanoantenna changes by controlling the graphene chemical potential (μc) from 0 eV to 0.2 eV. Although a dielectric layer separates the trapezoidal graphene sheets, an essential difference in the scattering parameters and the radiation pattern is observed since an external direct current bias changed the graphene surface impedance to about 860 Ω, which is the optimal value for reducing return loss in nano-systems. In other words, the plasmonic resonance frequencies can be tuned by the effect of a localised electrostatic field. Also, the trapezoidal graphene-based plasmonic nanoantenna has a high quality factor (Q-factor) from 2.35 to 5.71. Therefore, dynamic control, enhancing the input impedance and stable efficiency of graphene-based plasmonic nanoantennas, improves performance and matching at THz nano-systems for many applications of optoelectronic devices.

Frequency tunable switching between transmission and absorption modes based on graphene and VO2 layers at the THz range

In this paper, a tunable multilayer structure is proposed, which can provide reversible switching between transmission and absorption modes at the terahertz region without reconfiguration. The layered structure consists of graphene, Si, and VO2 layers. Transfer matrix method is employed to describe the optical properties of the layered structure. The switching phenomenon occurs based on the VO2 transition from insulator to metal phase by varying temperature. Furthermore, active frequency tuning by graphene chemical potential for thermally switching transmission and absorption with near-perfect intensity is observed. Incidence angular stability for TE and TM is up to 20° and 40°, respectively. Finally, the Si layer thickness effect demonstrates that mainly defines the peak number and frequency for both functions. Theoretical implementation confirms the potential usefulness of the proposed configuration in applications such as reversibly tunable smart absorbers, filters, or thermo-optical switches for high-speed optical systems.

Multiple surface polariton-enhanced near-field radiative heat transfer between layered graphene/porous SiC terminals

Near-field radiative heat transfer (NFRHT) between two separated terminals can enhance the heat flux determined by blackbody theory by several orders of magnitude. In this work, we study the NFRHT between two terminals made of periodic multilayered graphene/porous silicon carbide (SiC), specifically focusing on the multiple surface polariton effects. The two terminals are parallel and separated by a vacuum gap. The porous SiC-supported surface phonon polaritons (SPhPs) and hyperbolic phonon polaritons (HPhPs), and their coupling with the graphene-supported surface plasmon polaritons (SPPs) leads to apparent enhancement of the radiative heat flux between the gapped terminals. The underlying mechanism of multiple polaritons for amplifying the near-field heat flux is revealed through the energy transmission coefficients for different scenarios. Results show that the heat flux between the multilayered terminals is a combination result of the multiple surface polaritons and the medium loss. When the vacuum gap is set as d = 10 nm, the heat flux between the 50-layered terminals is 1.48 times that between the single-layered terminals. We demonstrate that the NFRHT can be dynamically controlled and optimized by appropriately engineering the number of layers, the chemical potential of graphene, and the porosity and thickness of the porous SiC sheet. This work paves an alternative controllable structure for strengthening and regulating NFRHT and thus has potential applications in micro-nanoscale thermal management.

Tunable dynamic metamaterial for negative refraction

The effective ability to manipulate the negative refraction behaviors of electromagnetic waves in the terahertz (THz) frequency range is of great interest for various practical applications in communication, imaging, and sensing. In this study, we propose a robust graphene-integrated metamaterial design for the dynamic manipulation of negative refraction at terahertz frequencies. Using the distinctive characteristics of graphene combined with the specially designed metamaterial structure, we demonstrated the active control of negative refraction by modulating the graphene's chemical potential from 0.0 to 1.0 eV. By dynamically tuning the carrier density of graphene, we create the switchable states of the negative index for the transmission or the reflection modes, tailoring the terahertz wave behavior in real time. In particular, in the case of different applied temperatures (through the bias applied voltages) of the proposed metamaterial, these two modes are maintained over 60% for both reflection and transmission while preserving the negative refractive index. Our results reveal the tunability of negative refraction, paving the way for developing reconfigurable THz meta-devices with enhanced functionalities in the near future.

Hexagonal-shaped graphene quantum plasmonic nano-antenna sensor

In this manuscript, a hexagonal-shaped graphene quantum plasmonic nanopatch antenna sensor is designed and investigated on silicon dioxide, zinc oxide and silicon substrates for quantum plasmonic biosensing applications. The optical properties of graphene are demonstrated using Kubo modeling to analyze the plasmon resonance characteristics of the nanopatch antenna. Nano-circuit modeling of the hexagonal-shaped graphene nano-antenna is proposed and validated using CST simulations. The parametric analysis of the hexagonal-shaped nanopatch antenna is performed using design parameters such as R (radius of the hexagon), Tp (thickness of the hexagon) and µc (chemical potential of graphene) to obtain optimum characteristics suitable for quantum plasmonic sensing applications. The study demonstrates that the proposed hexagonal-shaped nano-antenna exhibits gain of 4.9 dBi, 2.46 dBi, 14.99 dBi, 8.25 dBi, 5.15 dBi, 10.87 dBi and 2.4 dBi at 29.87 THz, 30 THz, 35 THz, 113.5 THz, 132.5 THz, 85 THz and 24 THz, respectively. The field enhancement factors observed at these frequencies are 794, 779, 584, 255, 234, 654 and 217, respectively.

Active anisotropic polarization conversion meta-surface for 6G communication bandgap in the reflection mode

This paper investigates a single-layered active anisotropic meta-surface design capable of achieving high polarization conversion efficiency in the 6 G communication band gap. Additionally, the designed structure can convert the linear polarization of the incoming wave fronts to its cross-polarization and linear polarization to circular polarization in the reflection mode. The polarization conversion characteristic is achieved due to the strong anisotropic behavior of the meta-surface. Such a simple design can achieve a 90% to 100% cross-polarization conversion efficiency over a frequency region of [0.28–0.36] THz. The linear to circular polarization conversion is performed near 0.26 THz and 0.40 THz. Between these two frequencies, band linear to cross-polarization conversion is more prominent. The proposed design can be tuned from a half-wave plate (HWP) or linear polarization converter to a quarter-wave plate (QWP) or circular polarization converter using the chemical potential of graphene. The optical response of the meta-surface behaves differently from different incident angles. The proposed polarization converter can contribute to the development of active polarization device.

Highly sensitive label-free biosensor: graphene/CaF2 multilayer for gas, cancer, virus, and diabetes detection with enhanced quality factor and figure of merit

One of the primary goals for the researchers is to create a high-quality sensor with a simple structure because of the urgent requirement to identify biomolecules at low concentrations to diagnose diseases and detect hazardous chemicals for health early on. Recently graphene has attracted much interest in the field of improved biosensors. Meanwhile, graphene with new materials such as CaF2 has been widely used to improve the applications of graphene-based sensors. Using the fantastic features of the graphene/CaF2 multilayer, this article proposes an improvement sensor in the sensitivity (S), the figure of merit (FOM), and the quality factor (Q). The proposed sensor is based on the five-layers graphene/dielectric grating integrated with a Fabry–Perot cavity. By tuning graphene chemical potential (µc), due to the semi-metal features of graphene, the surface plasmon resonance (SPR) waves excited at the graphene/dielectric boundaries. Due to the vertical polarization of the source to the gratings and the symmetry of the electric field, both corners of the grating act as electric dipoles, and this causes the propagation of plasmonic waves on the graphene surface to propagate towards each other. Finally, it causes Fabry–Perot (FP) interference on the surface of graphene in the proposed structure's active medium (the area where the sample is located). In this article, using the inherent nature of FP interference and its S to the environment's refractive index (RI), by changing a minimal amount in the RI of the sample, the resonance wavelength (interferometer order) shifts sharply. The proposed design can detect and sense some cancers, such as Adrenal Gland Cancer, Blood Cancer, Breast Cancer I, Breast Cancer II, Cervical Cancer, and skin cancer precisely. By optimizing the structure, we can achieve an S as high as 9000 nm/RIU and a FOM of about 52.14 for the first resonance order (M1). Likewise, the remarkable S of 38,000 nm/RIU and the FOM of 81 have been obtained for the second mode (M2). In addition, the proposed label-free SPR sensor can detect changes in the concentration of various materials, including gases and biomolecules, hemoglobin, breast cancer, diabetes, leukemia, and most alloys, with an accuracy of 0.001. The proposed sensor can sense urine concentration with a maximum S of 8500 nm/RIU and cancers with high S in the 6000 nm/RIU range to 7000 nm/RIU. Also, four viruses, such as M13 bacteriophage, HIV type one, Herpes simplex type 1, and influenza, have been investigated, showing Maximum S (for second resonance mode of λR(M2) of 8000 nm/RIU (λR(M2) = 11.2 µm), 12,000 nm/RIU (λR(M2) = 10.73 µm), 38,000 nm/RIU (λR(M2) = 11.78 µm), and 12,000 nm/RIU (λR(M2) = 10.6 µm), respectively, and the obtained S for first resonance mode (λR(M1)) for mentioned viruses are 4740 nm/RIU (λR(M1) = 8.7 µm), 8010 nm/RIU (λR(M1) = 8.44 µm), 8100 nm/RIU (λR(M1) = 10.15 µm), and 9000 (λR(M1) = 8.36 µm), respectively.

Near-field thermal rectification via an InSb/graphene/3C–SiC-nanowire heterostructure

Thermal rectifiers allow asymmetric heat flux when the temperature bias between two terminals is reversed. Based on the near-field radiative heat transfer, the performance of thermal rectifiers can be significantly enhanced. Here, we propose a near-field thermal rectifier based on the InSb/graphene/3C–SiC-nanowire heterostructure. The rectifier consists of two terminals, one terminal is an InSb slab with a graphene-coated bottom, and the other terminal is a 3C–SiC nanowire array with a graphene cover on its top. By using fluctuational electrodynamics, we calculate the radiation heat flux and the corresponding thermal rectification efficiency (TRE). The results show that the strong asymmetric surface plasmon polaritons (SPPs) and hyperbolic phonon polaritons (HPPs) in the forward and reverse heat transfer scenarios guarantee a robust TRE. Besides, the TRE of the proposed heterostructure can be dynamically controlled and optimized via the chemical potential of graphene, the volumetric filling ratio of the nanowire array, and the terminal temperature. Specifically, the thermal rectification efficiency (1 – min (Qf, Qr)/max (Qf, Qr) with Qf and Qr denoting the forward and reverse heat flux, respectively) can exceed 80% at a wide-ranged terminal gap and reaches a maximum of 92.96%.

Reconfigurable graphene-based multi-input multi-output antenna design for THz applications

This paper presents a compact graphene-based multi-input multi-output (MIMO) antenna for wireless communications operating in frequency band (0.1-10) THz. This work has been performed with four ports microstrip antennas based on 37×88 μm² a silicon dioxide (Sio₂) substrate and copper on the ground layer, with high isolation by a series of unit cells of graphene selected between adjacent patches to reduce the transmission coefficient and antenna size. Graphene's chemical potential will change by changing the connected DC voltage, leading to bandwidth and resonant frequency variation. The simulation has a reflection coefficient is less than -10 dB at (4.5-10) THz of the frequency scale, mutual coupling (-15 dB), and the gain from (4.7-9) THz is (1.6-6.7254) dB. This paper aims to provide wideband, efficient and reconfigurable with simple graphene-based MIMO antenna for THz applications.

Reconfigurable graphene-based multi-input multi-output antenna design for THz applications

This paper presents a compact graphene-based multi-input multi-output (MIMO) antenna for wireless communications operating in frequency band (0.1-10) THz. This work has been performed with four ports microstrip antennas based on 37×88 μm² a silicon dioxide (Sio₂) substrate and copper on the ground layer, with high isolation by a series of unit cells of graphene selected between adjacent patches to reduce the transmission coefficient and antenna size. Graphene's chemical potential will change by changing the connected DC voltage, leading to bandwidth and resonant frequency variation. The simulation has a reflection coefficient is less than -10 dB at (4.5-10) THz of the frequency scale, mutual coupling (-15 dB), and the gain from (4.7-9) THz is (1.6-6.7254) dB. This paper aims to provide wideband, efficient and reconfigurable with simple graphene-based MIMO antenna for THz applications.