Graphene-based Structure Research Articles

COULOMB DRAG RESISTIVITY IN DOUBLE-LAYER GRAPHENE: INHOMOGENEITY EFFECTS

We investigate Coulomb drag resistivity in a double-layer system consisting of two parallel monolayer graphene sheets. In calculations, we employ the random-phase approximation to determine the polarizability functions of the graphene layers and the frequency-dependent dielectric function of the structure, taking into account inhomogeneity effects of the background dielectric. Our numerical calculations reveal that Coulomb drag resistivity in double-layer graphene systems steadily increases with increasing temperature but quickly decreases as the interlayer separation increases. The drag resistivity between the two layers in the case of an inhomogeneous background dielectric is substantially larger than that in the case of a homogeneous one. In addition, both the value and the imbalance in carrier density in the layers lead to noticeable changes in Coulomb drag resistivity in the system. Our study results are useful in graphene-based structure applications.

Graphene-based hierarchical structure for significantly enhancing thermal conductivity of composites with high mechanical reinforcement

Significant enhancement in out-of-plane thermal conductivity of carbon fiber/epoxy laminated composites without sacrificing mechanical strength is of great challenge for advanced composites. In this study, a novel graphene-based hierarchical structure was constructed by combining graphene foams (GrFs) with graphene nanoplatelets (GNPs) together and laminating with carbon fiber (CF) fabrics. The GrFs acted as thermally-conductive skeletons in bridging CF fabrics together to remarkably increase out-of-plane thermal conductivity of composites, while the GNPs were helpful to further increasing heat-transfer paths and effectively transferring stress between continuous CFs for high mechanical reinforcement. The hierarchical composites exhibited extremely high out-of-plane thermal conductivity of 2.64 W/m·K, increasing by 158.8 % than that of CF/Ep composites, and they also showed satisfactory tensile, flexural, and interlaminar shear strength. Such high performance is mainly due to the hierarchical structure, continuous heat-transfer paths, synergetic enhancement of GrFs with GNPs, and strong interfacial interactions between components for high-efficiency heat and stress transfer.

Plasmonic induced transparency and slow light integrated device for graphene-based metamaterial

The terahertz excitation characteristics of a graphene-based band structure are studied. This structure has different planar band structures that can excite two bright modes and then it can achieve an excellent plasmonic induced transparency effect through the two bright modes. By analyzing the boundary conditions of the electromagnetic field, the dispersion relationship of this structure can be smoothly obtained. Furthermore, the internal loss factor in the matching coupled mode theory can be calculated. Meanwhile, the tuning performance of this simple structure is analyzed through the external voltage. The Fermi level regulated by voltage is also analyzed, and its influence on the entire tuning mechanism is studied. A detailed analysis is conducted on the slow light performance of this structure, and the influence of Fermi level on the slow light performance is explored. This investigation is expected to provide potential theoretical foundations for slow light, optical storage, and other fields.

Graphene-based polarization insensitive structure of ultra-wideband terahertz wave absorber

Graphene, a new smart material, has gained a lot of attention recently because of its tunable band structure and strong light-matter interaction. In comparison with typical absorbers, graphene absorbers have emerged as a highly attractive substitute for various types of applications. To broaden the absorption bandwidth, a two-dimensional graphene-based ultra-wideband and polarization-insensitive novel terahertz (THz) absorber with absorption over 95 % from 3.0 THz to 8.5 THz is proposed, with peak absorption of 99.9 % at 6.6 THz and average absorption of 98.4 % for the 5.5 THz bandwidth. The surface plasmon increased by the gold-graphene structure, the Mei resonance, and the interference cancellation between metasurfaces collectively contribute to the ultra-wideband absorption. To obtain nearly perfect broadband terahertz absorption, a single layer of graphene is used. The finite difference time domain (FDTD) approach is used for absorber analysis. In addition, the absorber is insensitive to the polarization angles and incidence angles of incident electromagnetic waves. The proposed graphene-based absorber dominates previously reported wideband THz absorbers in terms of over 95 % bandwidth, absorption peak value, and overall volume. This research will present a novel idea for the design of an ultra-wideband absorber, which can be considered a suitable candidate for different potential applications in terahertz imaging, sensors, photodetectors, and modulators.

Tunable triple plasmon-induced transparency in E-type graphene metamaterials.

Enhancing light-matter interaction is crucial for boosting the performance of nanophotonic devices, which can be achieved via plasmon-induced transparency (PIT). This study introduces what we believe to be a novel E-type metamaterial structure crafted from a single graphene layer. The structure, comprising a longitudinal graphene ribbon and three horizontal graphene strips, leverages destructive interference at terahertz frequencies to manifest triple plasmon-induced transparency (triple-PIT). Through a comparison of simulations using the finite difference time domain (FDTD) method and theoretical coupled-mode calculations, we elucidate the physical mechanism behind triple-PIT. Our analysis shows that the PIT effect arises from the interplay between two single-PITs phenomena, further explored through field distribution studies. Additionally, we investigate the impact of varying Fermi levels and carrier mobility on the transmission spectrum, achieving amplitude modulation in photoelectric switches of 85.5%, 99.2%, and 93.8% at a carrier mobility of 2 m2/(V·s). Moreover, we explore the relationship between Fermi levels and carrier mobility concerning the slow light effect, discovering a potential group index of up to 1021 for the structure. These insights underscore the significant potential of this graphene-based metamaterial structure in enhancing optical switches, modulators, and slow light devices.

A Highly Sensitive Plasmonic Graphene-Based Structure for Deoxyribonucleic Acid Detection

In this study, a Kretschmann structure with a hybrid layer of graphene–WS2 is designed to develop a sensitive biosensor for deoxyribonucleic acid detection. The biosensor incorporates a 45 nm gold layer as the active layer and a thin film of chrome as the adhesive layer. Through the optimization of the graphene and WS2 layers, combined with the implementation of a silicon layer, we can enhance the nano-sensor’s sensitivity. The thin silicon layer acts as a protective barrier for the metal, while also increasing the volume of interaction. Consequently, by adjusting the thickness of the active metal and adding a silicon layer, we achieve higher sensitivity and a lower full width at half maximum, leading to sensitivity of 333.33°/RIU. The designed structure is analyzed using numerical techniques and the finite difference time domain method, allowing us to obtain the optical characteristics of the surface plasmon polariton sensor. Various parameters are calculated and evaluated to determine the optimal conditions for the sensor. Furthermore, the total size of the sensor is 2.228 µm2.

An Ultramicroporous Graphene-Based 3D Structure Derived from Cellulose-Based Biomass for High-Performance CO2 Capture.

The use of powered activated carbon is often limited by inconsistent particle sizes and porosities, leading to reduced adsorption efficiencies. In this study, we demonstrated a practical and environmentally friendly method for creating a 3D graphene nanostructure with highly uniform ultramicropores from wood-based biomass through a series of delignification, carbonization, and activation processes. In addition, we evaluated the capture characteristics of this structure for CO2, CH4, and N2 gases as well as its selectivity for binary-mixture gases. Based on textural and chemical analyses, the delignified monolith had a lamellar structure interconnected by cellulose-based fibers. Interestingly, applying the KOH vapor activation technique solely to the delignified samples led to the formation of a monolithic 3D network composed of interconnected graphene sheets with a high degree of crystallinity. Especially, the Act. 1000 sample exhibited a specific surface area of 1480 m2/g and a considerable pore volume of 0.581 cm3/g, featuring consistently uniform ultramicropores over 90% in the range of 3.5-11 Å. The monolithic graphene-based samples, predominantly composed of ultramicropores, demonstrated a notably heightened capture capacity of 6.934 mol/kg at 110 kPa for CO2, along with favorable selectivity within binary gas mixtures (CO2/N2, CO2/CH4, and CO2/CH4). Our findings suggest that this biomass-derived 3D structure has the potential to serve as a monolithic adsorbent in gas separation applications.

Bi-functional dynamic tunable absorber and highly robust polarisation converter for graphene-based metasurface

In this study, a graphene-based metasurface structure with bi-functional dynamically tunable absorber and highly robust polarisation converter is proposed. The device primarily consists of two functional tiers. The top tier of cyclically patterned graphene and the back of a fully reflective gold mirror, which are separated by an intermediate tier of SiO2 dielectric to form a typical sandwich structure. The proposed device is numerically calculated by finite element method (FEM), and the equivalent R-L-C circuit model is built to validate the calculated results. The proposed reflective-type circularly to circularly polarisation converter (RCCPC) has a wide operating band of 0.8 THz (2.12 THz to 2.92 THz) and can obtain near unity polarisation conversion rate (χPCR). It is worth noting that the device is also immune to structural parameter deviations. In addition, due to the excited charge of monolayer graphene has the cyclotron property in a static magnetic field, the cross-polarised component of the polarisation converter can be increased by applying a vertical magnetic field, which provides a feasible method to improve the energy conversion rate of the device. At the same time, the device can also serve as a narrowband dual channel absorber, with 95 % absorption effect. In addition, the tunability of graphene is based on the correlation between conductivity and Fermi energy. As the Fermi energy changes, the working frequency of the device is shifted, realizing the dynamic tunable absorber and polarisation converter. It is believed that these findings provide a way to implement a variety of novel multifunctional photonic device, including polarisation imaging, electromagnetic energy absorption, and integrated photonic devices.

Active manipulation of the plasmonic induced asymmetric photonic spin Hall effect

The asymmetric photonic spin Hall effect (APSHE) induced by surface plasmon polaritons in a graphene-based structure is actively manipulated by external magnetic field and electric field. It is revealed that the spin-dependent splitting exhibits spatio-temporal asymmetric property due to the involvement of the anisotropic graphene. The peak of asymmetry degree in APSHE at the position of reflectance valley corresponds toward a smaller incident angle with the increase of magnetic field intensity or Fermi energy, which is attributed to the tunability of reflectance for the graphene-based structure. Based on the asymmetric splitting shift, a potential application is proposed for detecting low concentration gas molecules and the detection resolution can be dynamically tunable by changing the magnetic field intensity and Fermi energy. This study may provide a new reference in the fabrication of graphene-based plasmonic sensor devices.

Voltage tuning multi-photon processes with a graphene-based Tamm structure

Tamm plasmon modes are used to realize the modulation of multi-photon processes. Through effectively combining the rear-earth doped layer and a monolayer graphene in a Tamm structure, the emission of multi-photon processes can be tuned by the applied voltage. Results show that the proposed structure has a narrow absorption peak near 1550 nm, which is corresponding to the excitation source wavelength of the multi-photon processes. Importantly, the emission intensity of multi-photon processes can be tuned from 1 fold to ∼10.1 fold when we changed the applied voltage. Meanwhile, the emission color of the multi-photon processes can be tuned from yellow to green via adjusting the applied voltage. The proposed voltage tuning approach may be promoted to all kinds of nonlinear optical phenomenons, like Stimulated Raman Scattering, optical mixing and photorefractive effect.

Dual dynamically tunable terahertz graphene-based plasmonic induced transparency and slow light effects

A novel single-layer graphene-based structure is designed in this article. This structure consists of two graphene strips and two graphene blocks. The components of this structure generate two bright modes and one dark mode in the terahertz region, and these three modes undergo destructive interference, leading to the phenomenon of double plasmonic induced transparency. The graphene of this structure has continuity, and the Fermi level can be adjusted by adjusting the bias voltage applied to the structure. Compared with those discontinuous structures, it is easier to achieve tuning function. The structure uses the finite-difference time-domain for data simulation, uses the coupled mode theory for theoretic calculation, and compares the transmission spectra obtained by the two methods. Through observation, it can be found that the frequency positions of the peaks and dips of the simulated transmission spectrum increase with the increase of the Fermi level, showing a perfect linear relationship, which indicates that this structure has great prospects in the modulator. In addition, the structure has achieved good results in the slow light effect, and after measurement, the peak values of group index and group delay can reach up to 380 and 0.241 ps, respectively. By utilizing these advantages, this structure can provide more possibilities for the development and research of slow light fields.

Graphene metasurface based broad band absorber for terahertz sensing applications

In this article, a graphene metamaterial based absorber is proposed for controlling and modulating EM waves at terahertz frequency range. Here, we introduced an absorber that can absorb THz radiation over a wide bandwidth of roughly 2.5 THz. The construction of the proposed absorber contains three different layers. In the proposed construction, a silicon layer is used as a dielectric material that separates the graphene patch from the absorber's bottom golden layer. The bandwidth of the proposed absorber can be improved by varying the chemical potential of the graphene material. Compared with the existing literature, the proposed graphene-based metamaterial structure will find numerous potential applications in THz sensing and detecting applications.

A tunable broadband absorber in the terahertz band based on the proportional structure of a single layer of graphene

This paper presents a novel graphene-based proportional structure for a tunable wideband absorber in the terahertz (THz) frequency range. In order to achieve the ideal design structure, we make the distance between the top graphene structure and the periodic edge remains proportional, enabling excellent absorption with an absorption rate exceeding 90 % within the frequency range of 3.1–6.97 (3.87)THz. Notably, a perfect absorption is achieved at f = 6.5 THz. At f = 4.2 THz, the absorption rate is close to 97 %, and at f = 5.2 THz, the absorption rate is about 91 %. The average absorption rate is 94.6 % in the range of 3.1–6.97 THz. The absorber's impedance is calculated to demonstrate its favorable absorption band. Furthermore, an analysis of the electric field within the absorber reveals the coupling effect of strong electric fields between different regions, leading to the overlapping of absorption peaks and the formation of a wideband response. This allows us to choose regions to combine according to the needs of the application. By adjusting the parameters of the absorber, it exhibits coordinated performance and manufacturing tolerance. Additionally, the absorber shows a certain degree of tolerance to the incident angle of electromagnetic waves. These findings highlight the potential applications of this absorber in optoelectronic devices, THz detection, and stealth technology.

Sandwich-structured graphene composite sponge with multiple cyclic compression for waste liquid treatment under dynamic electrical stimulation response

3D porous graphene nanosponge has broad application prospects in intelligent sensing, wastewater treatment, environmental remediation and other fields. However, the previously reported graphene-based 3D structure sponge column usually has difficulty achieving compression resistance and excellent adsorption effect. In this study, a novel, simple and low-cost sandwich structure is assembled. The carbon fiber/reduced graphene oxide/polydimethylsiloxane (CF/rGO/P) with excellent compression electrical properties is used as the intermediate layer, and the flexible polyvinylidene fluoride/rGO/P (PV/rGO/P) is used as the upper and lower layers. A composite assembled graphene sponge column with outer pressure resistance and middle compression resistance is prepared. Results show that this composite sponge has a small resistance(30–100 Ω/cm). Under 60% compression deformation, the resistance sensitivity could reach 36.44. The physical adsorption of methylene blue (MB) dye has reached more than 93.7% after 24 h, and the electrochemical adsorption rate is 3.12 times faster than the physical adsorption rate. This sandwich assembly structure exhibits an excellent positive synergistic effect, maintaining high adsorption and desorption properties for MB dyes under high compression cycles. It can be applied to the recovery of cationic dyes in the dynamic flow waste liquid, thereby broadening the application of hydrogel graphene nanosponge in the field of environmental protection.

Modelling a near perfect temperature tunable multiband VO2 based photonic-plasmonic absorber within visible and near infrared spectra

This work demonstrates thermal and optical stability with multiple near perfect absorption in a polarizing sensitive one-dimensional vanadium dioxide (VO2) graphene-based nanocomposite plasmonic structure within visible to infrared region (IR). Proposed structure in each phase of VO2 has multiple perfect optical absorption peaks within visible range with a Q-factor near ∼45 which leads the structure to work like an optical switch. An increase in absorption is achieved through plasmonic polaritons of a nearby Ag thin layer directly or through photonic crystal. The temperature turnability of VO2 leads the proposed structure a tunable optical absorber with a hysteresis loop from low to nearly perfect absorbance spectrum. The octonacci quasi periodic proposed structure has highest multiple perfect absorber spectrum comparing other photonic sequences. The peaks of absorption have blue shifted with an increase in volume fraction in both phases. The optical absorption of the structure in metal phase mode alters from wide band to multiple narrow bands with the increment of permittivity of the host composite material within the 1000–1600 nm range. The absorption maximizes in TE mode comparing TM mode due to polarization sensitivity. The structure with optimal thickness and volume mixing ratio in composite has temperature dependency with a thin layer of VO2 has ∼90% absorption. The absorption of the structure can be tuned in both heat and cool mode function of the phase change material (PCM) at an optimum frequency within visible to IR spectrum. These thermal bistable activities may enhance the optical features of the devices.

Optical tunable multifunctional applications based on graphene metasurface in terahertz

Due to the superior properties of graphene and the application potential of surface plasmons, the research of graphene surface plasmons has become a hot research direction. Based on the surface plasmons of graphene, this paper has done some researches on the plasma induced transparency, absorption, and slow light effect. The main work and results of this paper are as follows: we have designed a graphene-based metamaterial structure that can realize a dual plasma induced transparency (PIT) effect. The specific structure is formed by the periodic arrangement of graphene bands (as bright mode) and band edge microchips (as bright mode). We use the finite-difference time-domain (FDTD) method to study the dual PIT effect from the aspect of numerical simulation, and then further study the phenomenon of this device from the theoretical fitting of the coupled mode theory (CMT). The CMT model explores the physical mechanism of dual PIT spectral line and obtains a good fitting result. By studying the formation mechanism of the dual PIT effect, we have found that the graphene band as a bright mode interacts with the band edge microchip as a dark mode, and then the dual PIT is formed by destructive interference of the bright and dark modes. In order to better external modulation, the structure only studies the modulation effect caused by the change of Fermi level affected by the external voltage of graphene. Moreover, we also have studied the slow light performance of this structure, and the slow light coefficient reached 0.236 picoseconds (ps). This proposed coupling system of dual PIT effect has important research significance in optical switches, optical loop, and slow light devices.

Multifunctional graphene-based optoelectronic structure based on a Fabry-Perot cavity enhanced by a metallic nanoantenna.

Optical communications systems are continuously miniaturized to integrate several previously separate optoelectronic devices, organized with silicon-based incorporated circuits, onto a distinct substrate. Modulators and photodetectors have essential roles in photonic systems and operate with different mechanisms. Integrating them into one device is complex and challenging, but these multifunctional devices have numerous advantages. This article uses a graphene/hBN-based structure to modulate, detect, and absorb any signal with the desired frequency in the THz range. The proposed system comprises one unpatterned graphene sheet embedded in bulk hBN with the periodic gold/palladium nanostructure beneath and below it. The perfect absorption, a modulation depth of 100%, and photodetection of more than 20A/W at any desired frequency can be verified.

Band-stop filter based on metal–insulator-metal hybridized with graphene layer in telecommunication regime

Graphene offers unique properties such that changing the incident energy density of the carriers by gate voltage leads to alteration of the chemical potential that can be used in light manipulation of photonic devices. In this work, we propose a band-stop filter hybrid graphene nanostructure composed of a graphene layer which is added to a metal–insulator–metal plasmonic waveguide structure. We use the finite element method to numerically calculate the light transmission of the graphene-based structure for adjusting chemical potential of graphene. Our calculations show that with constant structural parameters the observed transmission is modified when the chemical potential of graphene changes. Also, the transmission can be filtered in specific wavelength by controlling the chemical potential. The result shows the filtering at lower wavelengths by increasing the chemical potential. Moreover, the performance of this structure for the different channel width and refractive index of insulator is studied.

Graphene-coated alumina nano/microfibers as filler for composites

The present work is focused on the preparation and characterization of composite nano/microfibers based on alumina applicable as fillers in ceramic-matrix composites. The graphene-coated Al2O3 microfibers have been prepared in the form of continuous alumina/graphene fibers from electrospun precursors using needle-less electrospinning, calcination, and catalyst-free chemical vapor deposition of graphene layers on the surface of the microfibers. The phase composition and morphology of the composite fibers were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, scanning, and transmission electron microscopy (SEM and TEM). The porosity of the final fibers was evaluated by low-temperature nitrogen adsorption. The surface microstructures of composite fibers were rough and their diameters were in the range from 300 nm to 2 μm. The phase transformation at 1100 °C led to the formation of a mixture of γ-, δ-, and α-Al2O3. TEM results confirmed that the alumina fibers were covered by the 3–4 layers of graphene-based structure. The specific surface area of pure alumina fibers after carbon deposition slightly increased from the initial 40 m2/g to 45 m2/g, due to a slightly wavy surface of graphene layers. Raman spectroscopy and XPS analysis results showed that the surface layer of fibers is formed as graphene oxide. Between the graphene oxide and alumina grains a chemical bonding C–O–Al, C–O–O–Al was discovered as the nucleation of the graphene oxide sheet. The growth mechanism of graphene oxide layers on the surface edges of Al2O3 grains was described.

Polarization-independent multifunction applications based on perfect absorption in a simple graphene metasurface

The perfect absorption is realized in a simple graphene-based metasurface structure in the terahertz range. Tunability of the absorbance spectra in the proposed system is achieved thanks to the adjustable Fermi level of the graphene. The finite difference time domain (FDTD) and coupled model theory (CMT) methods are employed to analyze absorbance spectra. Then, the polarization-independent multifunction applications in the system are discussed. The maximal group index for slow-light effects is 40911, the maximal sensitivity for the sensing is 8886 nm/RIU, and the maximal modulation depth(MD) and the insertion loss(IL) for the on-off modulator are 99.14% and 0.0015 dB, respectively. The results may provide a way to design multifunction micro-nano optical devices.