A Highly Sensitive Dual-Core Photonic Crystal Fiber Based on a Surface Plasmon Resonance Biosensor with Silver-Graphene Layer

A highly sensitive dual-core photonic crystal fiber based on a surface plasmon resonance (PCF-SPR) biosensor with a silver-graphene layer is described. The silver layer with a graphene coating not only prevents oxidation of the silver layer but also can improve the silver sensing performance due to the large surface-to-volume ratio of graphene. The dual-core PCF-SPR biosensor is numerically analyzed by the finite-element method (FEM). An average spectral sensitivity of 4350 nm/refractive index unit (RIU) in the sensing range between 1.39 and 1.42 and maximum spectral sensitivity of 10,000 nm/RIU in the sensing range between 1.43 and 1.46 are obtained, corresponding to a high resolution of 1 × 10⁻⁶ RIU as a biosensor. Our analysis shows that the optical spectra of the PCF-SPR biosensor can be optimized by varying the structural parameters of the structure, suggesting promising applications in biological and biochemical detection.

     

Actively Tunable Fano Resonance Based on a T-Shaped Graphene Nanodimer

We present the strength modulation and frequency tuning of Fano resonance by employing a graphene nanodimer formed by two coplanar perpendicular nanostrips with different dimensions. The Fano resonance is induced by destructive interference between the bright dipole mode of a short nanostrip and the dark quadrupole mode of a long nanostrip. The strength, line width, and resonance frequency of the Fano resonance can be actively modulated by changing the spatial separation of those two graphene nanostrips and the Fermi energy of the graphene nanodimer, respectively, without re-fabricating the nanostructures. The tuning of the strength and resonance frequency can be attributed to the coupling strength and optical properties of graphene, respectively. Importantly, a figure of merit value as high as 39 is achieved in the proposed nanostructures. Our results may provide potential applications in optical switching and bio-chemical sensing.     

Controlling Optical Absorption of Graphene in Near-infrared Region by Surface Plasmons

Nowadays, graphene has many applications in optical instruments, biosensors, gas sensors, photovoltaic cells, and so on. In this study, we aimed at investigating the optical properties of graphene under the influence of plasmons created in one-dimensional photonic crystal structure by making use of the absorption spectrum. We put the gold photonic crystal in adjacent to graphene and placed an antireflection layer on top of it. Then, we studied the behavior of graphene absorption peaks in a near-infrared region. By analyzing the graphene behavior in this region, we observed that graphene absorption was increased up to 40% and graphene absorption value in absorption peak, absorption peak wavelength, absorption spectra width, and also its absorption spectra in a wide wavelength range from 1000 to 2500 nm, could be controlled by making use of different factors such as the substance of antireflection layer and photonic crystal geometric dimensions. This structure can make many applications possible for graphene such as using it to build biosensors to identify uric acid and some of the lipids that have specific significances in detecting atherosclerotic lesions as well as diagnosing the states of disease.     

Optical Near-Field Enhancement with Graphene Bowtie Antennas

In this paper, the optical near-field enhancement of graphene bowtie antennas is numerically investigated at terahertz frequencies using boundary element method. The enhanced field intensity at the gap region is a result of the mutual coupling between two triangular elements upon the excitation of graphene plasmons. Firstly, wide plasmon frequency tunability is demonstrated by changing the chemical potential of graphene without the need to alter the antenna geometry. Secondly, by varying the tip angle and radius of curvature of the graphene antennas, the field intensity enhancement at the gap center of the two-element antennas is systematically studied. It is found that graphene bowtie antennas with two round-cornered equilateral triangles have superior performance to other two-element antennas, such as ribbon pair, sharp-cornered bowtie, and disk pair antennas. Last but not least, by applying a moderate chemical potential of 0.4 eV to graphene bowtie antennas, we found that the field intensity enhancement at gap center is about 220 times as much as using gold of comparable sizes. In short, graphene bowtie antennas of rounded corners give rise to considerable near-field enhancement and are promising for a wide range of applications such as molecular sensing at terahertz frequencies.

     

Tunable Plasmon-Induced Transparency of Double Continuous Metal Films Sandwiched with a Plasmonic Array

Making a continuous metal film with near-unity transparency has received more and more attention in recent years because of its potential applications for various optoelectronic devices. Here, we theoretically show that a high tunable plasmon-induced transparency metal film structure can be performed by double continuous metal films inserted with a two-dimensional hexagonal lattice array of plasmonic nanopariticles. The proposed structure shows near-unity anti-reflection and intensively enhanced transmission via the cooperative effects of strong resonant near-field light input and output coupling by the plasmonic array and the excitation of surface electromagnetic waves of the metal films. The optical response can be efficiently mediated by varying the sizes of nanoparticles and the separated distance between the metal array and the metal films. With the merits of high transparency, sub-wavelength sizes and wholly retained metal characteristics including high conductivity via using the pure metallic materials, the structure proposed here suggests various potential applications in optoelectronic integrated circuits.     

Surface Plasmon Polariton Waveguide by Bottom and Top of Graphene

Semiconductor surface plasmon polariton (SPP) waveguide has unique optical properties and compatibility with existing integrated circuit manufacturing technology; thus, SPP devices of semiconductor materials have wide application potential. In this study, a new integrated graphene SPP waveguide is designed using the bottom and top roles of graphene. Moreover, a T waveguide structure is designed by InGaAs of semiconductor gain, with rectangular GaAs material on both sides. The structure adopts light to stimulate the SPP, where its local area is enhanced by the interaction between two interface layers and a semiconductor gain and where its frequency can be adjusted by the thickness of the graphene. Characteristic analysis reveals the coupling between the T semiconductor gain and the SPP mode. The propagation distance of the waveguide can reach 75 cm, the effective mode field is approximately 0.0951λ ², the minimum of gain threshold is approximately 2992.7 cm^?1, and the quality factor (FOM) can reach 180. The waveguide structure which provides stronger localization can be compatible with several optical and electronic nanoscale components. That means, it can provide light for surface plasmon circuit and also can provide a great development in the low-threshold nanolaser.     

Modulating Plasmonic Sensor with Graphene-Based Silicon Grating

We propose a modulating plasmonic structure device which is composed of a single layer graphene above the silicon Bragg grating with the silica spacer layer. This graphene-based plasmonic modulation provides a broad stop-band with high tunability in the mid-infrared region of the transmission spectra achieved by altering the geometrical parameters of the silicon grating and the gate voltage. By engineering, a phase discontinuity into the graphene-based Bragg grating, we can selectively open a transmission window in the previous stop-band spectra. These proposed graphene-based structures are easy to fabricate and operate, which have potential applications as ultra-compact high-sensitivity sensors.     

High-throughput simulation of the configuration and ionisation potential of nitrogen-doped graphene

The electron emission properties of doped graphene nanoflakes can determine their suitability for a range of technological applications. Here we investigate the impact of varying the location of a substitutional nitrogen dopant on the first and second ionisation potentials of graphene nanoflakes. We use a high-throughput simulation engine in conjunction with the density functional tight binding method to calculate the properties of both armchair and zig-zag structure nanoflakes containing 1014 carbon atoms. Our results show that dopant location does affect the ionisation potentials, particularly for the armchair structure, and that there is a natural separation into interior and peripheral regions. A simple statistical analysis indicates that the resolution of electronic emissions can be maximised by restricting the nitrogen dopant to the interior region of the armchair nanoflake.     

Tunable Plasmonic Dispersion and Strong Coupling in Graphene Ribbon and Double Layer Sheets Structure

Based on the interplay between propagating surface plasmon polaritons (PSPs) in graphene ribbon and double layer sheets structure, we theoretically demonstrate a tunable strong coupling mechanism significantly different from reported conventional noble metal nanostructures. The strong electromagnetic coupling between the low order antisymmetric and high order symmetric PSPs modes occurs due to the intersections of dispersion curves, which leads to a modification of plasmonic dispersion and multiple significant anti-crossing regions. Of particular, this strong coupling is controllable through external gate voltage of graphene sheets or ribbon. The results offer an effective regime to dynamically tune the interaction of graphene PSPs, which may find applications in the field of nanophotonic devices in the mid-infrared range.     

Narrowband Light Total Antireflection and Absorption in Metal Film–Array Structures by Plasmonic Near-Field Coupling

We study the cooperative effects between plasmon gap modes and optical cavity modes of a novel triple-layer structure consisting of double continuous gold films separated by a gold nanosphere array. Narrowband near-perfect antireflection of optical field is achieved for the first time due to the strong near-field light–matter interaction within the deep sub-wavelength gaps between adjacent nanospheres combined with the spatial field confinement effects of the optical cavity built by the double gold films. The coexistence cooperation of near-field dipole plasmon resonances and spatial optical field confinement presents more efficient light modification than that of the individual subsystem and may open a new approach to manage light flow. By varying the period of nanosphere array, the diameter of nanospheres, and the distance between the array and the film, optical behaviors of the proposed structure can be tuned in a wide range. High environmental sensitivity and large figure of merit factor are obtained using this structure as the detecting substrate. Furthermore, ultra-compact structure and high conduction suggest the proposed structure being a good candidate for potential applications in highly integrated optoelectronic devices, such as plasmonic filters and sensors.     

Broad Tunable Nanoantenna Based on Graphene Log-Periodic Toothed Structure

A log-periodic toothed nanoantenna based on graphene is proposed, and its multi-resonance properties with respect to the variations of the chemical potential are investigated. The field enhancement and radar cross-section of the antenna for different chemical potentials are calculated, and the effect of the chemical potential on the resonance frequency is analyzed. In addition, the dependence of the resonance frequency on the substrate is also discussed. It is shown that large modulation of resonance intensity in log-periodic toothed nanoantenna can be achieved via turning the chemical potential of graphene. The tunability of the resonant frequencies of the antenna can be used to broad tuning of spectral features. The property of tunable multi-resonant field enhancement has great prospect in the field of graphene-based broadband nanoantenna, which can be applied in non-linear spectroscopy, optical sensor, and near-field optical microscopy.     

The Tunability of Surface Plasmon Polaritons in Graphene Waveguide Structures

The tunability of propagation properties of surface plasmon polariton (SPP) modes in a waveguide formed by two parallel graphene layers separated by a dielectric layer is studied. For this purpose, the dispersion equation of the structure is numerically solved and the effects of applied bias voltage, the role of effective structural parameters, and electron–phonon scattering rate on the propagation of symmetric and antisymmetric SPP waves are investigated. The results of calculations show that considering the electron–phonon scattering rate as a function of Fermi energy and temperature leads to a considerable decrease in the propagation length of SPPs. As the main result of this work, tuning the propagation characteristics of SPPs is possible by varying any of the parameters such as applied voltage, thickness of insulating layer between two graphene layers and permittivities of dielectric layers, and finally the temperature. It is found that antisymmetric mode benefits from a larger propagation length in comparison with that of the symmetric mode.

     

石墨烯健康风险研究现状及展望

石墨烯是一种新型的二维碳纳米材料,由于具有优异的电子、光学、机械等特性,已经被广泛应用于电子器件、复合材料、能源储存等领域.近年来,石墨烯在生物医药领域崭露头角,其在诸如生物传感器、细胞成像、药物输运、抗菌材料等方面的广泛应用,为生物医药技术带来了突破,也为人体健康带来了福音.然而,随着石墨烯以不同途径进入人们的生活,其对人体及其他生物体的安全构成潜在威胁,引发的健康风险正受到广泛关注.本文从石墨烯对生物体的影响及其同生物体的相互作用方面入手,综述了近年来石墨烯健康风险的研究进展,并且总结归纳了人体抵御石墨烯健康风险的途径及机制,最后指出了未来石墨烯健康风险方面的研究方向.     

Narrow-band enhanced absorption of monolayer graphene at near-infrared (NIR) sandwiched by dual gratings

One possibility of enhancing light absorption in monolayer graphene at near-infrared (NIR) wavelength region with grating structures is proposed and investigated. It is demonstrated that it is possible to achieve near-perfect absorption when a single monolayer graphene is sandwiched between two gratings with optimized geometric parameters at normal incidence for transverse electric (TE) polarization. By means of the rigorous coupled-wave analysis (RCWA), the effects of technological tolerances on the optical response of the structure by varying geometric parameters and incident angle are studied. The proposed photonic structure could be efficiently exploited as a building block for innovative optical absorbers or photodetectors in combination with active materials.     

Slab Thickness Dependence of Localized Surface Plasmon Resonance Behavior in Gold Nanorings

We present detailed experimental and numerical studies of plasmonic properties of gold nanoring (NR) arrays with different slab thicknesses from 15 to 125 nm. The hybrid plasmon resonances for the bonding and antibonding modes in gold NRs exhibit a high slab thickness dependence behavior in optical properties. For the thinner slab thickness below 50 nm, both hybrid modes show large spectral tunabilities by varying the slab thickness. Furthermore, for such hollow NR structure, the enhancements of electric field intensities at the inner and outer ring surfaces when reducing the slab thickness are investigated. We observe a significant transition of field distributions for the antibonding mode. All these features can be understood by surface charge distributions from our simulations. The results of this study offer a potential strategy to design a composite plasmonic nanostructure with large field enhancement for numerous applications.     

Actively Tunable Fano Resonance in H-Like Metal-Graphene Hybrid Nanostructures

Actively tunable Fano resonance has obvious advantages in applications such as chemical or biological sensors, switches, modulators, and optical filters. In this paper, we studied theoretically the actively tunable Fano resonance in H-like metal-graphene hybrid nanostructures at visible and near-infrared wavelengths. We found that the absorption spectrum of H-like metal-graphene hybrid nanostructures has two resonance peaks, and the absorption spectrum has an obvious blue shift compared with that of the H-like metal nanostructures without graphene. The optical properties of different nanostructures are explained by the electric field distribution. Then, the dependence of the Fano resonance on the nanostructure parameters, refractive index of host materials, and graphene Fermi energy is studied. The wavelength and intensity of absorption spectrum can be manipulated by adjusting the structure parameters and host materials. In addition, the wavelength and intensity of absorption spectrum can be manipulated actively by changing the Fermi energy levels of graphene. This study provides a method for designing the actively tunable Fano resonance in H-like metal-graphene hybrid nanostructures.

     

Graphene‐Based Nanocomposites for Energy Storage

Since the first report of using micromechanical cleavage method to produce graphene sheets in 2004, graphene/graphene‐based nanocomposites have attracted wide attention both for fundamental aspects as well as applications in advanced energy storage and conversion systems. In comparison to other materials, graphene‐based nanostructured materials have unique 2D structure, high electronic mobility, exceptional electronic and thermal conductivities, excellent optical transmittance, good mechanical strength, and ultrahigh surface area. Therefore, they are considered as attractive materials for hydrogen (H₂) storage and high‐performance electrochemical energy storage devices, such as supercapacitors, rechargeable lithium (Li)‐ion batteries, Li–sulfur batteries, Li–air batteries, sodium (Na)‐ion batteries, Na–air batteries, zinc (Zn)–air batteries, and vanadium redox flow batteries (VRFB), etc., as they can improve the efficiency, capacity, gravimetric energy/power densities, and cycle life of these energy storage devices. In this article, recent progress reported on the synthesis and fabrication of graphene nanocomposite materials for applications in these aforementioned various energy storage systems is reviewed. Importantly, the prospects and future challenges in both scalable manufacturing and more energy storage‐related applications are discussed.     

Broadband Terahertz Absorption in Graphene-Embedded Photonic Crystals

The absorption in graphene is rather low at terahertz frequencies. Here, we present a graphene-embedded photonic crystal structure to realize broadband terahertz absorption in graphene. The approach provides absorption enhancement in the whole terahertz regime (from 0.1 to 10 THz). It is shown that the average absorption in the graphene-embedded photonic crystal can be enhanced in the multiple propagating bands of the photonic crystals. The absorption efficiency can be further improved by optimizing the characteristic frequency, optical thickness ratio in a unit cell, and the angle of incidence on the photonic crystals. A maximum broadband absorption factor of 28.8% was achieved for fixed alternative dielectric materials. The graphene-embedded photonic crystal is promising for terahertz functional devices with broadband response.     

Design and Simulation of a Novel Tunable Terahertz Biosensor Based on Metamaterials for Simultaneous Monitoring of Blood and Urine Components

In this essay, a tunable metamaterial-based biosensor is proposed for simultaneous monitoring of blood components including cells, plasma, water, thrombus, and urine components as well as glucose, albumin, and urea. The proposed biosensor is based on optical sensors, and it provides real-time, label-free, and direct detection, small size, and cost-effectiveness that can be an alternative tool to other conventional methods. The influence of operating frequency, sample thickness, temperature, and radiation angle on the performance of the sensor is investigated by the finite element method (FEM). Numerical results show that the maximum sensitivity and figure of merit (FoM) in the high frequency are 500 (nm/RIU) and 2000, and for low frequency are 136 (µm/RIU) and 155, respectively. The footprint of the structure is 0.34 µm2, which is remarkably smaller than the other reported biosensing structures. The proposed biosensor has the potential to provide high sensitivity, high FoM, and a wide operating range for biomedical applications.

     

High Sensitivity Nanoplasmonic Sensor Based on Plasmon-Induced Transparency in a Graphene Nanoribbon Waveguide Coupled with Detuned Graphene Square-Nanoring Resonators

A novel nanoscale structure for high sensitivity sensing which consists of a graphene nanoribbon waveguide coupled with detuned graphene square-nanoring resonators (GSNR) based on edge mode is investigated in detail. By altering the Fermi energy level of the graphene, the plasmon-induced transparency (PIT) window from the destructive interference between a radiative square-nanoring resonator and a dark square-nanoring resonator can be easily tailored. The coupled mode theory (CMT) is used to show that the theoretical results agree well with the finite difference time domain (FDTD) simulations. This nanosensor yields a ultrahigh sensitivity of ∼2600 nm/refractive index unit (RIU) and a figure of merit (FOM) of ∼54 in the mid-infrared (MIR) spectrum. The revealed results indicate that the Fermi energy level of the graphene and the coupling distance play important roles in optimizing the sensing properties. Our proposed structure exerts a peculiar fascination on the realization of ultra-compact graphene plasmonic nanosensor in the future.