Number Of Graphene Layers Research Articles

Graphene coated 3C-SiC with improved irradiation resistance and enhanced heat conduction property after collision cascade

Graphene/SiC nanocomposites are promising materials with excellent irradiation resistance. In this study, the structure of 3C-SiC coated with graphene layers is proposed to improve SiC's irradiation resistance. The atomistic mechanisms behind the irradiation resistance and irradiation's effect on the thermal conductance of the composite are investigated through molecular dynamics simulations. Results show that the graphene layers effectively enhanced the irradiation resistance of SiC in the composite with increased threshold displacement energy when irradiated with a carbon primary knock-on atom (PKA). Influence factors, i.e., graphene layer number, incident angle of the PKA, and temperature, of irradiation resistance are also studied by collision cascade simulations. In addition, the heat conduction of the composite is enhanced after the irradiation with the 1.5 keV carbon PKA. The resistance dominates the thermal transport at the graphene layers near the interface instead of the interface. The largest temperature drop occurs between the interface and the penultimate graphene layer, consistent with the significant mismatch of their vibrational density of states. After irradiation with the 1.5 keV carbon PKA, the thermal conductance of the graphene/SiC composites increases, and the interface thermal resistance decreases due to the formed bonds between the graphene layers. Overall, this work provides a fundamental understanding of the irradiation resistance and the thermal properties of the graphene/SiC composite.

Lubrication of rough copper with few-layer graphene

It has been demonstrated through experiments and simulations that friction decreases significantly when graphene is used as a solid lubricant on various materials. However, the effect of increasing the number of graphene layers on lubrication is controversial. Some studies predict an increase of friction with the number of layers that can be imputed to increased contact area, others a decrease in friction attributed to increased flexural rigidity of the layers. Herein, atomistic simulations are performed to investigate the atomic mechanisms by which few-layers graphene lubricate rough copper surfaces when probed by a smooth tip. The results of the simulations show that increasing the number of graphene layers drastically reduces friction, while the deformation mechanism is found to change from atomic wear to recoverable flattening of surface steps, as the amount of interlocking between the surfaces is reduced.

Engineering of Chemical Vapor Deposition Graphene Layers: Growth, Characterization, and Properties

AbstractNumerous studies conducted on the layered graphene family—including the monolayer, bilayer, trilayer, few‐layer, and multilayer—draw plenty of attention to stacking modes and twist angles, which are extensively explored for its controlled growth, properties, and applications. This review provides a comprehensive overview of current challenges and opportunities for the chemical vapor deposition (CVD) growth, characterization, and electrical properties of graphene depending on the layer number and twist angles. Various state‐of‐the‐art innovations using the CVD method, which incorporates graphene synthesis through the control of metal substrates, layer numbers, and twist angles, are presented. The underlying growth mechanisms are discussed in terms of the interactions among graphene substrates/layers and its dynamic process. The characterization methods for determining the layer number and twist angle of graphene layers are summarized. Furthermore, the electrical properties and applications of graphene, particularly magic‐angle twist bilayer graphene, are briefly introduced. Finally, outlooks and perspectives for the engineering of CVD graphene layers are discussed.

Design and modelling of reconfigurable surface plasmon resonance refractive index sensor employing graphene and Sb2S3 for detection of dengue virus

This research addresses the design and analysis of a highly sensitive reconfigurable surface plasmon resonance (SPR) sensor for the detection of dengue virus. The SPR sensor is designed with successive layers of SF11 prism, Ag, graphene, antimony trisulphide (Sb2S3), and sensing medium. The sensing medium is infiltrated with various normal and dengue infected blood components like plasma, platelets, and hemoglobin. The angular reflectivity is investigated by employing the well-established transfer matrix method. Geometrical parameters like thickness of the Ag layer and number of graphene layer are sensibly optimized to attain high performance. The proposed structure is modelled in COMSOL Multiphysics environment to investigate the electric field intensity near the Sb2S3 and sensing medium interface. It is perceived that by switching the phase of Sb2S3 from amorphous to crystalline, the sensitivity is increased from 124.61°/RIU to 180.76°/RIU, 96.66°/RIU to 225.75°/RIU, and 127.42°/RIU to 216.57°/RIU for plasma, platelet and hemoglobin cell respectively.

Refractive index (RI) sensing by a D-shaped photonic crystal fiber with a deposited graphene–polymethyl methacrylate (PMMA) platform

A D-shaped photonic crystal fiber (PCF) with graphene-polymethyl methacrylate (PMMA) stack was employed to determine the refractive index from 1.33 to 1.41 and improve the extinction ratio. The proposed sensor was numerically analyzed using the finite element method. The polishing depth, period of the graphene-PMMA stack, and number of graphene layers on the sensing performance of the proposed structure were evaluated. The results indicate that the spectrum and sensitivity may be modulated. The proposed sensor exhibits a wavelength sensitivity of 2200 nm/RIU, a wavelength resolution of 4.54 × 10−5 RIU, and linearity of 0.9918 with a high extinction ratio. Thus, this device has potential applications in PCF sensors.

Enhancing the photo-response characteristics of graphene/n-Si based Schottky barrier photodiodes by increasing the number of graphene layers

The impact of the number of graphene layers on the spectral responsivity and response speed of graphene/n-type Si (Gr/n-Si)-based Schottky barrier photodiodes is investigated. Gr/n-Si photodiode devices are fabricated by transferring chemical vapor deposition-grown graphene layers one by one on n-Si substrates, reaching up to three graphene layers. The devices show a clear rectifying Schottky character and have a maximum responsivity at a peak wavelength of 905 nm. Wavelength-resolved and time-dependent photocurrent measurements demonstrated that both spectral responsivity and response speed are enhanced as the number of graphene layers is increased from 1 to 3 on n-Si substrates. For example, the spectral responsivity and the response speed of the fabricated device were found to be improved by about 15% (e.g., from 0.65 to 0.75 AW−1) and 50% (e.g., 14 to 7 μs), respectively, when three graphene layers are used as the hole-collecting cathode electrode. The experimentally obtained results showed that the device parameters, such as spectral responsivity and response speed of Gr/n-Si Schottky barrier photodiodes, can be boosted simply by increasing the number of graphene layers on n-Si substrates.

Structure–property relations of three-dimensional nanoporous template-based graphene foams

Recently, much attention has been directed to 3D graphene structures due to their potential of retaining intrinsic 2D graphene properties, in combination with structural flexibility and tunable porosity. From a theoretical point of view, however, it is challenging to build 3D graphene foam structures that accurately represent experimental topological configurations. Here, we generate open-cell 3D graphene structures that closely reflect template-based manufacturing techniques and investigate their mechanical properties. We use all-atom molecular dynamics simulations to relate the overall stiffness, collapse stress and fracture properties to the underlying graphene microstructure represented by the graphene relative density, template relative density and number of graphene layers. We do so for four different template morphologies: gyroids, regular foam (BCC), random foam and nanoporous gold. The overall mechanical properties as a function of graphene relative density are analyzed in terms of power law relations to probe the microstructural deformation modes. Our results show that the open-cell 3D graphene structures feature bending as the dominant deformation mode, with regular graphene foams having the highest stiffness and strength and random foams the lowest. For gyroids we found that a higher template relative density leads to reduced mechanical properties but improved ductility. A similar trend was observed when the number of graphene layers was increased: enhanced ductility but at the expense of a reduced strength. Interestingly, we found that for low graphene density, the gyroids feature a strong self-stiffening response, leading to improvements in both strength as well as ductility. Our findings can be used as a guideline for the experimental design of innovate and lightweight graphene structures with strongly enhanced mechanical properties.

Thickness-dependent neutralization of low-energy alkali-metal ions scattering on graphene

A challenging effort is under way to understand the essence of the quantum size effect of two-dimensional materials in order to achieve the ultimate goal of arbitrarily tailoring their properties in the near future. Here we present experimental and theoretical study of resonant neutralization of low-energy alkali-metal ions on clean and graphene-covered polycrystalline copper surfaces. The ion neutralization strongly depends on the number of graphene layers, and it gradually saturates for three to five layers of graphene. This result is consistent with that for the graphite surface. The neutral fraction for the clean polycrystalline copper surface is found to be significantly higher than that for the graphene-covered surface, which is not consistent with known regularities. We quantitatively explain those observations through the small energy level width of resonant electron transfer that is determined by the special electronic structure of graphene layers. This finding indicates that resonant neutralization spectroscopy has promising applications in the detection of the quantum size effects of two-dimensional materials at an atomic layer level.

A First-Principles Study on the Multilayer Graphene Nanosheets Anode Performance for Boron-Ion Battery.

Advanced battery materials are urgently desirable to meet the rapidly growing demand for portable electronics and power. The development of a high-energy-density anode is essential for the practical application of B3+ batteries as an alternative to Li-ion batteries. Herein, we have investigated the performance of B3+ on monolayer (MG), bilayer (BG), trilayer (TG), and tetralayer (TTG) graphene sheets using first-principles calculations. The findings reveal significant stabilization of the HOMO and the LUMO frontier orbitals of the graphene sheets upon adsorption of B3+ by shifting the energies from −5.085 and −2.242 eV in MG to −20.08 and −19.84 eV in 2B3+@TTG. Similarly, increasing the layers to tetralayer graphitic carbon B3+@TTG_asym and B3+@TTG_sym produced the most favorable and deeper van der Waals interactions. The cell voltages obtained were considerably enhanced, and B3+/B@TTG showed the highest cell voltage of 16.5 V. Our results suggest a novel avenue to engineer graphene anode performance by increasing the number of graphene layers.

Characterization of CVD-synthesized graphene films transferred on different substrates using the scanning probe microscopy electrical techniques

The use of local electrical characteristics of graphene films prepared by chemical vapor deposition (CVD) method on Cu and transferred on different substrates such as glass, SiO 2 /Si and Al 2 O 3 substrates was discussed. The topography, Kelvin probe force microscopy (KPFM), scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM) were compared for graphene on the three different dielectric substrates. The surface potentials of graphene films were investigated using KPFM. It was found that graphene films exhibited nonuniform surface potential distribution depending on the sort of the underlying substrate used, the number of graphene layers and the presence of graphene film defects such as edges, wrinkles etc. The EFM results demonstrated that the local electrostatic properties of graphene film on Al 2 O 3 substrate differ significantly compared to that on glass and SiO 2 /Si substrates. The cross-correlation coefficients between topographical image and SCM- and EFM-images were estimated in order to compare these techniques. It was shown that the techniques can bring complementary information for the characterization of graphene films on different substrates relevant for applications. • The local electrical properties of graphene films were investigated by KPFM, SCM and EFM techniques. • The quantitative values of local dielectric properties are sensitive to the underlying substrate. • Kelvin probe force microscopy. • Scanning capacitance microscopy. • Electrostatic force microscopy.

Nano-projectiles impact on graphene/SiC laminates

The ballistic performance of graphene/silicon carbide laminates under nano-projectile impact is studied using molecular dynamics method, where graphene acts as a barrier coating for its unique intra-layer honeycomb-like structure and interlayer coupling effects. We reveal that under nano-indentation two-layer graphene with AB-stacking on 4H-silicon carbide(0001) exhibits the highest hardness, ∼ 140.06 GPa, comparable to diamond. During impact, the specific total penetration energy of laminates increases with the number of graphene layers n, though the partial of graphene decreases as n ≤ 3, which results from the van der Waals coupling effect of graphene on silicon carbide substrate. The ballistic limit velocity of silicon carbide coated by five-layer graphene is 69.4% higher than that of bare silicon carbide, leading to an increase of specific total penetration energy, ∼ 43.3%. It is interesting that the ballistic performance of two-layer graphene/silicon carbide is enhanced by the formed sp3 bonds and residual bending deformation under secondary impact (after the first low-velocity impact treatment), with the ballistic limit velocity and specific total penetration energy increased by 6.5% and 14.3%, respectively. Graphene is a promising coating that can preserve the functional integrity of materials underneath against hypervelocity impact.

Direct synthesis of graphene on silicon by reactive magnetron sputtering deposition

In the present research, the graphene was grown directly on the Si (100) substrate by a high-power impulse reactive magnetron sputtering the copper target. The samples' structure, morphology, and composition were investigated by Raman scattering spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy. The synthesis temperature, time, sample position in relation to the magnetron, and grid bias effects were studied. The graphene layer number decreased with growth temperature and distance between the sample and magnetron. The defects density in graphene decreased, and graphene crystallite size increased with synthesis temperature. These parameters were changed with lateral movement of the sample's position. The graphene layer number and defects density non-monotonically depended on the grid bias voltage. We revealed that the synthesis time, the distance between the substrate and the magnetron cathode target surface, and the grid bias voltage determine the graphene surface morphology and the shape and size of the graphene flakes. It was explained by competition between the graphene growth from the CHx species, growth activation by hydrogen, etching by hydrogen and argon ions, radiative defects creation, hydrogen atoms adsorption. The changes of the electrons, argon ions and copper atoms concentration and energy, and methane dissociation products density were taken into account. The temperature gradient and ion bombardment induced stress and their release were considered.

The Theoretical Study of Kink Deformation in Graphite Based on Differential Geometric Method.

Kink deformation is often observed in materials with laminated layers. Graphite composed of stacked graphene layers has the unique laminated structure of carbon nanomaterials. In this study, we performed the interlayer deformation of graphite under compression using a simulation of molecular dynamics and proposed a differential geometrical method to evaluate the kink deformation. We employed “mean curvature” for the representativeness of the geometrical properties to explore the mechanism of kink deformation and the mechanical behaviors of graphite in nanoscale. The effect of the number of graphene layers and the lattice chirality of each graphene layer on kink deformation and stress–strain diagrams of compressed graphite are discussed in detail. The results showed that kink deformation occurred in compressed graphite when the strain was approximately equal to 0.02, and the potential energy of the compressed graphite proportionately increased with the increasing compressive strain. The proposed differential geometric method can not only be applied to kink deformation in nanoscale graphite, but could also be extended to solving and predicting interlayer deformation that occurs in micro- and macro-scale material structures with laminated layers.

Numerical approach to design the graphene-based multilayered surface plasmon resonance biosensor for the rapid detection of the novel coronavirus

In this article, a graphene-based multilayered surface plasmon resonance (SPR) biosensor of (BK7/WS2/Au/BaTiO3/Graphene) is proposed for the rapid detection of the novel coronavirus (COVID-19). The proposed SPR biosensor is designed based on the angular interrogation attenuated total reflection (ATR) method for rapid detection of the COVID-19 virus. The sensor’s surface plasmon polaritons (SPPs) and the sensing region refractive index (RI) are changed, owing to the interaction of various concentrated ligand-analytes. The specific ligand is mechanized with the proposed sensor surface and the target analyte that has flowed onto the sensing surface. The proposed sensor is capable of detecting the COVID-19 virus rapidly in two different ligand-analytes environments, such as: (i) the virus spike receptor-binding domain (RBD) as an analyte and monoclonal antibodies (mAbs) as a probe ligand, and (ii) the monoclonal antibodies (IgG or IgM) as an analyte and the virus spike RBD as a probe ligand. Due to the binding of the target ligand-analytes, the concentration level of the sensing region is incremented. As the increment in the concentration level, the RI of the sensing medium increases, therefore the change in RI causes the shift in the SPR angle resulting in the output reflectance intensity. The performance of the multilayered SPR sensor is analyzed numerically using the finite element method (FEM) method. Numerically, the proposed sensor provides the maximum angular shift sensitivity at 230.77 deg/refractive index unit (RIU), detection accuracy (DA) at 0.161 deg−1, and the figure of merits (FOM) is at 37.22 RIU−1. In addition, with each additional graphene layer number (L), the proposed sensor exhibits the angular shift sensitivity increment (1 + 0.7L) times. The novelty of the proposed multilayer (BK7/WS2/Au/BaTiO3/Graphene) sensor is highly angular sensitivity, and capable of detecting the COVID-19 virus rapidly without a false-positive report.

Electrically-modulated infrared absorption of graphene metamaterials via magnetic dipole resonance

To increase the absorption efficiency of graphene-based devices, we propose a metamaterial structure comprising of a square metal plate array on graphene, a dielectric spacer, and a metal substrate. This work numerically demonstrates enhancement of the near-infrared absorption of monolayer graphene via the magnetic dipole resonance in the metamaterial under normal-incidence. Furthermore, the absorption efficiency of graphene-based devices can reach up to 96% with proposed structures incorporating three layers of graphene when the Fermi energy is 0.6 eV. Varying the Fermi energy by varying the applied voltage, is shown to enable an increase of the absorption efficiency of graphene-based devices with a reduction of the Fermi energy. Therefore, the absorption wavelength exhibits a linear electrical modulation in a wide range from 1362 to 1787 nm. The designed graphene light absorber has potential applications in optoelectronic devices such as photodetectors and perfect absorbers. • A new resonance peak appeared by adding single layer graphene. • By increasing the number of graphene layers to three, the absorption efficiency can be increased from 32% to 96%. • By changing the Fermi energy of graphene, the maximum tunable wavelength range can reach 425 nm. • The absorption efficiency of all resonance peaks is more than 87%.

Development and Functionalization of Electrolyte-Gated Graphene Field-Effect Transistor for Biomarker Detection.

In the current study, graphene and its derivatives have been investigated and used for many applications, including electronics, sensing, energy storage, and photocatalysis. Synthesis and fabrication of high quality, good uniformity, and low defects graphene are critical for high-performance and highly sensitive devices. Among many synthesis methods, chemical vapor deposition (CVD), considered a leading approach to manufacture graphene, can control the number of graphene layers and yield high-quality graphene. CVD graphene needs to be transferred from the metal substrates on which it is grown ontoinsulating substrates for practical applications. However, separation and transferring of graphene onto new substrates are challenging for a uniform layer without damaging or affecting graphene's structures and properties. Additionally, electrolyte-gated graphene field-effect transistor (EGGFET) has been demonstrated for its wide applications in various biomolecular detections because of its high sensitivity and standard device configuration. In this article, poly (methyl methacrylate) (PMMA)-assisted graphene transferring approach, fabrication of graphene field-effect transistor (GFET), and biomarker immunoglobulin G (IgG) detection are demonstrated. Raman spectroscopy and atomic force microscopy were applied to characterize the transferred graphene. The method is shown to be a practical approach for transferring clean and residue-free graphene while preserving the underlying graphene lattice onto an insulating substrate for electronics or biosensing applications.

Photo Effect Studies in Graphene/N-GaAs Schottky Junction Using NEGF Method for Photovoltaic Application

In this paper, we present the photovoltaic characteristics of nanoscale Schottky junction solar cell consisting of graphene and GaAs using numerical simulation based on non-equilibrium Green’s function formalism. In our model, light-matter interaction is formulated by the coupling and scattering self-energy matrices whereas heterostructure is designed with a Hamiltonian matrix. An efficiency of 2.36% is obtained for monolayer graphene on GaAs; the efficiency is later enhanced to 5.40% by increasing both the number of graphene layers and the doping concentration of GaAs. The parameters to calculate power conversion efficiency, series and shunt resistances are extracted from the J-V characteristic. The I-V characteristic is also numerically simulated to extract reverse saturation current, ideality factor, and rectification ratio. Moreover, the power density is calculated for the optimized structure; the maximum power density of 7.46 mW/cm2 is obtained for four layers of graphene and a doping concentration of 1017/cm3 in GaAs.

Wetting Stability of Supported Graphene in Ambient Environment

The evaluation of the wetting stability of supported graphene in ambient environment is important for its practical applications. Herein, it is shown by experiments that a monolayer graphene coating can alter the water contact angles of various substrates to a converged value around 80–85° in ambient environment, almost independent of substrate materials, graphene layer numbers as well as long‐term air exposure up to 14 months. First‐principles calculations and van der Waals modeling indicate that a monolayer graphene is sufficient to alter both short‐range and long‐range interactions of a water molecule with various substrates to a converged state. The stable wettability of graphene would facilitate its practical applications, ranging from functional coatings, liquid gated electronic devices, and other areas requiring its exposure to water.

Graphene-Based Opto-Thermoelectric Tweezers.

Since the discovery of graphene, its excellent physical properties have greatly improved the performance of optoelectronic devices and brought important technological advances to optical research and its applications. Here, graphene is introduced to the field of optical-tweezer technology and demonstrate a new graphene-based opto-thermoelectric tweezer. This technology not only reduces the incident light energy required by two orders of magnitude (compared with traditional optical tweezers), it also brings new advantages such as a much broader working bandwidth and a larger working area compared to those of widely researched gold-film-based opto-thermoelectric tweezers. Compared with gold film, graphene exhibits higher thermal conductivity and higher uniformity and is easier to process. Thus, it is found that even monolayer graphene provides stable trapping for particles in a broad bandwidth and that performance is enhanced as the number of graphene layers increases. Furthermore, parallel trap multiple particles as desired shapes can be easily generated with structured graphene patterns. This work demonstrates the enormous application potential of graphene in optical-tweezer technology and will promote their application to the trapping or concentration of cells and biomolecules as well as to microfluidics and biosensors.

Analysis of hybrid plasmon-phonon-polariton modes in hBN/graphene/hBN stacks for mid-infrared waveguiding.

Guiding mid-infrared (mid-IR) signals provide wide-ranging applications including chemical sensing, thermal imaging, and optical waveguiding. To manipulate mid-IR signals on photonic chips, it is critical to build a waveguide that provides both sub-diffraction field confinement and low loss. We present a mid-IR waveguide made up of a multilayer graphene/hexagonal boron nitride (hBN) stacking (MLGhS) and a high-refractive index nanowire. The guided mode of the proposed waveguide structure is formed by coupling the fundamental volume plasmon polariton with the fundamental hyperbolic phonon polariton in hBN, and is then modulated by a high-index nanowire. Interestingly, we found that the effective index, propagation length, and mode area of the guided mode vary as the dependences of N-1, N, and N3/2, where N is the number of graphene layers. In addition, an anomalous result, which reveals Lp and Am monotonously decrease as Fermi energy increases that is not observed in conventional graphene plasmon waveguides, occurs in the present structure. The modal properties are analyzed by altering geometry effects and material parameters, and by crossing the upper Reststrahlen band of hBN from the wavevector k = 1,300 to 1,500 cm-1. Furthermore, crosstalk between adjacent waveguides are investigated to assess the degree of integration. The proposed idea not only provides a potential approach for designing tunable and large-area photonic integrated circuits, but it also has the potential to be extended to other 2D materials such as silicone, germanene, and stanene.