Number Of Graphene Layers Research Articles

Tuning nanoscale adhesive contact behavior to a near ideal Hertzian state via graphene coverage

We carry out molecular statics (MS) simulations to study the indentation process of Pt (111) surfaces using an indenter with the radius of 5–20 nm. The substrate and indenter surfaces are either bare or graphene-covered. Our simulations show that the influence of the adhesion between the bare substrate and indenter tip can be significantly reduced by decreasing the adhesion strength and adhesion range between the atoms on the substrate and indenter, or by enhancing the substrate stiffness. Our results suggest that the elastic response of the substrate exhibits weaker adhesion after the coating of graphene layers on either side of the contacting interface, which is attributed to the weak interaction between the graphene layers. Based on these principles obtained for the bare substrate, the nanoscale contact behavior of the substrate can be tuned into a near-ideal Hertzian state by increasing the number of graphene layers, applying pre-strains to graphene on substrate, or using large indenters. Therefore, even for strong adhesion between tip, graphene, and substrate, mechanical properties of substrate can be determined by nanoindentation using graphene coverage. Our research provides theoretical guidance for designing adhesion-less coatings for AFM probes and MEMS/NEMS systems.

Performance enhancement of surface plasmon resonance sensor based on Ag-TiO2-MAPbX3-graphene for the detection of glucose in water

In this paper, we presented surface plasmon resonance (SPR) sensors with high performance consisting prism (BK7), silver (Ag), titanium dioxide (TiO2), hybrid organic-inorganic halide perovskites (CH3NH3PbX3 $$\equiv$$ MAPbX3, with CH3=M, NH3=A and X=I, Br) and graphene layers. An SPR sensor based on Ag-TiO2-MAPbI3-graphene and an SPR sensor based on Ag-TiO2-MAPbBr3-graphene. The sensitivity of these sensors is compared with a traditional Ag-TiO2-graphene based SPR sensor. The results show that the proposed sensors have a better sensitivity than the traditional one. Moreover, the thicknesses of Ag, TiO2 and MAPbX3 layers have been optimized to achieve the best performance of the sensors. For SPR sensor based on Ag-TiO2-MAPbI3-graphene, the best performance is obtained where the optimized thicknesses of Ag, TiO2 and MAPbI3 are 60 nm, 5nm and 1.5 nm, respectively. For SPR sensor based on Ag-TiO2-MAPbBr3-graphene, the best performance is obtained where the optimized thicknesses of Ag, TiO2 and MAPbBr3 are 60 nm, 5nm and 2.5 nm, respectively. In addition, the number of graphene layers are investigated and optimized to one layer. Also, compared with existing sensors in the literature, the proposed sensors exhibit higher sensitivity, better detection accuracy and greater quality. Lastly, the sensitivity of the proposed sensor in biomedical application is investigated. Reported sensitivity is 0.0212 deg/gl−1 for sensor based on MAPbI3 and sensor based on MAPbBr3.

Hydrogen-induced marginal growth model for the synthesis of graphene by arc discharge

High-quality graphene is prepared by arc discharge with low cost under hydrogen atmosphere. However, the growth mechanism of graphene synthesis by arc discharge remains unclear. In this paper, the hydrogen-induced marginal growth (HIMG) model is deduced to study the growth mechanism of graphene by combining experiment with numerical simulation results. First, the characteristics of thick edges and thin middle and containing hydrogen are verified by transmission electron microscopy and Raman spectroscopy, respectively. In addition, numerical simulation provides the chemical species and temperature range of graphene growth. Second, the marginal growth pattern of hydrogen transfer and carbon addition is introduced because the C-H and C-C reduce configuration energy and island energy, respectively. Meanwhile, the stacking growth at the margin of the graphene island leads to the longitudinal growth of graphene because of the Van der Waals force and the effect of self-assembly, increasing the number of graphene layers. Finally, graphene sheets with a small amount of hydrogen are deposited on the inner wall after annealing. The investigation of the growth mechanism of graphene under hydrogen atmosphere lays a foundation for the large-scale preparation of graphene by arc discharge.

Absorption characteristics of one-dimensional graphene photonic crystals

In order to study the absorption characteristics of one-dimensional graphene photonic crystals, a TE wave of 300–1000 nm is analyzed theoretically and numerically based on the transfer matrix method. The effects of the incident angle, the structure of the photonic crystal, the number of graphene layers, and the refractive index of the defect layer on the absorption characteristics are analyzed. The results show that the absorption of graphene can be greatly improved by using the micro Fabry–Pérot cavity formed by the defect layer of the photonic crystal. The peak, the position, and the bandwidth of the absorbance can be adjusted by changing the above-mentioned parameters of the photonic crystal. This study provides a way to expand the application of photonic crystals.

A study on the tensile force and shear strain of trilayer graphene

The study of mechanical properties of graphene is one of the hottest topics in graphene physics. As the number of graphene layers increases, the mechanical property changes. Y. Liu et al., J. Mech. Phys. Solids, 60, 591 (2012) [1] have studied the tensile force and shear strain of bilayer graphene. They observed both the parameters increase as the length increases. In this paper, we study the same parameters for trilayer graphene. In trilayer graphene, we observe that with increasing length of the material, the tensile force increases and shear strain decreases. The change of mechanical behaviour from bilayer to trilayer graphene is a transition which would continue to higher number of layers with potential implications in near future.

Mechanical and viscoelastic properties of wrinkled graphene reinforced polymer nanocomposites – Effect of interlayer sliding within graphene sheets

Multilayer graphene sheets (MLGSs) are promising nano-reinforcements that can effectively enhance the mechanical properties of polymer matrices. Despite many studies on MLGSs-reinforced polymer nanocomposites, the effect of wrinkles formed in MLGSs on the reinforcement effect and the viscoelastic properties of polymer nanocomposites has remained largely unknown. In this study, building upon previously developed coarse-grained models of MLGSs and poly(methyl methacrylate) coupled with molecular dynamics simulations, we have systematically investigated nanocomposites with different numbers of graphene layers and various wrinkle configurations. We find that with decreasing degree of waviness and increasing numbers of layers, the elastic modulus of the nanocomposites increases. Interestingly, we observe a sudden stress drop during shear deformation of certain wrinkled MLGSs-reinforced nanocomposites. We further conduct small amplitude oscillatory shear simulations on these nanocomposites and find that the nanocomposites with these specific wrinkle configurations also show peculiarly large loss tangents, indicating an increasing capability of energy dissipation. These behaviors are attributed to the activation of the interlayer sliding among these wrinkled MLGSs, as their interlayer shear strengths are indeed lower than flat MLGSs measured by steered molecular dynamics technique. Our study demonstrates that the viscoelastic properties and deformation mechanisms of polymer nanocomposites can be tuned through MLGS wrinkle engineering.

Effect of Different Rotational Speeds on Graphene-Wrapped SiC Core-Shell Nanoparticles in Wet Milling Medium.

The effects of the wet milling rotating speed on the number of graphene layers and graphene quality, and the conversion efficiency of graphite exfoliate to graphene, were investigated by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The results show that the number of few-layer graphene nanometer sheets (GNSs) (≤10 layers) gradually increases with the increase of rotational speed in the range of 160–240 rpm. The proportion of GNSs with 0–10 layers reaches more than 80% as the rotational speed is increased to 280 rpm. GNS defect types in the composite materials are marginal defects with minimal influence and almost no oxidation. In the range of 160–280 rpm, the intensity of graphite peak decreases and the conversion efficiency of graphene increases with the increase of rotational speed. This is the same as the experimental result obtained by HRTEM.

Modeling of a biosensor using Tamm resonance excited by graphene.

In this paper, nanoscale pores in silicon layers are exploited to model and optimize a one-dimensional hybrid graphene-porous silicon photonic crystal biosensor. The physical nature of the proposed sensor is based on Tamm resonance. The transfer matrix method is applied to detect the change of the index of refraction in an aqueous solution. The proposed model is (PSi1/PSi2)N/G/Substrate, in which PSi1 and PSi2 are porous silicon layers with different porosities, N is the number of periods, and G is the number of graphene layers. The numerical simulations show that the proposed sensor has good performance. The variation of the number of periods, number of graphene layers, porosities, thicknesses of silicon layers, incident angles, and the sample layer thickness affect the performance of the sensor. By varying these parameters, the sensitivity and figure of merit of the sensor can be controlled. The study shows that the sensitivity and figure of merit of the proposed sensor reach 4.75 THz/RIU and 475RIU-1, respectively. The proposed sensor has a good capability in biological detection within terahertz. It is the first time, to our knowledge, that graphene has been used to excite the Tamm resonance using the photonic crystal of porous silicon and using it in biosensing applications.

Manipulation of electronic property of epitaxial graphene on SiC substrate by Pb intercalation

Manipulating the electronic properties of graphene has been a subject of great interest since it can aid material design to extend the applications of graphene to many different areas. In this paper, we systematically investigate the effect of lead (Pb) intercalation on the structural and electronic properties of epitaxial graphene on the SiC(0001) substrate. We show that the band structure of Pb-intercalated few-layer graphene can be effectively tuned through changing intercalation conditions, such as coverage, location of Pb, and the initial number of graphene layers. Lead intercalation at the interface between the buffer layer (BL) and the SiC substrate decouples the BL from the substrate and transforms the BL into a $p$-doped graphene layer. We also show that Pb atoms tend to donate electrons to neighboring layers, leading to an $n$-doping graphene layer and a small gap in the Dirac cone under a sufficiently high Pb coverage. This paper provides useful guidance for manipulating the electronic properties of graphene layers on the SiC substrate.

Characteristics of Refractive-Index Sensor in Graphene-Modified Long-Range Surface Exciton-Polaritons

The organic non-crystalline medium of 5,6-dichloro-2-[[5,6-dichloro-1-ethyl-3-(4-sulfobutyl)-benzimidazol-2-ylidene]-propenyl]-1-ethyl-3-(4-sulfobutyl)-benzimidazolium hydroxide (TDBC) is emerging as possible alternative plasmonic material for noble metal in visible region. In this paper, a novel long-range surface exciton-polariton (LRSEP) sensor based on TDBC film covered with graphene is reported. To enhance the imaging sensitivity, the thickness of TDBC film and the number of graphene layers are optimized. The result shows that the optimized imaging sensitivity is enhanced to 3243 RIU−1 when ns = 1.34. Compared with the traditional noble metal film-based sensor, the proposed LRSEP sensor demonstrates that the imaging sensitivity has been greatly improved. This is the first study of the TDBC film-based LRSEP sensor, which we hope to support the potential development of chemical sensing and bio-sensing.

Investigation of photocatalysis reactions on the single-crystal and polycrystalline graphenes

Graphene has been extensive studied in the field of photocatalysis. Herein, single-crystal and polycrystalline graphenes are prepared by mechanical exfoliation and chemical vapor deposition (CVD), respectively. The photocatalytic properties of polycrystalline graphene are carefully assessed by using 4-nitrobenzenethiol (4-NBT), as a probe molecule, under incident 532 nm laser beam. Similarly, the photocatalytic properties of single-crystal graphene are also investigated with 4-aminothiophenol (PATP) under incident 633 nm laser radiation. In order to solve the problem of uneven distribution of probe molecules on graphene, the internal standard method is adopted by using 2-naphthalenethiol (2-NT), as the internal standard molecule. The experimental findings indicate that PATP can be catalyzed onto the surface of single-crystal graphene under the irradiation of 633 nm laser beam and its catalytic properties significantly increase with decreasing the number of graphene layers. In addition, when single-crystal graphene is used as the Surface-enhanced Raman scattering (SERS) enhancement substrate, the SERS enhancement was also increased with the decrease of the number of layers.

Main structural and mechanical properties of electrospun PAN-based carbon nanofibers as a function of carbonization maximum temperature

In this study, PAN-based carbon nanofibers (CNFs) were synthesized via electrospinning followed by stabilizing and carbonization. The carbonization process was performed by heating the fibrous mats up to a maximum temperature in the region of 800–1600 °C. The effect of carbonization maximal temperature on the structure and tensile strength of carbon nanofiber mats was investigated via SEM, elemental analysis, X-ray diffraction, Raman spectroscopy and tensile testing. Polyacrylonitrile (PAN) concentrations of 6–10% (w/w) and voltages of 14–16 kV were recognized as the optimal electrospinning parameters in order to synthesize of nanofibrous mats without any agglomerated nanoparticles or beads in the mats structure. It is clear from the results that carbon content, crystalline stacking size (Lc), in-plane crystallite size (La) and the number of graphene layers in single crystallite continuously increased with rising carbonization maximum temperature from 800 to 1600 °C, while interlayer d-spacing (d002) decreased at the maximum temperatures of 1000–1400 °C, firstly. This value increased again at the maximum temperatures above1400 °C due to the formation of considerable shrinkages and pores in the CNFs structure. The highest value of tensile strength (206–223 MPa) was recorded for the CNFs mats carbonized up to 1200–1400 °C.

Spin Hall effect of transmitted light for graphene–silica aerogel photonic crystal in terahertz region

Photonic spin Hall effect (SHE) holds great potential applications for the development of spin-based nanophotonic devices. Due to the weak spin–orbit interaction, it is highly desirable to tune and enhance the photonic SHE. However, such a goal remains elusive, especially for the transmitted light. Here, we present the significant enhancement of SHE behavior for transmitted light in terahertz region by introducing the graphene monolayers into adjacent silica aerogel layers of photonic crystal. The spin shift is quite sensitive to the period number and Fermi energy of graphene layers. We find that the value of spin shift is mainly decided by the phase of Fresnel transmission coefficients. In addition, two different tuned regions have been revealed: one is the low frequency region in which the significant feature is the giant spin shift over broad angle and frequency ranges, and the other is the high frequency region where the spin shift can be gradually enhanced as the period number increases. These findings pave the way to achieve the enhanced SHE for transmitted light in terahertz region and may open the possibility for manipulating the photonic SHE.

Vertical Noise Reduction in 3-D Mixed-Signal Integrated Circuits With Graphene Nanoribbon and Carbon Nanotube Interconnects

This study presents the analysis and reduction of vertical crosstalk in mixed-signal 3-D integrated circuits (3-D ICs) with multilayer graphene nanoribbon (MLGNR) and multiwall carbon nanotube (MWCNT) interconnects. The 14-nm technology node is considered for both digital and analog tiers. The assessments are conducted regarding the scattering parameters (S-parameters) for the equivalent circuit model of the transmission lines using the Advanced Design System (ADS) tool. Our studies demonstrate that the MLGNR transmission lines lead to lower mismatch, insertion loss, and vertical crosstalk than their MWCNT counterparts. The results show that using MLGNR improves the area overhead by more than 67% for analog and digital wires. Moreover, our model shows that the vertical noise between the analog and digital tiers is reduced by 1 and 1.62 dB when the intermediate substrate thickness increases from 20 to 30 and 40 μm. The results demonstrate that the perpendicular routing of the MLGNR interconnects reduces the vertical noise by 6.1 dB. Moreover, a 9.21-dB reduction in the vertical coupling is achieved using vertical MLGNRs in the analog IC. Our results also show that using graphene as a shield between the analog and digital chips significantly suppresses the vertical noise between the tiers, and it becomes more effective by increasing the number of graphene layers. According to our results, using one-, two-, and three-layer graphene-shield layers reduces the vertical crosstalk by 10.1, 14.9, and 19.2 dB, respectively. Moreover, the HSPICE simulations demonstrate that the MLGNR interconnects have a lower delay, power, and energy consumption than their MWCNT counterparts in the 3-D mixed-signal architecture.

Mapping graphene layer number at few-micron-scale spatial resolution over large areas using laser scanning

In-line graphene characterization to determine quality, area coverage fraction, and layer number on transparent substrates is critical to large-scale commercial graphene production. Many applications, including biosensors and imbedded diagnostics, flexible electronics, and transparent electrodes, require uniform graphene transfer from its native chemical vapor deposition foil to transparent films. To enable high-volume production of these devices, graphene layer number, quality, and area coverage must be mapped at high spatial resolution to enable growth and transfer process optimization. To this end, we present a spatially resolved optical transmission technique combined with statistical analysis of the measurements to determine graphene layer number on different transparent substrates, including polymer films and glass. This method can be automated and does not require user-inputted threshold values. Our method can effectively map >1 cm2 areas at 10 micron resolution and is not limited by type of substrate or thickness assuming the substrate is transparent. We corroborate these experimental results with simulated data and present guidelines to reasonably assess graphene quality, layer number, and feature size as functions of the experimental parameters.

Wettability of Graphene and Interfacial Water Structure

Understanding the graphene-water interaction, referred to as ‘wettability,’ is important for various applications, such as water desalination, filtration, energy storage, and catalysis. However, most studies on graphene's wettability have been performed with either macroscopic water contact angle measurements or molecular dynamics simulations. The detailed hydrogen-bonding network structure of water molecules at the graphene-water interface has not been fully understood at the molecular level. Here, using vibrational sum frequency generation (VSFG) spectroscopy, we elucidate the interfacial water structure and graphene hydrophobicity at a multilayer graphene-water interface. As the number of graphene layers increases, water molecules with dangling OH group become more populated. We compare the contact angles of water on the multilayer graphene surfaces with VSFG results. An excellent correlation between water adhesion energy of graphene and fraction of dangling OH groups estimated from the water OH stretch VSFG spectrum is established. This observation suggests that the VSFG could be an incisive technique for measuring water's adhesion energy on any spatially confined or blocked surface where the water contact angle cannot be measured. We further anticipate that the VSFG result on the transition from wetting transparency to translucency upon increasing the number of graphene layers will be used to understand the wettability of low-dimensional materials and the role of water structure on electric double layers of graphene-based electrodes.

Thermoelectric and Electrical Properties of Metal Intercalated Bilayer Graphene

1 Introduction There are many heats that are being thrown away around us. About 42% of Japan's exhaust heat is below 200 ℃, and recovery of these low-temperature exhaust heat is hardly progressing. This is because the places where low-temperature exhaust heat is emitted are dispersed in homes, subways, cars, and so on. Inorganic materials such as Bi-Te series that have been used for thermoelectric power generation are rare, expensive, and have no flexibility. Therefore, we focused on graphene, which is a carbon material with a two-dimensional structure. Graphene is a lightweight, flexible material that exhibits unique electrical properties near room temperature. Thermoelectric devices have improved performance by alternately connecting p-type and n-type semiconductor elements. However, since graphene is p-type doped in the atmosphere, there are few reports of stable realization of n-type in graphene.In this study, the thermoelectric properties of high quality graphene synthesized by plasma CVD were evaluated. In addition, we tried to make it n-type by performing metal intercalation on bilayer graphene. 2 Experiments and results 2-1 Synthesis and transfer of graphene Bilayer graphene was synthesized on copper foil by plasma CVD method. Next, the copper foil was etched to transfer graphene to the PET substrate. In addition, graphene with a maximum of 20 layers was prepared by repeating transfer. The graphene of each layer number prepared was evaluated by a Raman spectroscope (HORIBA, XploRA). The laser wavelength used was 532 nm. The number of graphene layers was calculated from the transmittance measured using a haze meter (Nippon Denshoku Industries, NDH5000). 2-2 Evaluation of thermoelectric properties of graphene The Seebeck coefficient and electric conductivity of bilayer and 20-layer graphene were measured with a thermoelectric property evaluation device (ADVANCE RIKO, ZEM-3) (Figure). The Seebeck coefficient was 70 μV / K and the PF was 2.96 mW / mk2 when the sample temperature was 376 K in bilayer graphene. This is a high value compared to the reported organic thermoelectric materials 1). The increase of the number of layers contributed to the improvement of electric conductivity, but did not change the Seebeck coefficient. Further, it was found that the graphene produced was p-type because the Seebeck coefficient had a positive value. 2-3 Elemental intercalation into bilayer graphene An attempt was made to intercalate K for electron doping of graphene. The substrate used was SiO2 / Si, and it was soaked in a 20 mol% KOH solution for 20 minutes immediately before the step of transferring graphene to the substrate 2). Similarly, we tried to intercalate Ca by infiltrating it in a 0.06 mol% Ca(OH)2 solution. The doping states of these samples were evaluated by SEM / EDX. In addition, a field effect transistor using graphene as a channel was manufactured by a lithography process in order to evaluate the electrical characteristics. In the future, the electrical characteristics of graphene will be measured and pn determination will be performed.1) Takao Ishida, Surface Technology, Special Feature: Energy Harvesting, 67, 334-337 (2016)2) T. Yamada, Y. Okigawa, M, Hasegawa, Appl. Phys. Lett. 112, 04310 5 (2018) Figure 1

Structural characterization of graphene nanostructures produced via arc discharge method

Few-layered graphene (FLG) was produced via substrate-free direct current arc discharge between pure graphite electrodes in an originally designed reactor chamber. Previously, parameters influencing the synthesis condition and properties of graphene-like discharge density, precursor composition, electrode diameter/length, reactor design and type and pressure of buffer gases were optimized. In this study, it was observed that carbon structures with different properties deposited in the different regions of the DC arc reactor. The mechanism of graphene formation by the arc discharge method was investigated in terms of the collection side and distance to the arc region. Variations in the distance to arc region result in dissimilar temperature gradients in the reactor chamber, thereby the deposition mechanism of carbon clusters differs with regard to reactor zones. The products collected from the different regions of the reactor were characterized via Raman Spectroscopy and integrated intensity ratio (ID/IG and IG/I2D), full width half at maximum (FWHM), crystallite size (La), defect density (ηD) values were examined. The crystallite size (L002) and average number of graphene layers (N) were determined by X-Ray diffraction (XRD) analyses. In addition, their morphological properties were investigated with scanning electron microscopy (SEM) and transmission electron microscope (TEM). As a result, the carbon nanostructures with high purity and few-layered morphology collected on the anode region of the reactor. While, the purity of few-layered graphene decreased as moving away from the anode region of the chamber. Therefore, it was determined that the properties of graphene were influenced greatly by the temperature distribution and its gradient around the arc plasma.

Tunable far-infrared hyperbolic metamaterial based on graphene-polar dielectric

Abstract In this work, we propose a tunable hyperbolic graphene-polar dielectric metamaterial in the far-infrared range. Here, we employ LiF as a strongly dispersive photonic material which can support surface plasmon polariton within its polaritonic gap. The proposed metamaterial has been analyzed using effective medium approximation (EMA) and transfer matrix method (TMM). It is found that the characterization of the hyperbolic behavior and reflection coefficient of the proposed metamaterial can be effectively controlled by Fermi energy, number of graphene layers and thickness of LiF. According to the results, the hyperbolic bandwidth broadening is possible by increasing Fermi energy, number of graphene layers and decreasing LiF thickness. Furthermore, we have shown fully controllable reflective filtering property of the proposed metamaterial using EMA and TMM. It can be clearly visualized that for thick LiF, effective medium approximation results in complete validation in calculation of the reflection coefficient. This is demonstrating by comparison between the reflection coefficient of the proposed metamaterial calculated using EMA and TMM. We believe that the proposed graphene-polar dielectric metamaterial offers a potential strategy for fine tunning the hybridized surface plasmon phonon polariton in the far-infrared region towards high performance, tunable and active metamaterials.

Photovoltaic performance of non-covalent functionalized single-layer graphene in dye-sensitized solar cells (DSSCs)

In this study, it was aimed to fabricate new effective alternative counter electrodes (CEs) in dye-sensitized solar cells (DSSCs). For this purpose, firstly, single-layer graphene (SLG) thin films were grown by chemical vapor deposition (CVD) method. Then, these films were separately functionalized with 1,8-cineole (ppCin/SLG), D-Limonene (ppLim/SLG) and Thiophene (ppTh/SLG) by plasma polymerization. Number of layers in CVD-grown graphene determined by Raman, transmission electron microscope (TEM) and ultraviolet–visible (UV–Vis) spectroscopy. Chemical structures of plasma polymerised (pp) thin films were investigated by Fourier transform infrared (FTIR) spectroscopy. Photovoltaic parameters of DSSCs were calculated, and electrocatalytic properties of CEs were investigated by electrochemical impedance spectroscopy (EIS). Polymer functionalization greatly enhanced the electrical conductivity and electrocatalytic activity properties of graphene compared to that of SLG. The efficiencies of DSSCs with ppCin/SLG and ppLim/SLG CEs were 1.10% and 1.02%, respectively. As a result, the cell efficiencies of ppCin/SLG and ppLim/SLG could be as alternative materials to platinum (Pt) counter electrode.