Structure Of Graphene Research Articles

Multi-frequency modulator of dual plasma-induced transparency in graphene-based metasurface

Graphene-based metamaterials can generate plasma-induced transparency (PIT), offering a new approach for achieving modulators with optimal modulation performance. This study presents a multi-frequency modulator based on novel monolayer graphene structure. We utilize Coupled Mode Theory (CMT) for thorough theoretical investigations, yielding theoretical values that agree well with simulation results. Moreover, we discuss the implications of the Fermi level on PIT and the influence of graphene carrier mobility on switch modulation. The research findings illustrate the successful realization of a high-performance multi-frequency modulator by indirectly controlling the phase of the dual PIT transmission spectra through an adjustable bias voltage. Notably, at a frequency of 3.93 THz, the increasing of carrier mobility enhances the modulation depth of the modulator from 89.22 % to 97.88 % and reduces the insertion loss from 0.34 dB to 0.12 dB. Hence, our research has substantial implications for designing excellent tunable terahertz optical modulator devices and contributing to the advancement of optical communication systems and optoelectronic applications.

Bandgap formation in graphene doped with BN, TiO2, Al2O3 and ZnO by sintering process

Nanoelectronics emphasises graphene and bandgap opening, where a larger band gap is helpful for different electronic applications. Here, we report on the larger bandgap opening and tuneable bandgap in graphene doped with BN, TiO2, Al2O3 and ZnO by the novel sintering process. In this study, the electronic band structure of graphene is studied systematically in the presence of doping by UV–vis spectroscopy; studies revealed a bandgap formation in graphene. For the first time, a significant and larger bandgap as high as 2.65 eV is observed for graphene-95 % TiO2-3 % BN-2 % combination, and the TiO2 doping and isoelectronic BN opened the π π* band gap of graphene. The quantum confinement effect confined the holes and electrons in the nanoscale semiconductors. As a result, the semiconductor’s band gap increases the energy difference between the empty and filled states. The experimental results are varified by a theoretical approach called machine learning. The current findings open the door to creating graphene-based devices doped with BN, TiO2, Al2O3, and ZnO tailored for band gaps.

Bridging graphene sheets to ultra-high-performance graphene-based bulk materials via Si-C bonding and Y-type carbon structure

Graphene is the strongest material ever identified. However, the fabrication of graphene-based bulk materials from graphene powders presents a significant challenge. Here, a new strategy to fabricate high performance graphene based bulk materials by introducing silicon nanoparticle is proposed. Consequently, ultra-high compressive strength and high flexural strength are achieved, measuring as high as 1102 MPa and 455 MPa, respectively. The compressive strength at the microscale even reaches a remarkable 5.17 GPa. The superior strength of the bulk material is primarily attributed to the Y-type carbon structure and Si-C bonds. The Y-type carbon structures in graphene, produced by the self-propagating high-temperature synthesis (SHS) method, and the Si-C covalent bonds formed at the interface between graphene and SiC contribute to a tight linkage of graphene sheets, thereby preventing slippage of graphene sheets. In addition, the microstructure evolution process of Si-SHS-graphene bulk material is clarified. With the introduction of silicon nanoparticles, the oxidation resistance of graphene based bulk materials is substantially improved, the weight loss is around 6% after oxidized at 1000 °C. This study carries extensive implications for understanding the impact of Y-type carbon structures and the effect of Si-C bonds in graphene-based bulk materials.

The effect of non-metals (O, F) dopant on the electronic structure, Dirac cone, and optical characteristics of graphene sheets applicable for gas sensing

In order to gain a systematic comprehension of the impacts of low-level defects in graphene, ab-initio calculations were performed on monolayer graphene sheets to examine how oxygen and fluorine substitutional impurities affect their energetic stability, electronic and optical characteristics. The optimal configurations, structural stability, electronic band structures, spatial charge density, and optical spectra of graphene single-layer materials doped with oxygen and fluorine atoms are investigated. The fluorine-doped graphene, therefore, showed a lower formation energy than its oxygen-doped counterpart. Additionally, F-doped graphene shows a higher charge density around the fluorine atom than O-doped graphene. Based on band structure analysis, the lower conduction bands of graphene sheets shift below the Fermi state (EF) when two O or F impurities are substituted into it. With two O/F impurity atoms doped into graphene, the conduction states are farther displaced below the EF, resulting in n-type behavior. Consequently, altering graphene structure via an O/F-substituting scheme results from the disruption of the Dirac cone near EF, which has become flat along the high symmetry point (K-point) in the Brillouin zone. Furthermore, the substitution of graphene sheets via O or F impurities exhibit markedly modified optical spectra and refractive indices at low photon energies. As a result, with one or two O/F impurity elements inserted into graphene sheets, the reflectivity and optical conductivity spectra differ at the lowest electromagnetic radiation ranges. Additionally, the electron energy loss functions as well as X-ray absorption spectra of clean and doped graphene monolayers revealed spectral variations at a moderate energy span. These investigations surmise that novel chemical modifications to graphene sheets doped with light non-metallic elements (O/F) may offer the opportunity to tailor their optical characteristics in the infrared spectrum, which may be beneficial in sensor and electrocatalyst uses.

Preparation of phase change functional two-dimensional materials and the tribological properties

The mechanical properties and toughness of phase change materials are often weakened by defects which affect the application of matrix in tribology, and considering the hybridization of nanomaterials is able to increase the upper limit of materials’ performance. In this study, the in-situ polymerization of isopropylacrylamide was used on the surface of graphene and MXene to prepare a phase change two-dimensional composite with reversible phase change under specific temperatures. The composites were dispersed in epoxy resin matrix by KH550 (γ-Aminopropyl triethoxysilane) to realize phase change modulation of tribological properties. The results showed that the tribological properties of the modified epoxy resin coating realized friction reduction and anti-wear functions, and exhibited different tribological properties at different temperatures. The friction coefficient and wear rate of the composite coatings can be reduced to 0.1 % and 82.2 %, respectively, which is mainly attributed to the two-dimensional structure and physical characteristics of graphene and MXene, as well as the mechanical enhancement of the phase change homopolymer and their synergistic effects.

From hydroxyl group to carbonyl group: Tuning the supercapacitive performance of holey graphene

Both hydroxyl group and carbonyl group are the inborn active sites on graphene for energy storage. However, it is difficult to distinguish the definite influence of these functional groups on the supercapacitive performance of graphene due to the considerable changes of total oxygen content (TOC) when adjusting the content of hydroxyl group and carbonyl group on graphene. In this paper, holey graphene was prepared by reoxidation method with ammonium persulfate as oxidant. During the reducing process, four kinds of reductant (formaldehyde, sodium borohydride, vitamin C and glucose) were used to optimize the TOC of graphene. Then, the directional tuning of the content of hydroxyl group and carbonyl group on graphene under a stable TOC was achieved by controlling the addition amount of specific reductant. Results from morphological and electrochemical analysis suggest that high carbonyl content leads to a fluffier graphene structure, bigger specific surface area, higher specific capacitance and lower ion diffusion resistance while high hydroxyl group content results in wider operating potential window and better electrical conductivity. After balancing the content of hydroxyl and carbonyl group in the holey graphene, the assembled supercapacitor owns the high energy density of 22 Wh·Kg−1 and excellent cycling performance (no capacity loss after 10 000 charge-discharge cycles).

Performance enhancement of lithium-ion battery using modified LiMn2O4 cathode followed by ultrasonic-assisted electrochemically synthesized graphene

Herein, the LiMn2O4 (LMO) cathode was modified using ultrasonic-assisted electrochemically synthesized graphene to enhance lithium-ion batteries' charging and discharging performance. Graphene was synthesized from graphite using an electrochemical exfoliation process in which 0.1 M molar (NH4)2SO4 was utilized as the electrolyte with +10 to +12V DC power, followed by ultrasonication in acetone for 2 h. The FESEM, EDX, XRD, Raman, FTIR, UV–vis, and TGA results suggested that ultrasonically treated graphene (EG1) is superior to electrochemically exfoliated graphene (EG2). Thus, EG1 was used to modify the LMO cathode to fabricate lithium-ion batteries. Afterward, the electrochemical performances of the LMO and LMO/EG1 cathode batteries were investigated. Surface morphological analysis revealed that EG1 is composed of two-dimensional, planar, brighter, and less oxidized graphene nanosheets with an average particle size of 18.02 nm. XRD results exhibited that EG1 has a smaller crystalline size and a thinner average stacking thickness of its layered structure than EG2. According to Raman analysis, the intensity ratio I2D/IG of EG2 and EG1 were 0.70 and 0.81, respectively, deduced that both are multi-layered graphene structures; however, EG1 contains a lesser number of graphene layers than EG2. The electrochemical analysis showed that LMO/EG1 cathode batteries have 89 % coulombic efficiency at 0.1C, while LMO batteries have only 81 %. The discharge capacity retention rate of the LMO batteries was 71.4 %, while it was 94.8 % for LMO/EG1 after observing 100 cycles at 0.1 C. Therefore, LMO/EG1 has excellent cycle stability and electrochemical performance and could potentially enhance the performance in hybrid automotive and electronic devices.

Activating doped graphene surface by cobalt-rich sulfide encapsulation toward oxygen reduction electrocatalysis

Similar to proton exchange membrane fuel cell, anion-exchange membrane fuel cell is also a significant energy conversion device for achieving the utilization of clean hydrogen energy. However, the cathodic alkaline oxygen reduction reaction (ORR) is kinetically not favored and usually requires platinum-group metal (PGM) catalysts such as Pt/C to reduce the overpotential. The major challenge in using PGM-free catalysts for ORR is their low efficiency and poor stability, which urgently demands new concepts and strategies to address this issue. Herein, we controllably manufactured a N, S-co doped graphene encapsulating uniform cobalt-rich sulfides (Co8FeS8@NSG) by a universal synthesis strategy. After encapsulation, electron transfer from the encapsulated cobalt-rich sulfides to the doped graphene was greatly promoted, which effectively optimizes the electronic structure of the doped graphene, thereby enhancing the ORR activity of the doped graphene surface. Consequently, the Co8FeS8@NSG exhibits enhanced ORR activity with a higher half-wave potential of 0.868 V (versus reversible hydrogen electrode, vs. RHE) when compared with pure NSG (0.765 V vs. RHE). Density functional theory calculations further confirm that the construction of interface for NSG encapsulating cobalt-rich sulfides could conspicuously elevate the ORR activity through slightly positively-charged C active site and thus simultaneously enhancing electronic conductivity.

Gaussian and Gaussian-pulsed-like Fermi velocity graphene structures

Gaussian and Gaussian-related structures are quite attractive due to its versatility to modulate the electronic transport, including its possibility as electron filters. Here, we show that these non-conventional profiles are not the exception when dealing with Fermi velocity barriers in monolayer graphene. In particular, we show that Gaussian Fermi velocity graphene barriers (G-FVGBs) and Gaussian-pulsed-like Fermi velocity graphene superlattices (GPL-FVGSLs) can serve as electron band-pass filters and oscillating conductance structures. We reach this conclusion by theoretically studying the transmission and transport properties of the mentioned structures. The study is based on the continuum model, the transfer matrix method and the Landauer–Büttiker formalism. We find nearly flat transmission bands or pass bands for G-FVGBs modulable through the system parameters. The pass bands improve as the maximum ratio of Fermi velocities () increases, however its omnidirectional range is reduced. These characteristics result in a decaying conductance (integrated transmission) with . The integrated transmission remains practically unaltered with the size of the system due to the saturation of the electron pass band filtering. In the case of GPL-FVGSLs the GPL profile results in regions of high transmission probability that can merge as flat transmission minibands if the pulse fraction and the superlattice parameters are appropriately tuned. The GPL profile also results in conductance (integrated transmission) oscillations that can be multiplied or reduced in number by adjusting the pulse fraction as well as the superlattice parameters.

Ultra-high temperature microstructural changes of SiC layers in TRISO particles

The SiC layer is the critical layer in the tristructural-isotropic (TRISO) fuel particle with the ability to sustain internal pressure and retain fission products. Further research into the failure mechanisms and tolerance limits of SiC layers at ultra-high temperatures is required. The microstructural evolution of the SiC layer in TRISO particles heat-treated at1800∼2500 °C in argon atmosphere is the focus of this paper. The results show that SiC decomposition and phase transition occur at temperatures above 2200 °C, causing TRISO particles to fail. At 2200 °C, significant decomposition of the SiC layer occurred, resulting in an increase in carbon content on the surface and the appearance of pores. The decomposition reaction of SiC became more complicated at higher temperatures, and the carbon with the graphene structure remained after decomposition. At temperatures above 2300 °C, the SiC phase changed from 3C to 6H, with an abnormal increase in grain size. This study establishes a database for the performance of SiC layers under operation or accident conditions and serves as a reference for future applications of TRISO particles in novel ultra-high temperature reactors.

Effect of hydrogen concentration on the friction evolution mechanism of few-layer graphene: A molecular dynamics study in nanoscratch processes

This article explored the friction evolution mechanism of graphene under different hydrogen concentrations and scratch depths based on molecular dynamics. In a vacuum, graphene exhibits excellent frictional properties when the scratch depth is less than the layer distance of graphene. However, as the depth increases, the diamond tip contacts more CC bonds, and the phenomenon of fracture and recombination of CC bonds in the graphene layer intensifies, increasing surface friction. In a low concentration of hydrogen environment, compared with the friction in a vacuum, it increases due to the interlocking effect of the protruding hydrogen atoms on the diamond tip and the scratch path. As the concentration of the hydrogen environment increases, the friction force does not increase monotonically. In addition, in a hydrogen environment, the stability of the planar structure of graphene will be weakened, thereby affecting the wrinkling effect and wear path.

A comparative study of structural properties of oleic acid coated metal nanoparticles (Co, Ni, Fe) by co-precipitation method

Metal nanoparticles of cobalt, nickel and iron were synthesized by chemical co-precipitation method using Sodium Borohydride as the reducing agent. The metallic particles were coated with oleic acid to prevent the formation of oxides on the surface layers. The structural analysis of both coated and uncoated samples were carried out using XRD technique and FTIR spectroscopy. XRD patterns of the uncoated samples showed the significant presence of oxide phases of the metallic nanoparticles while in the case of coated samples, the metallic phase was observed. A significant observation from the XRD patterns of the coated samples was the presence of a broad peak centred at 20–210 which is indicative of the graphitic structures typically observed as (002) reflections of graphite. However, the broadened peak depicted the formation of layered graphitic structures of Graphene/ nano tubes/fullerene/ nano onions. The stretching vibration of C = O and symmetric stretching vibrations of the –COO–functional group in the FTIR spectrum, indicated that the layer of oleic acid was successfully coated on the surface of MNPs. The graphitic structures of all oleic acid coated metal nanoparticles were confirmed by Raman spectroscopy. The formation of graphitic structure was the result of the catalytic action of metal nanoparticles..

Graphene based waveguide fed hybrid plasmonic terahertz patch antenna

Abstract The terahertz (THz) technology has fascinated lot of attention due to its enormous potential for a wide range of applications in the public, private and enterprise domains. This research work demonstrates the design structure and analysis of graphene based waveguide fed hybrid plasmonic THz patch antenna (HPTPA) constructed at around 3 THz. Hybrid plasmonic THz waveguide (HPTW) as a feeding line for the proposed THz patch antenna can increases antenna efficiency. The graphene is sandwiched between gallium arsenide (GaAs) and silver (Ag) to confine THz waves efficiently. Using mode analysis in finite element method for the proposed HPTW the propagation length, effective refractive index has been thoroughly examined. Based on the finite element method (FEM) approach, the results of the designed graphene-based waveguide fed HPTPA shows a high effective refractive index of 2.9, large propagation length of 230 µm, gain of 2.29 dBi, bandwidth of 200 GHz and efficiency of 85 % has obtained. The proposed graphene-based waveguide fed HPTPA could be beneficial to enable several photonic integrated circuit applications in next-generation wireless communication.

Effects of stacking layers and different doping elements on the electronic structures and quantum capacitance of graphene: A DFT study

The influence of boron (B), nitrogen (N), oxygen (O), and sulfur (S) doping on enhancing quantum capacitance were investigated through a series of the surface-doped trilayer graphene structures by using density functional theory (DFT) calculations. The quantum capacitance of monolayer models was enhanced through a single doping, a triple doping, and a vacancy defect. Our calculations suggested that the layer interactions within the trilayer models decreased the quantum capacitance but increased the stability of the doped structures. Interestingly, in the case of sulfur dopants with significantly larger atomic size than carbon, the stacking layers induced a surface distortion that could avoid the steric clashes with stacking layers and enhanced the stability. In conclusion, this work provided more realistic models of modified carbon-based electrodes for supercapacitors with more accurate information from the combined effects of doping and stacking layers.

Synthesis of crown-ether-embedded graphene by the solution plasma

Crown ethers consisting of several ether linkages (R–O–R′) have been attracting attention in the fields of inorganic and organic chemistry, attributed to their cavity sizes and superior cation selectivity. However, they exhibit comparatively low selectivity and ion-binding affinities due to their structural flexibility. Recent studies have shown that crown ethers rigidly formed within 2D matrices, e.g., graphene, exhibit enhanced binding energy and selectivity. However, most of these studies were based on computational modeling and simulations. In this study, the synthesis of crown-ether-embedded graphene was attempted for the first time by the solution plasma process (SPP). Crown-ether-embedded graphene was successfully synthesized through C–H activation and polymerization reactions between as-produced intermediates (i.e., polycyclic aromatic hydrocarbons, including multiply fused benzene rings) and activated cation radicals. Structural and chemical analyses were conducted to verify the existence of the crown ether structure (cyclic ether, C–O–C) in the carbon matrix, and a 2D graphene structure with a cavity originating from the crown ether was observed by transmission electron microscopy analysis. Moreover, adsorption test confirmed successful synthesis of crown ether-embedded graphene with ordered cavity size. We believe that the proposed synthesis approach for crown ether-embedded graphene will be valuable for a wide range of applications, such as ion-selective membrane applications and waste cleanup.

Laser-Induced Graphene Formation on Polyimide Using UV to Mid-Infrared Laser Radiation

Our study presents laser-assisted methods to produce conductive graphene layers on the polymer surface. Specimens were treated using two different lasers at ambient and nitrogen atmospheres. A solid-state picosecond laser generating 355 nm, 532 nm, or 1064 nm wavelengths and a CO2 laser generating mid-infrared 10.6 µm wavelength radiation operating in a pulsed regime were used in experiments. Sheet resistance measurements and microscopic analysis of treated sample surfaces were made. The chemical structure of laser-treated surfaces was investigated using Raman spectroscopy, and it showed the formation of high-quality few-layer graphene structures on the PI surface. The intensity ratios I(2D)/I(G) and I(D)/I(G) of samples treated with 1064 nm wavelength in nitrogen atmosphere were 0.81 and 0.46, respectively. After laser treatment, a conductive laser-induced graphene layer with a sheet resistance as low as 5 Ω was formed. Further, copper layers with a thickness of 3–10 µm were deposited on laser-formed graphene using a galvanic plating. The techniques of forming a conductive graphene layer on a polymer surface have a great perspective in many fields, especially in advanced electronic applications to fabricate copper tracks on 3D materials.

In Situ Synthesis of Doped Bio-Graphenes as Effective Metal-Free Catalysts in Removal of Antibiotics: Effect of Natural Precursor on Doping, Morphology, and Catalytic Activity.

Wastewater contaminated with antibiotics is a major environmental challenge. The oxidation process is one of the most common and effective ways to remove these pollutants. The use of metal-free, green, and inexpensive catalysts can be a good alternative to metal-containing photocatalysts in environmental applications. We developed here the green synthesis of bio-graphenes by using natural precursors (Xanthan, Chitosan, Boswellia, Tragacanth). The use of these precursors can act as templates to create 3D doped graphene structures with special morphology. Also, this method is a simple method for in situ synthesis of doped graphenes. The elements present in the natural biopolymers (N) and other elements in the natural composition (P, S) are easily placed in the graphene structure and improve the catalytic activity due to the structural defects, surface charges, increased electron transfers, and high absorption. The results have shown that the hollow cubic Chitosan-derived graphene has shown the best performance due to the doping of N, S, and P. The Boswellia-derived graphene shows the highest surface area but a lower catalytic performance, which indicates the more effective role of doping in the catalytic activity. In this mechanism, O2 dissolved in water absorbs onto the positively charged C adjacent to N dopants to create oxygenated radicals, which enables the degradation of antibiotic molecules. Light irradiation increases the amount of radicals and rate of antibiotic removal.

Crack propagation and mechanical properties simulation of G/(HfNbTaTiZr)C–Al2O3 gradient composites

The rapid development of computer simulation technology has provided theoretical and technical support for the performance prediction of ceramic materials. A two-dimensional simulation model was established to investigate the effect of the graphene (G) and gradient structure on the mechanical properties of (HfNbTaTiZr)C. Voronoi mosaics were applied in Abaqus to characterize the particle distribution of high entropy ceramics (HECs). The G/(HfNbTaTiZr)C–Al2O3 gradient ceramics were characterized through the formation of cohesive elements within grain boundaries and grains of each element using Python language. The fracture toughness, flexural strength and hardness of G/(HfNbTaTiZr)C–Al2O3 gradient ceramics were investigated through simulation model. The toughening mechanisms of G/(HfNbTaTiZr)C–Al2O3 gradient composites were investigated by establishing crack growth model. The simulation consequences are consistent with the experimental results in the literature, which verifies the accuracy of the simulation consequences. The toughening mechanism is validated through crack propagation experiments and its correctness is testified. Therefore, the simulation consequences are conducive to improving the design efficiency of HECs.

Terahertz bandwidth absorption metamaterial based on composite structure of single layer graphene

With the development of science and technology, people have realized the value of studying the terahertz band, in this paper, a terahertz bandwidth tunable metamaterial based on composite structure of single layer graphene is proposed, which can have an absorption higher than 0.9 at 3–6.7 THz and exhibit polarization insensitivity. By employing parameter inversion to calculate the relative impedance, the metamaterial adheres to the principles of impedance matching theory. The metamaterial exhibits considerable chemical and physical tuning capabilities, and it can be substantiated that the enhanced absorption rate of the metamaterial stems from a multitude of graphical configurations. Simultaneously, the metamaterial demonstrates a notable level of stability towards the incidence angle of electromagnetic waves and can function reliably at an incidence angle of 30°. In conclusion, the metamaterial holds promising potential for applications in radar stealth, communication, and other related domains.

Exploring key aspects: Structure, properties, production, and oil & gas applications of graphene and its nanoribbons − A comprehensive review

Graphene nanoribbons (GNRs) have emerged as a versatile class of nanomaterials with unique structural and electronic properties, holding immense promise for a wide range of applications. This comprehensive review paper explores the multifaceted aspects of GNRs, with a specific focus on their structural characteristics, distinctive properties, scalable production methods, and the burgeoning applications that make them particularly compelling for the oil and gas industry. The paper begins with an in-depth examination of the structural variations of Graphite, Graphene, and GNRs, delving into their width-dependent bandgap tunability, edge configurations, and atomic-level arrangements. A crucial aspect of this review is the discussion of various production methods for GNRs, encompassing bottom-up approaches like chemical vapor deposition (CVD), surface-assisted synthesis, and solution-based techniques, as well as top-down methods such as nanotube unzipping and exfoliation. The challenges and opportunities associated with scalable GNR production are thoroughly analyzed, addressing the crucial need for cost-effective and large-scale manufacturing. The primary focus then shifts to the potential applications of GNRs in the oil and gas industry. GNRs' capacity for corrosion resistance, gas sensing, catalysis, and enhanced oil recovery is scrutinized. The paper underscores their role in revolutionizing the industry by offering innovative solutions for corrosion protection, early leak detection, and improved oil extraction techniques. By bridging the gap between fundamental research and practical industry applications, it offers valuable insights for researchers, engineers, and stakeholders interested in harnessing the unique attributes of GNRs to address challenges and drive innovation in the oil and gas domain.