Number Of Graphene Layers Research Articles

Optically driven plasmons in graphene/hBN van der Waals heterostructures: simulating s-SNOM measurements

Abstract Converting transverse photons into longitudinal two-dimensional plasmon-–polaritons (2D-PP) and vice versa presents a significant challenge within the fields of photonics and plasmonics. Therefore, understanding the mechanism which increases the photon – 2D-PP conversion efficiency could significantly contribute to those efforts. In this study, we theoretically examine how efficiently incident radiation, when scattered by a silver spherical nanoparticle (Ag-NP), can be transformed into 2D-PP within van der Waals (vdW) heterostructures composed of hexagonal boron nitride and graphene (hBN/Gr composites). We show that the Dirac plasmon (DP) excitation efficiency depends on the Ag-NP radius as R 3, and decreases exponentially with Ag-NP height h, so that for a certain Ag-NP geometry up to 25 % of the incident electrical field is channeled into the DP. We demonstrate that the linear plasmons (LPs) excitation efficiency can be manipulated by changing the graphene–graphene distance Δ (or hBN thickness) or by changing the number of graphene layers N. By increasing Δ and/or N the LPs move towards smaller wave vectors Q and become accessible by the Ag-NP dipole field, so that for N ≥ 5 the excitation of more than one LP is possible. These results are supported by recent scattering-type scanning near-field optical microscopy (s-SNOM) measurements. Furthermore, we show that Ag-NPs with specific parameters preferentially hybridizes with DPs of a particular wavelength λ D , facilitating selective excitation of DPs. The obtained tuning possibilities could have a significant impact on applied plasmonics, photonics or optoelectronics.

Hybrid graphene anti-resonant fiber with tunable light absorption.

Controlling the output light-intensity and realizing the light-switch function in hollow-core anti-resonant fibers (HC-ARFs) is crucial for their applications in polarizers, lasers, and sensor systems. Here, we theoretically propose a hybrid light-intensity-tunable HC-ARF deposited with the sandwiched graphene/hexagonal boron nitride/graphene based on the typical six-circular-tube and the nested structures. Changing the external drive voltage from 12.3 to 31.8 V, the hybrid HC-ARF experiences a high-low alterative attenuation coefficient with a modulation depth 3.87 and 1.91 dB/cm for the six-circular-tube and nested structures respectively, serving as a well-performance light-switch at the optical communication wavelength of 1.55 µm. This response is attributed to the variation of the Fermi level of graphene and is obviously influenced by the core size, fiber length, and the number of graphene and hBN layers. Moreover, one attenuation dip of the modulation depth was found because of the epsilon-near-zero effect in graphene. Our design provides a feasible paradigm for integrating graphene with anti-resonant fibers and high-performance electro-optic modulators.

Wood-Derived Graphite: A Sustainable and Cost-Effective Material for the Wide Range of Industrial Applications

The study explored the graphitization of wood through two distinct methods: a high-temperature approach at 2400 °C and a low-temperature technique at 1400 °C using a catalyst. The graphitization properties were assessed by conducting thermal experiments at various temperatures (1100 °C, 1400 °C, 1800 °C, 2000 °C, and 2400 °C), both with and without a catalyst. The development of graphite lattices was quantitatively analyzed using an array of techniques: X-ray diffractometer (XRD), Raman spectroscopy, high-resolution transmission electron microscopy (HR-TEM), and Fourier transform infrared spectroscopy (FTIR). The XRD analysis highlighted temperature-dependent changes in lattice parameters (d002, La, and Lc), while Raman spectroscopy tracked alterations in the D to G peak ratio (D/G) with temperature. An increase in temperature is correlated with a rise in the number of graphene layers and the degree of graphitization. Notably, the process of graphite lattice formation varied across the experimental temperature spectrum. The use of a catalyst resulted in a reduced d002 spacing, signifying an enhanced degree of graphitization. Moreover, the catalyst promoted a consistent and smooth graphitization process throughout the heating stages. In contrast, graphitization without a catalyst occurred at higher temperatures, specifically between 1800 °C and 2000 °C, with the d002 value stabilizing around 0.338 nm. The catalyst proved instrumental in transforming the initial structure into well-ordered graphite at lower temperatures. This investigation underscores the potential and benefits of employing a catalyst to generate high-quality graphite from wood at reduced temperatures, paving the way for sustainable and economically viable applications of this material.

Measuring the Capacitance of Carbon in Ionic Liquids: From Graphite to Graphene.

The physical electrochemistry of the carbon/ionic liquids interface underpins the processes occurring in a vast range of applications spanning electrochemical energy storage, iontronic devices, and lubrication. Elucidating the charge storage mechanisms at the carbon/electrolyte interface will lead to a better understanding of the operational principles of such systems. Herein, we probe the charge stored at the electrochemical double layer formed between model carbon systems, ranging from single-layer graphene to graphite and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI). The effect of the number of graphene layers on the overall capacitance of the interface is investigated. We demonstrate that in pure EMIM-TFSI and at moderate potential biases, the electronic properties of graphene and graphite govern the overall capacitance of the interface, while the electrolyte contribution to the latter is less significant. In mixtures of EMIM-TFSI with solvents of varying relative permittivity, the complex interplay between electrolyte ions and solvent molecules is shown to influence the charge stored at the interface, which under certain conditions overcomes the effects of relative permittivity. This work provides additional experimental insights into the continuously advancing topic of electrochemical double-layer structure at the interface between room temperature ionic liquids and carbon materials.

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

AbstractLarge area single and bilayer graphene are grown on Pt/Ti/SiO2 substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO2 substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO2 substrate at a low filament temperature. The approach paves a novel pathway towards the layer‐controlled growth of graphene on Pt/Ti/SiO2 substrates by HFCVD for frontier applications.

First-principle study of spin transport property in L10-FePd(001)/graphene heterojunction

In our previous work, we synthesized a metal/2D material heterointerface consisting of L10-ordered iron–palladium (FePd) and graphene (Gr) called FePd(001)/Gr. This system has been explored by both experimental measurements and theoretical calculations. In this study, we focus on a heterojunction composed of FePd and multilayer graphene referred to as FePd(001)/m-Gr/FePd(001), where m represents the number of graphene layers. We perform first-principles calculations to predict their spin-dependent transport properties. The quantitative calculations of spin-resolved conductance and magnetoresistance (MR) ratio (150%–200%) suggest that the proposed structure can function as a magnetic tunnel junction in spintronics applications. We also find that an increase in m not only reduces conductance but also changes transport properties from the tunneling behavior to the graphite π-band-like behavior. Additionally, we investigate the spin-transfer torque-induced magnetization switching behavior of our junction structures using micromagnetic simulations. Furthermore, we examine the impact of lateral displacements (sliding) at the interface and find that the spin transport properties remain robust despite these changes; this is the advantage of two-dimensional material hetero-interfaces over traditional insulating barrier layers such as MgO.

Peridynamics for the fracture study on multi-layer graphene sheets

Understanding the fracture properties of graphene sheets is a crucial step towards their practical applications. However, due to the limitations of experimental operations and all-atom (AA) methods, investigating the fracture of large-sized nano graphene sheets remains a formidable challenge. Especially, study on the layer-by-layer fracture of multi-layer graphene sheets (MLGS) is nearly impossible. To overcome this challenge, a peridynamic (PD) model is proposed in this study, which comprises the intra-layer part and the inter-layer part. The proposed PD model is validated by comparing the fracture toughness and the fracture forms of MLGS with existing experiments. It is found that the uniaxial tensile stress-strain curve of pre-cracked MLGS is closely related to the number of graphene layers in MLGS. The fracture property of MLGS can be enhanced by increasing the number of graphene layers, reducing the pre-crack length and blunting the pre-crack tip. Notably, asynchronous crack propagation with independent path observed in MLGS is a unique mechanism for strengthening the fracture property, which is distinct from monolayer graphene sheet. In this work, the PD theory is extended for the first time to investigate the in-plane fracture of large-sized nano MLGS.

Experimental study and modeling of the wettability of fluorine graphene. Corrosion behavior of the fluorine graphene layer on a copper substrate

Fluorographene (FG) is a high-quality 2D insulator, which is effectively used as the atomically thin tunnel barrier. To date, the most common idea is that the complete fluorination of graphene (G) leads to an increase in hydrophobicity. We have shown that in reality fluorination leads to superhydrophilicity and to a significant increase in the defectiveness of the graphene layer. Without hydrocarbons, as well as due to the high defectiveness and superhydrophilicity, the corrosion current of FG is an order of magnitude higher than for pure copper and two orders of magnitude higher than for G synthesized on copper. The simulation results confirm experimental data on FG superhydrophilicity after prolonged fluorination. Thus, in order to achieve high hydrophilicity, it is not necessary to create hydroxyl groups on the surface of FG. A higher concentration of fluorine (the C/F composition ratio) is realized on a thicker copper plate with a graphene layer, compared to thin copper foil. Different fluorine concentrations are associated with different sizes of crystal grains, their orientation, as well as defectiveness and the number of graphene layers. The corrosive effect leads to a decrease in roughness and a multiple decrease in the amount of F on the FG.

Degradation of Graphene in High- and Low-Humidity Air, and Vacuum Conditions at 300-500 K.

Graphene is a fundamental unit of carbon materials and, thus, primary sp2-bonded carbon material. Graphene is, however, easily broken macroscopically despite high mechanical strength, although its natural degradation has rarely been considered. In this work, we evaluate the natural degradation of two-layer graphene in vacuo, in low-humidity air, and in high-humidity air at 300, 400, 450, and 500 K. Over 1000 days of degradation at 300 K, the graphene structure was highly maintained in vacuo, whereas the layer number of graphene tended to decrease in high- and low-humidity air. Water was slightly reacted/chemisorbed on graphene to form surface oxygen groups at 300 K. At 450 and 500 K, graphene was moderately volatilized in vacuo and was obviously oxidized in high- and low-humidity air. Surprisingly, the oxidation of graphene was more suppressed in the high-humidity air than in the low-humidity air, indicating that water worked as an anti-oxidizer of graphene by preventing the chemisorption of oxygen on the graphene surface.

Machine Learning-Assisted Identification of Single-Layer Graphene via Color Variation Analysis.

Techniques such as using an optical microscope and Raman spectroscopy are common methods for detecting single-layer graphene. Instead of relying on these laborious and expensive methods, we suggest a novel approach inspired by skilled human researchers who can detect single-layer graphene by simply observing color differences between graphene flakes and the background substrate in optical microscope images. This approach implemented the human cognitive process by emulating it through our data extraction process and machine learning algorithm. We obtained approximately 300,000 pixel-level color difference data from 140 graphene flakes from 45 optical microscope images. We utilized the average and standard deviation of the color difference data for each flake for machine learning. As a result, we achieved F1-Scores of over 0.90 and 0.92 in identifying 60 and 50 flakes from green and pink substrate images, respectively. Our machine learning-assisted computing system offers a cost-effective and universal solution for detecting the number of graphene layers in diverse experimental environments, saving both time and resources. We anticipate that this approach can be extended to classify the properties of other 2D materials.

Unraveling the effects of geometrical parameters on dynamic impact responses of graphene reinforced polymer nanocomposites using coarse-grained molecular dynamics simulations.

Nacre plays an important role in bionic design due to its light weight, high strength, and structure-function integration. The key to elucidate its reinforcing and toughening mechanisms is to truly characterize its multi-layer structure and properties. In this work, the dynamic impact responses of graphene reinforced polymer nanocomposites with a unique brick-and-mortar structure are investigated using coarse-grained molecular dynamics simulations, in which the interfacial coarse-grained force field between graphene and the polymer matrix is derived by the energy matching approach. The influences of various geometrical parameters on dynamic impact responses of the nanocomposites are studied, including the interlayer distance, lateral distance, and number of graphene layers. The results demonstrate that the impact resistance of the nacre-like structure can be significantly improved by tuning the geometrical parameters of graphene layers. It is also found that the chain scission and interchain disentanglement of polymer chains are the main failure mechanisms during the perforation failure process as compared to the stretching and breaking of bonds. In addition, the microstructure analysis is performed to deeply interpret the deformation and damage mechanisms of the nanocomposites during impact. This study could be helpful for the rational design and preparation of graphene reinforced nacre-like nanocomposites with high impact resistance.

2D diamond structures in multilayer graphene: Simulation and experimental observation

The presented paper investigates the formation of nanodiamond structures within multilayer graphene through irradiation with fast heavy ions. The study demonstrates that Xe26+ ions with energies ranging from 26 to 167 MeV can create diamond regions in graphene with lateral sizes ranging from 5 to 20 nm. The density of nanodiamonds formed in the few-layer graphene films is estimated to be approximately (5–30)% of the ion fluence. We show that the final structure of the diamond structures is influenced by factors such as surface orientation, number of graphene layers, and lateral size. Atomistic simulations predicted unusual mechanical properties of the formed 2D composite: its Young's modulus obtained by indentation can significantly exceed the stiffness of the original graphene film.

Interfacial thermal conductance of gallium nitride/graphene/diamond heterostructure based on molecular dynamics simulation

<sec>Gallium nitride chips are widely used in high-frequency and high-power devices. However, thermal management is a serious challenge for gallium nitride devices. To improve thermal dissipation of gallium nitride devices, the nonequilibrium molecular dynamics method is employed to investigate the effects of operating temperature, interface size, defect density and defect types on the interfacial thermal conductance of gallium nitride/graphene/diamond heterostructure. Furthermore, the phonon state densities and phonon participation ratios under various conditions are calculated to analyze the interface thermal conduction mechanism.</sec><sec>The results indicate that interfacial thermal conductance increases with temperatures rising, highlighting the inherent self-regulating heat dissipation capabilities of heterogeneous. The interfacial thermal conductance of monolayer graphene structures is increased by 2.1 times as the temperature increases from 100 to 500 K. This is attributed to the overlap factor increasing with temperature rising, which enhances the phonon coupling between interfaces, leading the interfacial thermal conductance to increase.</sec><sec>Additionally, in the study it is found that increasing the number of layers of both gallium nitride and graphene leads the interfacial thermal conductance to decrease. When the number of gallium nitride layers increases from 10 to 26, the interfacial thermal conductance decreases by 75%. The overlap factor diminishing with the layer number increasing is ascribed to the decreased match of phonon vibrations between interfaces, resulting in lower thermal transfer efficiency. Similarly, when the number of graphene layers increases from 1 to 5, the interfacial thermal conductance decreases by 74%. The increase in graphene layers leads the low-frequency phonons to decrease, consequently lowering the interfacial thermal conductance. Moreover, multilayer graphene enhances phonon localization, exacerbates the reduction in interfacial thermal conductance.</sec><sec>It is found that introducing four types of vacancy defects can affect the interfacial thermal conductance. Diamond carbon atom defects lead its interfacial thermal conductance to increase, whereas defects in gallium, nitrogen, and graphene carbon atoms cause their interfacial thermal conductance to decrease. As the defect concentration increases from 0 to 10%, diamond carbon atom defects increase the interfacial thermal conductance by 40% due to defect scattering, which increases the number of low-frequency phonon modes and expands the channels for interfacial heat transfer, thus improving the interfacial thermal conductance. Defects in graphene intensify the degree of graphene phonon localization, consequently leading the interfacial thermal conductance to decrease. Gallium and nitrogen defects both intensify the phonon localization of gallium nitride, impeding phonon transport channels. Moreover, gallium defects induce more severe phonon localization than nitrogen defects, consequently leading to lower interfacial thermal conductance.</sec><sec>This research provides the references for manufacturing highly reliable gallium nitride devices and the widespread use of gallium nitride heterostructures.</sec>

Molecular dynamics simulation of mechanical strengthening properties of SiC substrate covered with multilayer graphene

A large number of practices have shown that under the coupling influence of complex working conditions and frequent reciprocating contact, the surfaces of semiconductor devices in micro/nano electromechanical systems often produce adhesive wear, which is the essential reason resulting in short durability service life and declining contact mechanical properties for microelectronics semiconductor devices. However, graphene can significantly improve the interface properties of mechanical components and electronic components due to its excellent mechanical properties, such as high carrier concentration, good thermal conductivity, and low shear. Thus, the study of mechanical strengthening properties and plastic deformation of SiC material with covered multi-layer graphene in MEMS devices will play a significant role in improving the durability service life of MEMS device, and understanding its strengthening and toughening mechanism. Therefore, this paper studies and discusses the effects of stacking type and extreme service temperature with low and high levels on the contact mechanical properties (maximum load, hardness, Young modulus, contact stiffness), micro-structure evolution, contact mass, fold morphology, and total length of dislocation. The atomic-scale mechanism of enhanced mechanical properties of SiC material with multi-layer graphene is explained. The research shows that the damage to carbon-carbon bond at the maximum indentation depth will lead graphene to lose the excellent in-plane elastic deformation capability when the graphene stacking type is AB stacking, so that the maximum load-bearing capacity of the substrate covered by three layers of graphene will drop linearly. In addition, the mechanical property of SiC material coated with three graphene layers is twice that of pure SiC substrate, and the strengthening mechanism is mainly due to the increase of wrinkle caused by the increase of multilayer graphene loading, which causes the quality of contact between the SiC substrate and the virtual indenter to decrease, thus increasing the interface contact stiffness. The increase of the active temperature will trigger off the increase of the atomic vibration frequency, which will cause the number of interface contact atoms to increase greatly, and the interface contact stiffness will weaken, and finally lead the interface contact quality to improve, This is because the mechanical properties of SiC substrate coated with multilayer graphene will decrease approximately linearly with the extreme service from low temperature to high temperature. In addition, the stress concentration in the subsurface layer of SiC substrate can induce the evolution of its micro-structure, and the increase of the number of graphene layers on the substrate can effectively reduce the stress concentration distribution in the subsurface layer of the substrate.

Expanding the range of graphene energy transfer with multilayer graphene.

The interaction between single emitters and graphene in the context of energy transfer has attracted significant attention due to its potential applications in fields such as biophysics and super-resolution microscopy. In this study, we investigate the influence of the number of graphene layers on graphene energy transfer (GET) by placing single dye molecules at defined distances from monolayer, bilayer, and trilayer graphene substrates. We employ DNA origami nanostructures as chemical adapters to position the dye molecules precisely. Fluorescence lifetime measurements and analysis reveal an additive effect of graphene layers on the energy transfer rate extending the working range of GET up to distances of approximately 50-60 nm. Moreover, we show that switching a DNA pointer strand between two positions on a DNA origami nanostructure at a height of >28 nm above graphene is substantially better visualized with multilayer graphene substrates suggesting enhanced capabilities for applications such as biosensing and super-resolution microscopy for larger systems and distances. This study provides insights into the influence of graphene layers on energy transfer dynamics and offers new possibilities for exploiting graphene's unique properties in various nanotechnological applications.

Role of Graphene-related 2D Nanomaterials in Antimicrobial Potentials: An Overview

Microbial infections profoundly impact various facets of everyday life, imposing significant economic strains on healthcare systems worldwide and resulting in death. Researchers have made considerable attempts to restrict microbial proliferation, but effective antimicrobial agents still need to be improved. A highly effective strategy for mitigating this challenge involves utilizing antimicrobial materials with chemically embedded or inherent antimicrobial properties. Recently, carbon-based nanomaterials have shown promising antibacterial results. In particular, graphene- and graphene-derived nanomaterials (GMs) demonstrate a broad range of antimicrobial activity against bacteria, fungi, and viruses. These antibacterial activities are attributed mainly to the direct physicochemical interaction between GMs and bacteria that cause deadly cellular component degradation. GMs hold a high affinity for accumulating, leading to membrane damage; similarly, after internalization, they can interact with the bacterial genome, disrupting the replicative stage. Additionally, GMs can indirectly determine bacterial death by activating the inflammatory cascade after entering the physiological environment. This mini-review delves into the potential parameters influencing antimicrobial efficacy, encompassing the number of graphene layers, concentration, size, and structural characteristics. Additionally, it explores the antimicrobial mechanisms exhibited by the graphene family against a spectrum of pathogens. Finally, it presents various antimicrobial applications underlying GMs as promising materials applicable in different fields.

Molecular dynamics study of interfacial thermal transport properties of graphene/GaN heterostructure

The performance of interfacial thermal transport in heterostructure determines the reliability of micro- and nano-scale device. In this study, a molecular dynamics method is used to investigate the interfacial thermal transport properties of graphene/GaN sandwich heterostructure. The effects of temperature, defect, and size on the interface thermal conductance at the heterostructure are analyzed. It is found that the interface thermal conductance increases with temperature rising; at 1100 K, the interface thermal conductance of the 3-layer graphene heterostructure is increased by 61%. This increase is mainly attributed to the enhanced lattice vibrations at higher temperature, which excites more out-of-plane phonons. The presence of minor vacancy defects in GaN leads interface thermal conductance to increase, reaching a maximum value of 0.0357 GW/(m<sup>2</sup>·K) at a defect rate of 20%. This enhancement is believed to be due to additional thermal transport pathways created by the defects. However, as the defect rate increases further, the interface thermal conductance begins to decrease, which is thought to be due to interfacial coupling strength decreasing. With the number of GaN layers increasing from 8 to 24, the interface thermal conductance decreases, the change is attributed to the decrease of the number of phonons participating in the thermal transport across the interface. Conversely, with the number of graphene layers increasing from 2 to 6, the interface thermal conductance initially increases and then decreases. This behavior is related to initial improvements of phonon matching and coupling strength, followed by the increase in phonon scattering and localization. The results of this study provide a theoretical basis for regulating the interfacial thermal transport in microelectronic devices.

In-situ fracture toughness measurement of multilayer graphene

Understanding the fracture and failure properties of graphene is a critical step towards integrating graphene into electromechanical devices and flexible electronics. However, the exact fracture properties of graphene are hard to measure due to the atomic level thickness of graphene and its brittle nature which tends to cause it to break before accurate measurements of its properties can be made. In this paper, a method is presented for measuring the fracture properties of graphene with varying number of layers. This method utilizes a custom designed MEMS tensile tester and an effective and repeatable graphene transfer process that enables the transfer of patterned graphene structures onto MEMS devices. The fracture properties of graphene samples with different numbers of graphene layers were tested and the critical strain energy release rate of fracture was measured to be 22 J/m2, 71.3 J/m2, and 145 J/m2 for ∼ 7 layer, ∼12 layer, and ∼ 15 layer graphene, respectively. These results show that the fracture toughness of the graphene increases as the number of layers increases. This is likely due to the need for brittle cracks to propagate through multiple, weakly connected layers of the graphene for ultimate failure to occur in the graphene.

Direct growth of few-layered graphene on boron doped diamond surface with varying boron doping concentration

The diamond-graphene heterostructure is a promising all‑carbon composite structure, which can take advantages of excellent properties of these two materials. At present, the diamond-graphene heterojunction were mostly synthesized by chemical vapor deposition (CVD) method with intrinsic diamond substrate. In this study, the few-layered graphene is synthesized on boron-doped-diamond (BDD) surface through a simple thermal treatment method with Ni catalyst. The effects of boron doping concentration of substrate on the synthesis of diamond-graphene heterojunctions is studied. It demonstrates that the surface morphology and roughness are improved with the increasing of substrate doping concentration. Compared with the light doped and un-doped diamond, the number of graphene layers and quality decreases and increases, respectively.

Positronium transmission through graphene thin films supported with lacy carbon in the energy range of a few keV

We studied the transmission of positronium through thin graphene films supported with lacy carbon using an energy-tunable positronium beam recently developed based on photodetachment of positronium negative ions. By analysing the results of the measurements conducted with different number of graphene layers, the transmittance per single-layer graphene without lacy carbon was estimated to be 70% and 74% at 2.3 keV and 3.3 keV, respectively.Graphical