Multilayer Graphene Research Articles

Tuning the work function of graphite nanoparticles via edge termination.

Graphite nanoparticles are important in energy materials applications such as lithium-ion batteries (LIBs), supercapacitors and as catalyst supports. Tuning the work function of the nanoparticles allows local control of lithiation behaviour in LIBs, and the potential of zero charge of electrocatalysts and supercapacitors. Using large scale density functional theory (DFT) calculations, we find that the surface termination of multilayer graphene nanoparticles can substantially modify the work function. Calculations in vacuum and in electrolyte show that manipulating the edge termination substantially modifies the potential not only around the edge, but also on the basal plane. Termination with hydrogen or oxygen completely reverses the potential distribution surrounding the basal plane and edges. The trends can be explained based on the work function differences of the edges dependent on termination, and that of the basal plane. Electronic equilibration between different surfaces at the nanoscale allows manipulation of the work function. We demonstrate a link between the area of the graphite basal plane via changing the nanoparticle size, and the work function. We expect that these insights can be utilised for local control of electrochemical functions of graphite nanoparticles prepared under oxidising or reducing conditions.

Enhanced Detection of SF₆ Gas Moisture Concentration in Gas-Insulated Switchgear Utilizing Tilted Fiber Bragg Grating Coated With Multilayer Graphene Oxide Films

Enhanced Detection of SF₆ Gas Moisture Concentration in Gas-Insulated Switchgear Utilizing Tilted Fiber Bragg Grating Coated With Multilayer Graphene Oxide Films

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>

Nano-protrusions in intercalated graphite: understanding the structural and electronic effects through DFT.

Complex phenomena characterize the intercalation of ions inside stratified crystals. Their comprehension is crucial in view of exploiting the intercalation mechanism to change the transport properties of the crystal or obtaining a fine control of crystal delamination. In particular, the relationship between the concentration and nature of intercalated ions and surface structural modifications of the host stratified crystal is still under debate. Here, we discuss a theoretical effort to provide a rationale for some structural changes observed on the highly oriented pyrolytic graphite (HOPG) surface after electrochemical treatment in perchloric and sulphuric acid solutions. The formation of the so-called nano-protrusions on the basal plane of intercalated graphite was previously observed with scanning tunneling microscopy (STM). In this work, we employed both STM and density functional theory (DFT) simulations to elucidate the physical and chemical mechanisms driving the emergence of these nano-protrusions. The DFT results show that, in a bilayer graphene system, the presence of a single ion can generate a nano-protrusion with 2.49 Å height and 21.27 Å width. In the deformed area, the C-C bond length is stretched by about 2.5% more than the normal graphene bond. These values are of the same dimensional scale as those reported in previous STM experimental results.25 However, the simulated STM images obtained by increasing the amount of intercalated ions per area suggest that the presence of more than one ion is needed for the deformation of the uppermost graphite layer during the early stages of intercalation. In contrast, in a multilayer graphene system, no significant surface deformation is detected when ions are intercalated between the third and fourth layers. Charge analysis indicates an altered distribution of the charges as a consequence of the intercalation. The charge transfer from graphene layers to the intercalated ions results in a surface layer more prone to oxidation.

Surface modification of multilayer graphene electrodes by local printing of platinum nanoparticles using spark ablation for neural interfacing.

In this paper, we present the surface modification of multilayer graphene electrodes with platinum (Pt) nanoparticles (NPs) using spark ablation. This method yields an individually selective local printing of NPs on an electrode surface at room temperature in a dry process. NP printing is performed as a post-process step to enhance the electrochemical characteristics of graphene electrodes. The NP-printed electrode shows significant improvements in impedance, charge storage capacity (CSC), and charge injection capacity (CIC), versus the equivalent electrodes without NPs. Specifically, electrodes with 40% NP surface density demonstrate 4.5 times lower impedance, 15 times higher CSC, and 4 times better CIC. Electrochemical stability, assessed via continuous cyclic voltammetry (CV) and voltage transient (VT) tests, indicated minimal deviations from the initial performance, while mechanical stability, assessed via ultrasonic vibration, is also improved after the NP printing. Importantly, NP surface densities up to 40% maintain the electrode optical transparency required for compatibility with optical imaging and optogenetics. These results demonstrate selective NP deposition and local modification of electrochemical properties in graphene electrodes for the first time, enabling the cohabitation of graphene electrodes with different electrochemical and optical characteristics on the same substrate for neural interfacing.

Atomic and electronic structure of monolayer ferroelectric GeS on Cu(111)

Two-dimensional (2D) ferroelectric materials are important materials for both fundamental properties and potential applications. Especially, group Ⅳ monochalcogenide possesses highest thermoelectric performance and intrinsic ferroelectric polarization properties and can sever as a model to explore ferroelectric polarization properties. However, due to the relatively large exfoliation energy, the creation of high-quality and large-size monolayer group Ⅳ monochalcogenide is not so easy, which seriously hinders the integration of these materials into the fast-developing field of 2D materials and their heterostructures. Herein, monolayer GeS is successfully fabricated on Cu(111) substrate by molecular beam epitaxy method, and the lattice structure and the electronic band structure of monolayer GeS are systematically characterized by high-resolution scanning tunneling microscopy, low-energy electron diffraction, <i>in-situ</i> X-ray photoelectron spectroscopy, Raman spectra, and angle-resolved photoelectron spectroscopy, and density functional theory calculations. All atomically resolved STM images reveal that the obtained monolayer GeS has an orthogonal lattice structure, which consists with theoretical prediction. Meanwhile, the distinct moiré pattern formed between monolayer GeS and Cu(111) substrate also confirms the orthogonal lattice structure. In order to examine the chemical composition and valence state of as-prepared monolayer GeS, <i>in-situ</i> XPS is utilized without being exposed to air. The measured spectra of XPS core levels suggest that the valence states of Ge and S elements are identified to be +2 and –2, respectively and the atomic ratio of Ge/S is 1∶1.5, which is extremely close to the stoichiometric ratio of 1∶1 for GeS. To further corroborate the quality and lattice structure of the monolayer GeS film, <i>ex-situ</i> Raman measurements are also performed for monolayer GeS on highly oriented pyrolytic graphene (HOPG) and multilayer graphene substrate. Three well-defined typical characteristic Raman peaks of GeS are observed. Finally, <i>in-situ</i> ARPES measurement are conducted to determine the electronic band structure of monolayer GeS on Cu(111). The results demonstrate that the monolayer GeS has a nearly flat band electronic band structure, consistent with our density functional theory calculation. The realization and investigation of the monolayer GeS extend the scope of 2D ferroelectric materials and make it possible to prepare high quality and large size monolayer group Ⅳ monochalcogenides, which is beneficial to the application of this main group material to the rapidly developing 2D ferroelectric materials and heterojunction research.

Local stabilization of body-centred tetragonal Fe and enhanced dislocation density in carbon nanotubes filled with μm-long nanowires

We identify a variation in the predicted ABA Bernal graphitic ordering of iron-filled multiwalled carbon nanotubes, which highlights the stabilization of a high density of dislocations in samples produced by pyrolysis of low concentrations of ferrocene.

Direct localized growth of graphene on a substrate: a novel nickel-catalyzed CVD process assisted by H2 plasma.

An original metal catalyzed CVD methodology assisted by hydrogen plasma for the direct deposition of few-layer graphene on a substrate is presented. Graphene is grown at 900 °C directly on the surface of the substrate of technological interest by carbon diffusion through a nickel film by using methane (CH4) as the carbon precursor. Hydrogen atoms in the H2-plasma downstream are used to promote the solubilization of carbon atoms in Ni, thus favouring the growth of graphene at the Ni/substrate interface. Structural and transport properties of the as-grown multilayer graphene films on SiO2/Si and quartz substrates are provided. We demonstrate the peculiarity of this approach for controlling the thickness and transport properties of as-grown graphene films using process-step times. Finally, the potential of the proposed methodology for the bottom-up direct growth of patterned graphene is demonstrated.

Ready-to-use graphene-related material-added multi-grade oils: characterization and performance in car engine working conditions.

The need for energy efficiency is leading to the growing use of additives to enhance the performance of oil in automotive engines. Great interest is focused on nano-additives even if to date there is still no practical use in commercial liquid lubricants. Herein, the potential of industrially scalable and low-cost graphene-related materials (GRMs) as additives to enhance the performance of oil in automotive engines is explored. The use of polyalkylmethacrylate dispersants, the most common key additives to formulate "green technology" lubricant oils liquid-processed GRM, is explored, investigating the role of the lateral size and the chemical analysis in the stability of the lubricant GRM dispersions. Showing the maximum duration of stability and a production method that avoids the use of strong oxidants, rheological tests were then focused on multilayered graphene flakes with sub-micrometre lateral size mixed in two commercial oil grades (5W-30 and 5W-40) under conditions similar to those of engine operation. The addition of such a filler increases the viscosity without affecting the Newtonian fluid behavior, while four-ball tests show a reduction in wear, indicating improved lubrication performance. Finally, preliminary bench-test on a commercial car engine showed increased power output corresponding to enhanced engine efficiency. The results clearly indicate the effective improvement in lubricating commercial oils due to GRM additives.

In Ukrainian

The influence of the electronic subsystem of nanographene particles modified with titanium dioxide nanoparticles on the thermal destruction of the polymer matrix is analyzed. The variation in the conductivity of the modifiers made it possible to vary the effect of the metallic electronic system of graphene on thermal destruction by attenuating its effect through the transfer of energy to the electronic subsystem throughout the semiconductor film of anatase and excluding its effect on thermal destruction through a wide-band TiO2 dielectric of rutile form, which is opaque for energy transfer to the electronic subsystem. The application of such films does not affect the thermal processes in which the phonon subsystems of polymer, graphene and crystal modifiers are involved. The method of thermally programmable desorption mass spectrometry investigated the thermal destruction of hybrid composites of epoxy resin with graphene, namely the effect of surface modification of multilayer graphene particles by nanoparticles of pyrogenic titanium dioxide (anatase and rutile forms) on the thermal stability of hybrid epoxy composites in the temperature range of 40 − 800 °C. The activation energies Ed of destruction of atomic fragments of the polymer structure with the value m/z in the range of 16 ‒ 140 D were determined. It has been established that the thermal destruction of fragments of the polymer structure of epoxy resin composites with graphene modified with anatase and rutile forms of titanium dioxide is determined by the peculiarities of thermal transport at the polymer-modifier interfaces. Modification of graphene particles by the anatase form of titanium dioxide leads to increased thermal stability of polymer chains and cross-links in epoxycomposites in the entire range of m/z values of desorbed fragments. Filling the resin with graphene particles coated with the rutile form of TiO2 practically does not affect the intensity of thermal destruction of the composite matrix. The Ed values of different destruction fragments in composites with unmodified and modified graphene are in the range of 50 ‒ 130 kJ/mol. The value of Ed increases by 5 ‒ 10 kJ/mol when the resin is filled with graphene nanoparticles, while the coating of particles with titanium dioxide of the anatase and rutile phases practically does not change the value of Ed of the vast majority of fragments.

Superior Protection Conferred by Multi-Layered Graphene–Polyethylene Nanocomposites under Shock Loading

Superior Protection Conferred by Multi-Layered Graphene–Polyethylene Nanocomposites under Shock Loading

Piezoresistive performance of self-sensing cement-based composites filled with multi-layer graphene

Development of self-sensing cementitious composites is promising for structural health monitoring. This study aims at the piezoresistive performance of Multi-layer Graphene filled cement-based composites (GCBC). Experiments were conducted to evaluate the sensitivity, repeatability, linearity and hysteresis of GCBC working as a sensor under different loading systems. Percolation characteristic of GCBC, with one order of magnitude decrease in resistivity in line with the MLGs content increased from 2 vol.% to 6 vol.%, was obtained. The piezoresistive ability of GCBC containing 5 vol.% MLGs showed high sensitivity and fidelity under both cyclic and monotonic loading, with the stress sensitivity of 1.89%/MPa and gauge factor of 266.4. Meanwhile, the resistivity response of GCBC demonstrated four distinct behaviours under the monotonic loading. The piezoresistive model for GCBC dominated by tunnelling effect was proposed and compared with the experimental results. The comparative result showed good agreement between predictions with the experimental curves.

Review of: "multi-layer Si graphene field effect nano transistor, a 3D channel"

Review of: "multi-layer Si graphene field effect nano transistor, a 3D channel"

A Novel and Large-Scale Rapid Green Synthesis of Few-Layer and Multi-Layer Graphene

Mono-layer graphene has shown path-breaking potential in almost all areas that are useful to humankind. However, research in the last decade indicated that few-layer graphene (FLG) (3-10 layers) and multi-layer graphene (MLG) (>10 layers) could also be utilized for a wide range of applications. The synthesis of mono-layer graphene at a large scale is quite complex. Producing FLG and MLG at a kilogram scale is equally challenging. A vast amount of literature on different routes to prepare FLG and MLG is available. However, most of the preparation routes involve the use of hazardous chemicals, copious amounts of water, and thermal treatments and are time taking. Also, these processes need bigger machinery to convert the lab-scale methods into continuous large-scale production. On the contrary, in this work we report a novel process of producing FLG and MLG along with trace quantities of graphene (< 3 layers) developed using a kitchen mixer and a modified mixing jar (3 litres). The highlights of this process include the use of no hazardous chemicals/solvents, no washing or thermal treatment needed, much less time (30 minutes), and large quantity (250-500 grams) per batch. Our study successfully converted natural graphite flakes (NGF) into FLG and MLG by carrying out rapid liquid phase shear mixing using a green solvent. The shear mixing and the green solvent convert the NGF into FLG and MLG. The quantity of FLG and MLG getting produced is time-dependent. It has been optimized by thoroughly characterizing FLG and MLG using techniques like particle size analyser, X-ray diffraction, Raman spectroscopy, and electron microscopy. The conversion of NGF to FLG and MLG is also affirmed by studying changes in properties using tools like thermogravimetry, BET, and UV-visible spectroscopy. The developed process is rapid, efficient, economical, scalable, continuous, and, most importantly, chemical free.The graphenaceous powder produced unlike graphite can be easily coated on different substrates using appropriate binders and thus makes it useable for energy storage applications. Also the fine particle size of graphite makes is an ideal material to be used as lubricant, both in solid and liquid mediums. The developed material can be explored for its applications in several other areas which require FLG/MLG.

Effects of functionally graded graphene reinforcements on nonlinear post-local buckling and axial stiffness of laminated channel section struts

The role of local buckling on the behavior of slender members under compression has received considerable attention in structural engineering. For thin-walled sections, in particular, there is a noticeable decrease in the axial compressive stiffness, resulting in a substantial reduction in their load-bearing capacity due to the occurrence of local buckling. The principal purpose of this article is to explore the potential improvements in the postbuckling characteristics of polymeric composite channel section struts subjected to a progressive end-shortening by employing multi-layer graphene sheets reinforcements. The solution methodology incorporates the von Karman geometrical nonlinearity and is based on the layerwise third-order shear deformation theory (LW-TSDT). To verify the accuracy of the results obtained based on LW-TSDT and to evaluate its computational efficiency, a three-dimensional (3D) finite element model is also developed using ABAQUS for the comparative analysis. A thorough examination of nonlinear instability is conducted on composite laminated channel section struts, featuring distinctive graphene distribution patterns through the thickness directions of the flanges and webs to identify the most effective material distribution with the objective of a significant increase in critical end-shortening and axial compressive stiffness. The influence of the geometrical parameters on the critical end-shortening, postbuckling equilibrium paths, and load-bearing capacity of functionally graded graphene reinforced composite (FG-GRC) laminated channel section struts are elicited. The conducted parametric analyses emphasize that altering the distribution patterns of graphene reinforcement across the flanges and web can enhance the critical end-shortening and load-bearing capacity by 80% and 25%, respectively.

Competition between fractional quantum Hall liquid and electron solid phases in the Landau levels of multilayer graphene

Competition between fractional quantum Hall liquid and electron solid phases in the Landau levels of multilayer graphene

Room‐Temperature Ferromagnetism and Fermi Level Pinning in Multilayer Graphene Films Derived from Ferrocene

AbstractSpin polarization is a very important condition for spintronics applications which can easily be achieved by using ferromagnetic materials. Graphene‐based magnetic materials, which have long spin lifetime and diffusion length, are very promising as spin channel materials. In this work, Ferrocene molecules are chosen as the precursor carbon source using the chemical vapor deposition method, facilitating the synthesis of multilayer graphene films decorated with magnetic nanoclusters. This resultant material manifested planar ferromagnetism with a Curie temperature exceeding room temperature (≥300 K) and a saturation magnetization as high as 4.1 × 10−7 emu mm−2. The robust ferromagnetic coupling can plausibly be attributed to the presence of magnetic nanoclusters interspersed within the synthesized graphene, enhancing the localized magnetic moment and promoting ferromagnetic long‐range ordering. Furthermore, the Fermi level pinning at the Dirac point is observed and predominantly ascribed to the pervasive defects in the graphene derived from ferrocene. The oxygen functional groups within these defects act as charge traps, effectively anchoring the Fermi level to the Dirac point, intrinsically suppressing the ambipolar behavior of graphene. This work sheds light on potential avenues for the exploration of novel, high‐performance carbonaceous spintronics materials with economic feasibility.

The effect of surface energy on the wettability of graphene-coated copper: A comparison of different single and multilayer graphene

The present research investigated the effect of different types of graphene layers including a slow cooling rate single-layer graphene (SSLG), a high cooling rate single-layer graphene (HSLG), and a multilayer graphene (MLG) on the wettability and surface energy of the copper substrate, which was synthesized using a chemical vapor deposition (CVD) process. Results revealed an increasing trend in surface roughness of the substrate by applying the graphene layer which is mostly due to the formation of step bunches (SBs) during the synthesis process, and the highest surface roughness is obtained for the MLG. Moreover, despite the expectations the results of surface energy indicated that applying the graphene layer in all cases has increased the surface energy. However, the lowest surface energy is related to SSLG among the coated samples. On the contrary, the wettability of the coated-samples was diminished and the lowest wettability was obtained for the SSLG.

Optimization for Current-Enhanced Solid-Phase Deposition of Multi-Layer Graphene with High Crystallinity and Uniformity

Solid-phase deposition (SPD) is a preferable method to fabricate multi-layer graphene (MLG) for device applications since MLG can be deposited directly on substrates without transfer. Previously, we reported that current application during SPD enhances the MLG growth. In this study, we investigated the effects of applied current and heating rate on the crystallinity and uniformity of MLG precipitated from carbon (C) / nickel (Ni) structures. It was found that higher current and slower heating rate lead to improve the MLG crystallinity. Moreover, the uniformity was improved by the optimization of Ni and C thickness which could control the nucleation and growth of MLG during SPD. As a result, a uniform MLG with a high G/D ratio of 5.5 was obtained at a low temperature of 365 °C.

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.