Few-layer Graphene Research Articles

Rheology of Conductive High Reactivity Carbonaceous Material (HRCM)-Based Ink Suspensions: Dependence on Concentration and Temperature.

The present case study reports a shear rheological characterization in the temperature domain of inks and pastes loaded with conductive High Reactivity Carbonaceous Material (HRCM) consisting mainly of few-layers graphene sheets. The combined effect of filler concentration and applied shear rate is investigated in terms of the shear viscosity response as a function of testing temperature. The non-Newtonian features of shear flow ramps at constant temperature are reported to depend on both the HRCM load and the testing temperature. Moreover, temperature ramps at a constant shear rate reveal a different viscosity-temperature dependence from what is observed in shear flow ramps while maintaining the same filler concentration. An apparent departure from the well-known Vogel-Fulcher-Tamman relationship as a function of the applied shear rate is also reported.

Easy and Versatile Synthesis of Bulk Quantities of Highly Enriched 13C-Graphene Materials for Biological and Safety Applications.

The preparation of bulk quantities of 13C-labeled graphene materials is relevant for basic investigations and for practical applications. In addition, 13C-labeled graphene materials can be very useful in biological and environmental studies, as they may allow the detection of graphene or its derivatives in cells or organs. In this paper, we describe the synthesis of 13C-labeled graphene materials (few-layer graphene, FLG, and graphene oxide, GO) on a tens of mg scale, starting from 13C-labeled methane to afford carbon fibers, followed by liquid-phase exfoliation (FLG) or oxidation (GO). The materials have been characterized by several analytical and microscopic techniques, including Raman and nuclear magnetic resonance spectroscopies, thermogravimetric analysis, X-ray photoelectron spectroscopy, and X-ray powder diffraction. As a proof of concept, the distribution of the title compounds in cells has been investigated. In fact, the analysis of the 13C/12C ratio with isotope ratio mass spectrometry (IRMS) allows the detection and quantification of very small amounts of material in cells or biological compartments with high selectivity, even when the material has been degraded. During the treatment of 13C-labeled FLG with HepG2 cells, 4.1% of the applied dose was found in the mitochondrial fraction, while 4.9% ended up in the nuclear fraction. The rest of the dose did not enter into the cell and remained in the plasma membrane or in the culture media.

Buckling Behavior of Few-Layer Graphene on Soft Substrate

The buckling behavior of graphene on soft films has been extensively studied. However, to avoid graphene fracture, most studies focus only on the primary buckling behavior induced by tiny compression. Here, the buckling behavior of monolayer, three-layer, and four-layer graphene on soft films is systematically studied in the experiment under large compression. The cross-sections of buckling patterns in these few-layer graphenes are provided, which depend on focused ion beam (FIB) technology. More significantly, the moduli of few-layer graphene are calculated based on the buckling behavior. We demonstrate that the modulus, 1.12621 TPa, is independent of the number of graphene layers if the number is less than four. Our investigations are crucial for the application of two-dimensional (2D) materials into flexible hybrid electronics, bionics, and various other stiff/soft bilayer systems.

Morphological features and photoluminescence of ZnO and ZnO decorated S,N-doped few-layered graphene (ZnO–S, N-FLGs)

Zinc oxide (ZnO) nanoparticles and ZnO decorated S, N doped few-layered graphene (1 wt%, 2 wt%, and 3 wt %) were synthesized using a simple chemical method followed by calcination. The chemical composition, morphology, lattice vibrations, and distinct structural features of the ZnO and ZnO–S,N-FLGs composites have been characterized by X-ray diffraction (XRD) and μ-Raman spectroscopy. X-ray diffraction (XRD) patterns conform that the pristine ZnO nanostructures and ZnO–S,N-FLGs composites were formed. Electron microscopic techniques (FESEM & TEM) were employed to observe the morphologies. Field emission electron microscope (FESEM) images showed that different morphologies of ZnO nanostructures were decorated on S,N-FLGs sheets. Transmission electron microscope (TEM) images exposed that ZnO different morphologies were uniformly distributed on S,N-FLGs sheets. However, the TEM images showed that nanocomposites' morphology changed significantly with increased S,N-FLGs concentration. The results showed that ZnO with different morphologies was well dispersed on the S,N doped FLGs, which serve as ZnO nanoparticle growing supports and the morphology controller. The Raman shift of the 2D peak shows the interaction between ZnO and S,N-FLGs. It was found that control of the incorporated functional groups of the S,N-FLGs with the assistance of calcination temperature during the synthesis. The morphology of ZnO, such as hexagonal, nanorods, and nanospheres (1 wt%, 2 wt%, and 3 wt% S,N-FLGs). The bandgap of all the synthesized materials was calculated by UV–vis spectroscopy (UV–vis). The photoluminescence (PL) spectra were measured at room temperature (RT). The intensity of peaks of ZnO–S, N-FLGs composites decreased compared to ZnO in PL spectra because of oxygen vacancies and defects. The intense UV emission indicates interesting optical properties were reported in detail.

Plasma Electrochemical Synthesis of Graphene-Phosphorene Composite and Its Catalytic Activity towards Hydrogen Evolution Reaction

For the first time, graphene-phosphorene structures were synthesized using the plasma-assisted electrochemical method. The catalytic activity of the composite obtained in the electrolytic plasma mode and its mixtures with few-layer graphene structures toward the hydrogen evolution reaction was studied. A substantial increase in the catalytic activity of the phosphorene structures towards the hydrogen evolution reaction was realized by mixing them with few-layer graphene structures. The catalyst demonstrates excellent activity towards the hydrogen evolution reaction in alkaline media with a low overpotential of 940 mV at a current density of 10 mA·cm−2 and a small Tafel slope of 130 mV dec−1.

High-Surface-Area Graphene Oxide for Next-Generation Energy Storage Applications

Synthesis of high-surface-area graphene oxide for application in next-generation devices is still challenging. In this study, we present a simple and green-chemistry procedure for the synthesis of oxygen-enriched graphene materials, having very large surface areas compared with those reported for powdered graphene-related solids. Using the hydrothermal treatment of carbon nanohorns by a green-chemistry H2O2 oxidant under elevated pressure, the progressive creation of a stable carbon nanomaterial, denoted as open-sensu-shaped graphene oxide (OSSGO) by us, is observed. This oxygen-enriched nanographene contains π–π stacked few-layered graphene ribbons curved at the termini derived from the original cone tip. OSSGO is intensively analyzed and cross-characterized by spectroscopy, diffraction, adsorption, and elemental analysis methods. Based on the obtained results, we propose a mechanism of transformation from horns to a structure with several layers of sensu-form stacked graphene oxide. As this transformation process proceeds gradually, one can obtain numerous transition nanoarchitectures of tunable morphology and surface physicochemistry, including materials with an extremely high surface area. As OSSGO bears a fraction of the electron-withdrawing and O–H acidic functionalities, electrochemical studies, especially galvanostatic charge–discharge curves and specific capacitance values (significantly higher than those for other carbon-based materials), show potential applications in next-generation supercapacitors. As a result of the large surface areas, we also predict future applications in programmable adsorbents and catalysts with broad-range activity, while the list of applications is incomplete.

Superior Thermal Conductivity of Graphene Film/Cu-Zr Alloy Composites for Thermal Management Applications.

As the power density of electronic devices continuously increases, there is a growing demand to improve the heat conduction performance of thermal management materials for addressing heat dissipation issues. Single-/few-layer graphene is a promising candidate as a filler of a metal matrix due to its extremely high thermal conductivity (k); however, the well-arranged assembly of 2D-component graphene with a high volume fraction remains challenging. Herein, we integrated a novel graphene-based macroscopic material of graphene film (GF) into a Cu matrix by infiltrating molten Zr-microalloyed Cu into a spirally folded and upright-standing GFs skeleton. The microstructure of the GF/Cu composites was regulated by an interface modification strategy. The GF/Cu composites with a spirally layered microstructure exhibit a superior k of 820 W/m K in the axial direction, much higher than that of Cu-matrix composites reinforced with graphene nanosheets (generally <500 W/m K) and twice that of Cu. The thermal transfer mechanisms were investigated by experiments and theoretical calculations. The results reveal that the excellent performance is attributed to the construction of high-heat conduction channels and a positive coordinating effect at the Zr-modified GF/Cu interface. Meanwhile, the relation between interfacial microstructure and heat transfer is established in the composites using interfacial thermal resistance as a bridge. This work yields in-depth insight into the heat conduction mechanism in highly oriented structures and provides a promising solution for the thermal management issues of high-power electronics.

Resuscitation of spent graphite anodes towards layer-stacked, mechanical-flexible, fast-charging electrodes

The alarming resource shortage of the lithium battery supply chain has triggered new vitality to the close-loop recycling of retired batteries. As compared to hydrometallurgy or pyrometallurgy strategies for the cathode recovery, the proper use of degraded graphite anodes, featuring with the solvated Li+ intercalation and in-plane defect formation, is hitherto neglected. In this work, we propose a facile “green route” to extract values from spent graphite anode. Through elucidating the dynamic Li occupancy in graphite lattice, an up-scaling delamination protocol is developed with the aid of in-situ generated H2 bubbles in the protic mixed solvent, to weaken van der Waals (vdW) bonding of the graphite interlayers and generate few-layer graphene flakes (∼ 2 nm); meanwhile high-purity Li salt could be simultaneously extracted from the residue solvent (∼ 98% Li leaching efficiency). Upon exquisite interfacial modification, the as-exfoliated graphene flakes tend to assemble with the Na2Ti6O13 (NTO) nanosheets as a layer-stacked, mechanical-flexible anode, which further demonstrates a robust cycling at various flexing states and extreme power output of 1142 Wkg−1 as paired with the LiFePO4 cathode (5.3 mg cm−2) in the integrated, thin-film battery. This work vividly demonstrates potential add-value market of spent anodes in the flexible power sources.

A unified framework of slip controlled bending and rippled superlattice design of few-layer graphene

The out-of-plane bending of few-layer graphene (FLG) and other 2D materials have attracted increasing attention due to its practical significance in flexible electronics and soft robotics. Extensive studies have been carried out establishing the crucial role interlayer slip plays in the bending of FLG. Yet in previous analysis, slip was treated as the consequence of bending, rather than an independent variable, which makes sense physically but shadows part of its functionality. Here through a novel atomic simulation scheme, we select desired slip ratios r, a term we defined to quantify the ratio of the actual amount of slip to the maximum amount. The slip ratio serves as a gauge for determining the predominant deformation mechanism in curved FLG. We identified three regimes characterized with critical slip ratios rc* and rth. When r > rc*, FLG behaves like the monolayer, and curvature is the primary quantity during its deformation. As r drops below rc*, the accumulated in-plane strain imposes more impact, while when r < rth, buckling and delamination may occur. By manipulating slip, we predict non-classical low-energy rippled superlattice of FLG, characterized by minimum periodicities, as small as a few nanometers, smaller than the FLG thickness itself.

Sulfonated cobalt phthalocyanine-stabilized graphene: Ultrasonic exfoliation and application in anticorrosion of aluminum

Aqueous phase exfoliation (APE) has become a promising method of the graphene preparation. However, it still has some disadvantages, such as low yield and the influence of residual stabilizer on its application. Herein we report a method of the graphene preparation via APE of graphite assisted by sulfonated cobalt phthalocyanine (CoPcS) as the stabilizer. A high yield of graphene can be obtained at low concentration of CoPcS. The yield was 3.2 % in single exploitation, and the total yield reached to 7.3 % after three cycles of exfoliation. The sizes of the prepared graphene sheets were in micron level, and the percentage of few-layer graphene (<5) reached 93 %. The π-π interaction of graphene with CoPcS, as well as the repulsive interaction between negatively charged CoPcS ions, played a crucial role in stabilizing the graphene dispersion. The as-exfoliated graphene powder served directly as a filler in the epoxy coating on the surface of aluminum to improve the protection performance of the coating. A simple, cost-effective, and potential avenue has been provided to product and utilize high-quality graphene materials.

Electrical performance of orthotropic and isotropic 3YTZP composites with graphene fillers

3 mol% yttria tetragonal zirconia polycrystal (3YTZP) composites with orthotropic or isotropic microstructures were obtained incorporating few layer graphene (FLG) or exfoliated graphene nanoplatelets (e-GNP) as fillers. Electrical conductivity was studied in a wide range of contents in two configurations: perpendicular (σꓕ) and parallel (σ//) to the pressing axis during spark plasma sintering (SPS). Isotropic e-GNP composites presented excellent electrical conductivity for high e-GNP contents (σꓕ ∼ 3200 S/m and σ// ∼ 1900 S/m for 20 vol% e-GNP), consequence of their misoriented distribution throughout the matrix. Optimum electrical performance was achieved in the highly anisotropic FLG composites, with high electrical conductivity for low contents (σꓕ ∼ 680 S/m for 5 vol%), percolation threshold below 2.5 vol% FLG and outstanding electrical conductivity for high contents (σꓕ ∼ 4000 S/m for 20 vol%), result of the high aspect ratio and low thickness of FLG.

Production of graphene-derivatives using organic molecules for supercapacitors and beyond

Graphene is rapidly expanding for applications ranging from nanoelectronics to space exploration. A material with such enormous potential requires a variety of synthesis methods. Here, we report a library of relatively sustainable redox-active organic molecules for the reduction of graphene oxide (GO) namely N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), 7,7,8,8-tetracyanoquinodimethane (TCNQ), ferrocene (Ferro), and decamethylferrocene (DFerro). Among them, the reduction of GO using TMPD starts even with simple hand-shaking for just a few minutes. By controlling the sonication time under ambient conditions, one can control the electronic properties of the reduced graphene oxide (rGO). The resulting free-standing films delivered a capacitance of 185 F/g when tested them as supercapacitor electrodes. We also demonstrated that TMPD can exfoliate graphite into few-layer graphene sheets with simple sonication. We further show that under mild heating, these molecules can serve as dopants during the reduction process to produce nitrogen-doped graphene. Our results may guide researchers to explore sustainable organic molecules for the large-scale production of graphene-based materials for diverse applications.

Mechanically Strong and Electrically Conductive Polyethylene Oxide/Few-Layer Graphene/Cellulose Nanofibrils Nanocomposite Films

In this work, a cellulose nanofibrils (CNFs)/few-layer graphene (FLG) hybrid is mechanically stripped from bamboo pulp and expanded graphene (EG) using a grinder. This strategy is scalable and environmentally friendly for high-efficiency exfoliation and dispersion of graphene in an aqueous medium. The in situ-generated CNFs play a key role in this process, acting as a "green" dispersant. Next, the obtained CNFs-FLG is used as a functional filler in a polyoxyethylene (PEO) matrix. When the composition of CNFs-FLG is 50 wt.%, the resultant PEO/CNFs-FLG nanocomposite film exhibits a Young's modulus of 1.8 GPa and a tensile strength of 25.7 MPa, showing 480% and 260% enhancement as compared to those of the pure PEO film, respectively. Remarkably, the incorporation of CNFs-FLG also provides the nanocomposite films with a stunning electrical conductivity (72.6 S/m). These attractive features make PEO/CNFs-FLG nanocomposite films a promising candidate for future electronic devices.

Sensitivity Enhanced Plasmonic Biosensor Using Bi2Se3-Graphene Heterostructures: A Theoretical Analysis.

This study provided a theoretical insight for designing novel plasmonic biosensors using bismuth selenide (Bi2Se3)-Graphene heterostructures. It was a van der Waals (vdWs) stacked configuration composed of gold (Au) film, few quintuple layer (QL) Bi2Se3 and few-layered graphene. In particular, the proposed biosensor was created by Goos-Hänchen (GH) shift rather than phase, resulting in a more sensitive biosensing response. Under the excitation of 632.8 nm, significant sensitivity enhancement performance was obtained via varying the thickness of Bi2Se3-Graphene heterostructures. The best configuration was 32 nm Au film-2-QL Bi2Se3-3-layer graphene, generating the largest GH shift, as high as -1.0202 × 104 µm. Moreover, the highest detection sensitivity was determined to be 8.5017 × 106 µm/RIU, responding to a tiny refractive index (RI) change of 0.0012 RIU (RIU, refractive index unit). More importantly, our proposed biosensor has shown a theoretical feasibility of monitoring virus samples. For example, there was an efficient linear detection range for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2, 0~13.44 nanomole (nM)) and its Spike (S) glycoprotein (0~59.74 nM), respectively. It is expected that our proposed plasmonic biosensor has a potential application in performing sensitive detection of SARS-CoV-2.

Few-Layer Graphene as an Efficient Buffer for GaN/AlN Epitaxy on a SiO2/Si Substrate: A Joint Experimental and Theoret-ical Study

Single-layer (SLG)/few-layer (FLG) and multilayer graphene (MLG) (&gt;15 layers) samples were obtained using the CVD method on high-textured Cu foil catalysts. In turn, plasma-assisted molecular beam epitaxy was applied to carry out the GaN graphene-assisted growth. A thin AlN layer was used at the initial stage to promote the nucleation process. The effect of graphene defectiveness and thickness on the quality of the GaN epilayers was studied. The bilayer graphene showed the lowest strain and provided optimal conditions for the growth of GaN/AlN. Theoretical studies based on the density functional theory have shown that the energy of interaction between graphene and AlN is almost the same as between graphite sheets (194 mJ/m2). However, the presence of vacancies and other defects as well as compression-induced ripples and nitrogen doping leads to a significant change in this energy.

Elemental carbon and hydrogen concentrations as the main factors in gas-phase graphene synthesis: Quantitative fourier-transform infrared spectroscopy study

Gas-phase microwave plasma-assisted synthesis of freestanding graphene is a promising route to produce high-quality graphene flakes. However, a comprehensive understanding of the gas-phase kinetics that is required to advance production rates and yields is still lacking. Here, we use line-of-sight Fourier-transform infrared (FTIR) absorption spectroscopy as an in situ diagnostic to measure gaseous species formed during graphene synthesis, thereby elucidating the chemical kinetics mechanism. Different carbonaceous precursors that lead to the formation of either few-layer graphene flakes or soot-like particles are examined, and the results are compared with numerical simulations and mass spectrometry measurements. Quantitative FTIR measurements show a correlation between concentration of atomic carbon and hydrogen in the post-plasma region and particle morphology. Lower carbon and higher hydrogen concentrations lead to graphene formation, while higher carbon and lower hydrogen concentrations shift the reaction toward soot-like particles. We also investigate how the precursor chemical composition, precursor flowrate, and delivered microwave power affect the carbon concentration in the post-plasma region, thus enabling to control particle morphology.

Competitive growth between the top and bottom layers of few-layer graphene at the domain boundary merging stage

Compared with monolayer graphene, few-layer graphene (FLG) also has a broader application prospect in the fields of composite materials, conductive coatings, metal corrosion prevention and electronic devices requiring tunable electronic structures. Herein, FLG is grown on Cu foil by chemical vapor deposition (CVD) and the merging of graphene domain boundary (GDB) network is directly observed by optical microscope (OM). Raman spectra and energy dispersive spectroscopy (EDS) results show that the defect degree of graphene at GDBs is lower than that at domain interior. Raman mapping results indicate that the structure of FLG grown at 980 °C is inhomogeneous and there exist a terraced structure at the GDBs. The atomic force microscopy (AFM) results show that the FLG grown at 980 °C has about ∼7 layers at the GDBs and ∼13 layers at domain interior, respectively. In addition, the Raman spectra results also disclose an unusual phenomenon that graphene at GDBs grown at 980 °C has lower ID/IG ratios than that grown at 1000 °C. A competitive growth mechanism of the top and bottom layers of FLG is proposed to shed light on the synergistic effect of catalysis of Cu and temperature on the late growth stage of FLG.

SiO–Sn2Fe@C composites with uniformly distributed Sn2Fe nanoparticles as fast-charging anodes for lithium-ion batteries

SiO-based materials represent a promising class of anodes for lithium-ion batteries (LIBs), with a high theoretical capacity and appropriate and safe Li-insertion potential. However, SiO experiences a large volume change during the electrochemical reaction, low Li diffusivity, and low electron conductivity, resulting in degradation and low rate capability for LIBs. Here, we report on the rapid crafting of SiO–Sn2Fe@C composites via a one-step plasma milling process, leading to an alloy of Sn and Fe and in turn refining SiO and Sn2Fe into nanoparticles that are well dispersed in a nanosized, few-layer graphene matrix. The Sn and Fe nanoparticles generated during the first Li-insertion process form a stable network to improve Li diffusivity and electron conductivity. As an anode material, the SiO–Sn2Fe@C composite manifests high reversible capacities, superior cycling stability, and excellent rate capability. The capacity retention is found to be as high as 95% and 84% at the 100th and 300th cycles under 0.3 ​C. During rate capability testing at 3, 6, and 11 ​C, the capacity retentions are 71%, 60%, and 50%, respectively. This study highlights that this simple, one-step plasma milling strategy can further improve SiO-based anode materials for high-performance LIBs.

Mechanical exfoliation assisted with carbon nanospheres to prepare a few-layer graphene for flexible strain sensor

Graphene is an ideal material for the preparation of wearable flexible sensors because of its excellent electrical and mechanical properties. However, the preparation of effective graphene is still challenging due to factors such as the low efficiency of the final product, complex processes, environmental pollution, etc. In this study, a method of exfoliating graphite into graphene using water as solvent and carbon nanospheres as exfoliation agents under a high shear rate of microfluidic homogenizer is proposed. The prepared graphene can be used for the preparation of flexible strain sensors by screen printing. The number of layers of the prepared graphene was 2–5 layers. Meanwhile, the sensor had excellent flexibility, which still maintains a stable working state after 100,000 times of flexing test or 1,000 times of abrasion test, and can be used as a wearable flexible strain sensor to monitor the relative change of resistance caused by the movement of the limbs. This method is of great value for the green preparation of graphene and provides a possibility for high-quality and batch production of flexible strain sensors.

Study on the mechanically exfoliated graphene saturable absorption dependence on the number of layers and its influence on passive mode-locking erbium-doped fiber laser dynamics

We experimentally investigated the saturable absorption influence of graphene layers with natural stacking order in an erbium-doped fiber laser passive mode-locking. Mechanically exfoliated graphene saturable absorber (MEGSA) samples, ranging from 1 to 6 layers, were fabricated preserving their natural ABA stacking order and precisely characterized by 2D band profile from Raman spectroscopy. By incorporating the samples as saturable absorbers (SA) in the fiber laser, mode-locking performances with pulse duration from 670–780 fs and bandwidth from 3.8–4.6 nm could be generated. Also, we identified a transition in the mode-locking activation mechanism from non-self-starting, for monolayer and bilayer graphene, to self-starting, for trilayer and few-layer graphene, which is a strong indicative of fast-to-slow saturable absorption response dependence on the number of graphene layers.