Number Of Graphene Layers Research Articles

Unsupervised learning of spatially-resolved ARPES spectra for epitaxially grown graphene via non-negative matrix factorization

This study proposed an unsupervised machine-learning approach for analyzing spatially-resolved ARPES. A combination of non-negative matrix factorization (NMF) and k-means clustering was applied to spatially-resolved ARPES spectra of the graphene epitaxially grown on a SiC substrate. The Dirac cones of graphene were decomposed and reproduced fairly well using NMF. The base and activation matrices obtained from the NMF results reflected the detailed spectral features derived from the number of graphene layers and growth directions. The spatial distribution of graphene thickness on the substrate was clearly visualized by the clustering using the activation matrices acquired via NMF. Integration with k-means clustering enables clear visualization of spatial variations. Our method efficiently handles large datasets, extracting spectral features without manual inspection. It offers broad applicability beyond graphene studies to analyze ARPES spectra in various materials.

Observation of novel carbon nanocorals during the synthesis of graphene and investigations on their composition, morphological and structural properties

Novel carbon nanocorals (CNCs) are observed during the synthesis of graphene on copper substrates by thermal chemical vapor deposition, using precursor gas acetylene (C2H2) and carrier gas argon (Ar). CNCs have unique structure and investigations are carried out on structural and elemental compositions by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray excited Auger electron spectroscopy (XAES), energy dispersive X-ray spectroscopy (EDS), field emission scanning electron microscopy (FESEM), and high resolution transmission electron microscopy (HRTEM). The graphitic nature of the CNCs is evident from characteristic D, G, and 2D bands obtained from Raman spectrum. Elemental composition analysis by XPS shows presence of sp2 and sp3 hybridized carbon whereas XAES quantifies percentage of sp2 and sp3 hybridized carbon. FESEM micrographs show a uniform distribution of densely packed CNCs throughout the sample, and formation of groups of CNCs with distinct contours on the surface. The cross-sectional FESEM shows stacking of large number of graphene layers with dendrites. HRTEM analysis further supports observations of FESEM and elaborates structural morphology of the CNCs. Synthesis, characterization and analysis of the properties of carbon nanocorals are reported here, for the first time.

Observation of thickness-independent ultrafast relaxation times in MPCVD few-layer graphene

Graphene presents unique optoelectronic properties, making it attractive for the development of a wide range of new and advanced technological applications such as high-speed photodetectors and all-optical modulators. The study and control of the generated carriers in graphene, namely their ultrafast relaxation dynamics, are of great importance for these applications. Here, we report the ultrafast relaxation times of photogenerated carriers in few-layer graphene grown by microwave plasma chemical vapour deposition. Graphene samples with 3, 5 and 6 layers were studied by degenerate femtosecond optical pump-probe spectroscopy. We observed a fast relaxation constant on the order of 120−180fs and a slow relaxation constant below 1 ps, associated with carrier-carrier scattering and carrier-phonon scattering processes, respectively. These results suggest that small variations in the number of graphene layers do not affect the dynamics.

Liquid-phase shear exfoliation of graphite and its application as corrosion protection coating on aluminum substrate

Although aluminum (Al) or its alloys are moderately protected by a native oxide layer, the presence of chloride ions in aqueous media in direct contact causes pitting attacks and accelerates corrosion. Using graphene as a coating protector can obstruct corrosion due to its numerous chemical and physical properties. This study investigates corrosion protection of Al using graphene nanosheets (GNSs) produced by liquid phase shear exfoliation method (LPE). To do so, few layer-thick graphene nanosheet colloidal solutions were produced by a scalable eco-friendlier lower cost approach. The GNSs were thoroughly characterized using complementary characterization techniques to determine its quality. Spectroscopic and microscopic analyses indicate the synthesis of few-layers graphene (≤ 5 layers) with a high quality. Once approved, the colloidal solution of GNSs was spread over Al substrate by spray coating method, widely used in industrial manufacturing. Raman and near infrared spectroscopies, X-ray diffraction, microscopy techniques including scanning electron, transmission electron and atomic force microscopies were used to investigate morphological and structural behavior of coated GNSs films either on glass or Al substrates. Density functional theory (DFT) calculations revealed the interaction between the two materials is of the physisorption type, with almost no charge transfer and almost no effect of the number of graphene layers. Electrochemical measurements enabled to investigate the corrosion resistance of GNSs films and its stability over time in a 0.5 M sodium chloride (NaCl) solution, similar to marine surroundings. It was found that introducing a GNSs film can indeed reduce the corrosion rate and preserve Al substrate for an extended period.

Electrical conductivity of graphene/copper composites at lattice scale

Graphene/copper composites are potential structure-function integrated materials. Different from previous micro-nano scale composites, graphene/copper lattice-scale composites and their effects on electrical conductivity are investigated in this work. Using the first-principles calculation to explore the effects of different numbers of graphene layers on the properties of graphene/copper composites, it is found that with the increase of graphene layer numbers, the interfacial bonding strength improves, but the electrical properties show a decreasing trend due to the electron scattering and increasing Cu–C layer distance. The single-layer graphene/copper composite has the most excellent electrical properties, with the highest density of states at the Fermi level and the most charge transfer. A series of layered-structural composites at lattice scale are screened, and their electrical properties and dynamic stability are also predicted. These composites rely on metallic bonding to connect copper and carbon atoms, most of which show obvious vertical charge transfer and high conductivity, with short Cu–C layer distance and alternating arrangement of metal layers and hexagonal carbon atoms. CuC2 (derived from MgB2) has the highest average conductivity and dynamic stability and can be considered an ideal lattice-scale composite. The development of new lattice-scale composites is significant for the future research of graphene/copper composites.

Interfacial heat transport properties of graphene/natural rubber composites studied based on molecular dynamics approach

The interface between graphene and natural rubber significantly impacts the thermal properties of graphene/natural rubber composites. This paper uses molecular dynamics to investigate interfacial heat transport. The study found that the thermal conductivity of the composites increases non-linearly with graphene content: a 136 % increase at 10.5 % graphene and only 12.23 % at 16.4 % graphene. As graphene content increases, graphene agglomerates within the natural rubber due to weak van der Waals forces. The interfacial thermal resistance of the composites increases with temperature, rising by 69.94 % from 200K to 450K. When pressure increases from 0.1 MPa to 2.5 MPa, the maximum change in interfacial thermal resistance is 24.39 %. The study also found that interfacial thermal resistance increases with the number of graphene layers. Thus, the interfacial thermal resistance between graphene and natural rubber is the main reason for the minor change in the thermal conductivity of the composites, with temperature having a greater impact.

Beyond lithium-ion batteries: Are effective electrodes possible for alkaline and other alkali elements? Exploring ion intercalation in surface-modified few-layer graphene and examining layer quantity and stages

In the pursuit of reliable energy storage solutions, the significance of engineering electrodes cannot be overstated. Previous research has explored the use of surface modifiers (SMs), such as single-side fluorinated graphene, to enhance the thermodynamic stability of ion intercalation when applied atop few-layer graphene (FLG). As we seek alternatives to lithium-ion batteries (LIBs), earth-abundant elements like sodium and potassium have emerged as promising candidates. However, a comprehensive investigation into staging intercalation has been lacking thus far. By delving into staging assemblies, we have uncovered a previously unknown intercalation site that offers the most energetically favorable binding. Here, we study the first three elements in both alkali (Li, Na, K) and alkaline (Be, Mg, Ca) earth metals. Furthermore, the precise mechanism underlying this intercalation system has remained elusive in prior studies. In our work, we employed density functional theory calculations with advanced hybrid functionals to determine the electrical properties at various stages of intercalation. This approach has been proven to yield more accurate and reliable electrical information. Through the analysis of projecting density of states and Mulliken population, we have gained valuable insights into the intricate interactions among the SM, ions, and FLG as the ions progressively insert into the structures. Notably, we expanded our investigation beyond lithium and explored the effectiveness of the SM on ions with varying radii and valence, encompassing six alkali and alkaline earth metals. Additionally, we discovered that the number of graphene layers significantly influences the binding energy. Our findings present groundbreaking concepts for material design, offering diverse and economically viable alternatives to LIBs. Furthermore, they serve as a valuable reference for fine-tuning electrical properties through staging intercalation and the application of SMs.

Few-layered-graphene - Si3N4 composite powders prepared by decomposition of methane onto a Si3N4 powder bed: Control of the average number of layers in the graphene stack

The chemical vapor deposition of carbon is performed onto a commercial silicon nitride powder bed. This produces few-layered-graphene (FLG) films or islands on the Si3N4 particles. The samples are characterized by several techniques including Raman spectroscopy, scanning and transmission electron microscopy. The experimental parameters of the methane (CH4) decomposition (temperature, CH4 concentration, dwell time) are correlated to the average number of graphene layers (N). Complete coverage of the Si3N4 particles is achieved for FLG with N controlled in the range 5–12, corresponding to 4–12 wt%. of carbon. Below that, for stacks with N = 3–4, the coverage of the surface by FLG islands is not total. The value found for the activation energy of CH4 conversion into carbon shows that island-growth is favored over layer-growth. A macroscopical method based on a carbon proportion evaluation gives an approximation of both the coverage ratio and the average number of layers in the stack.

The Tunable Parameters of Graphene-Based Biosensors.

Graphene-based surface plasmon resonance (SPR) biosensors have emerged as a promising technology for the highly sensitive and accurate detection of biomolecules. This study presents a comprehensive theoretical analysis of graphene-based SPR biosensors, focusing on configurations with single and bimetallic metallic layers. In this study, we investigated the impact of various metallic substrates, including gold and silver, and the number of graphene layers on key performance metrics: sensitivity of detection, detection accuracy, and quality factor. Our findings reveal that configurations with graphene first supported on gold exhibit superior performance, with sensitivity of detection enhancements up to 30% for ten graphene layers. In contrast, silver-supported configurations, while demonstrating high sensitivity, face challenges in maintaining detection accuracy. Additionally, reducing the thickness of metallic layers by 30% optimizes light coupling and enhances sensor performance. These insights highlight the significant potential of graphene-based SPR biosensors in achieving high sensitivity of detection and reliability, paving the way for their application in diverse biosensing technologies. Our findings pretend to motivate future research focusing on optimizing metallic layer thickness, improving the stability of silver-supported configurations, and experimentally validating the theoretical findings to further advance the development of high-performance SPR biosensors.

Effects of quenching rate on the plasma gas-phase synthesis of graphene: Insight from the experiments and ReaxFF studies

This investigation analysed the effects of quenching rate on the plasma gas-phase synthesis of graphene. The quenching rate was modulated by the flowrate/type of radial gas whish was injected in the plasma downstream. The experimental results showed that the plasma pyrolysis of acetylene produced spherical carbon nanoparticles. The content graphene flakes in the products increased with the quenching effect, and the layer number of graphene decreased accordingly. Further characterisation confirmed that a high quenching rate increased the crystallinity of the product, reduced the amorphous carbon content, and resulted in better oxidation resistance. The graphene formation pathway was carried out by the molecular dynamics simulations (ReaxFF), focusing on the effect of the quenching rate on graphene growth. As the quenching rate increased, the decrease in the time for surface reactions lowered the generation of five- and seven-membered rings, reducing the possibility of edge growth bending. Besides, an increased quenching rate rapidly lowered the growth temperature and thus retarded the C–H bond breakage at the edges of the carbon clusters. The C–H bonds terminated C–C bond formation at the edges of the carbon clusters, preventing edge growth bending of the carbon clusters, and thus contributing to the growth of lamellar structure. These results suggested that increasing the quenching rate is an effective method for regulating the plasma gas-phase synthesis of graphene.

Influence of heat transfer at the graphene–polyimide interface on laser-induced graphene formation

Laser-induced graphene (LIG) provides a three-dimensional porous structure of graphene, which is suitable for application to energy storage devices and flexible electronics. Controlling the morphology and structure of LIG and understanding its underlying principle are important for enhancing the performance of LIG-based devices. Here, we investigated the effects of graphene interfacing with a precursor material on the LIG formation. A CO2 laser with different powers and scan rates was irradiated on a polyimide film covered with mono-, bi-, and trilayer graphene to fabricate in situ LIG contacts. As the number of graphene layers increases, the threshold energy required for the LIG formation decreases. In addition, the interfacing graphene causes spreading and smoothing of the LIG electrodes in the in-plane direction. A numerical study on the effect of the interfacing graphene on heat transfer was also conducted. The simulation results showed that the graphene layer enhances thermal diffusion to facilitate the LIG formation; this was also observed in the experimental results. Our study on the interfacial effects of a nanomaterial on the LIG formation provides design guidelines for considering heat transfer in LIG electronics fabricated with heterogeneous materials and structures.

Investigation of thermal conductivity and mechanical properties in multi-layer of graphene and graphene oxide: a molecular dynamics study

ABSTRACT Multi-layered graphene and graphene oxide have been used as reinforcements in nanodevices and nanocomposites due to their extraordinary mechanical and thermal properties. However, compared to graphene, graphene oxide has a lower Young’s modulus and lower thermal conductivity. Nanodevices and nanocomposites based on multi-layered graphene and graphene oxide require different mechanical properties and thermal conductivity. This study employed molecular dynamics simulation to investigate 10 models of multi-layered graphene and graphene oxide (in the form of different layer arrangements) in single, double, and triple layers. The results showed that an increase in the number of graphene oxide layers leads to irregularities in the nanosheets, resulting in decreased thermal conductivity (by 64.4%) of the nanosheets decreases. Furthermore, the greater number of graphene layers in multi-layer nanosheets resulted in an increase in Young’s modulus (by 79.3%) and tensile strength (by 73.7%). Moreover, the arrangement of graphene and graphene oxide is a crucial factor that can significantly impact the mechanical properties and thermal conductivity of the models. Moreover, an increase in temperature can lead to a decrease in Young’s modulus of multilayered nanosheets. Increasing the number and size of graphene layers enhances both the ultimate tensile strength and the critical energy release rate.

Optical image analysis for graphene layer detection: Enhanced green channel methodology

Graphene, a material of increasing research interest, requires accurate layer identification due to its sensitivity to layer count. Existing methods for graphene layer number identification are either time-consuming or of low accuracy, with high-accuracy methods often requiring expensive processes. This paper aims to address this challenge by proposing a cost-effective and efficient approach. Specifically, the current work highlights only the green channel—one of the three primary color channels (red, green, blue) that make up an optical image—from images of exfoliated graphene flakes for layer count identification. A linear regression is performed between pixel position and substrate green channel value, and this effect is subtracted from the entire optical image to mitigate background effects. By storing the range of green channel values for each type of flake (monolayer, bilayer, or tri-layer) based on a few images, we establish thresholds for identifying different types of layers in a particular setup. Additionally, our methodology allows for flexible threshold tuning using a single reference image, enabling adjustment to changes in detection setup such as illumination level, magnification, or microscope used. Demonstrating high accuracy and flexibility, this methodology presents a suitable technique for graphene layer number identification without the need for large datasets or expensive instruments.

Coal-based graphene formation by CO2 laser scribing: Various structures and excellent electrochemical performance

The laser-induced technique is a cost-effective and environmentally-friendly method for upgrading coal into high value-added graphene materials. Here, laser-induced graphenes (LIGs) were prepared from different rank coals in one-step under vacuum conditions using a designed CO2 infrared laser device. The characteristics of laser-induced products were studied by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. The electrochemical characteristics of coal-based laser-induced graphenes (C-LIGs) were examined in a three-electrode test system. Results show that subbituminous coal, bituminous coal, and low-metamorphic anthracite can form LIG with fewer layers after laser irradiation. The morphology of C-LIG is a layered porous structure. Corrugated folds can be observed at the edges of the C-LIG layer. There are only a few layers of graphene, with the majority of them concentrated in 2–10 layers. The most interesting result is that LIG prepared from low volatile bituminous coal has the highest crystallinity, the largest aromatic layer size, and the lowest average graphene layer number. Furthermore, LIG made from low volatile bituminous coal (LIG-ZJ) exhibits excellent electrical double-layer capacitive behavior, low equivalent series resistance (3.73 Ω), good rate capability, excellent cycling stability, greater Coulombic efficiency, and high mass specific capacitance. The LIG-ZJ electrode exhibits a high specific capacitance of 1879.92 F/g at 1 A/g, which is nearly ten times greater than that of most activated carbon electrodes reported. In addition, its power density and energy density can reach up to 924.07 kW/kg and 217.11 Wh/kg. These results indicate that coal-based laser-induced graphene has significant potential for application in the field of electrochemical energy storage.

Terahertz absorption properties of different graphene layers based on the Salisbury effect

Terahertz (THz) absorbers based on the Salisbury screen have attracted significant attention for high absorption performance and simple structure. Graphene is suitable for high-performance THz absorbers due to its extraordinary electronic and optical properties. The study of graphene THz absorbers based on Salisbury screens has attracted great interest, where the number of graphene layers significantly affects the interface impedance matching and absorption efficiency. In this work, we proposed a sandwich-structured graphene/Polyimide (PI) /Au THz absorber based on the Salisbury screen. The results show that the absorption peak tended to increase and then decrease with the increase in the number of graphene layers. The simulation demonstrates that the real and imaginary parts of the relative impedance of the 3-5 layer graphene absorber were 1.02 and 0.01, which achieved a better impedance matching with the free space. Meanwhile, the measured sheet resistance value of 426 Ω/sq was closest to the free-space impedance value of 377 Ω, consistent with the simulation results. The corresponding absorption reached a maximum value of 98.7% at 0.82 THz (measured). In addition, the absorption peak decreased from 98.7% to 86.7% as the angle of incidence increased from 0° to 60°. This demonstrates the advantage of wide-angle absorption. The proposed device is suitable for applications in electromagnetic shielding and imaging, while the suggested method can be employed for the fabrication of other graphene-based devices.

Observation of the early stages of environmental contamination in graphene by friction force.

Exposure to ambient air contaminates the surface of graphene sheets. Contamination may arise from different sources, and its nature alters the frictional behavior of the material. These changes in friction enable the observation of the early stages of contaminants' adsorption in graphene. Using a friction force microscope, we show that molecular adsorption initiates at the edges and mechanical defects in the monolayer. Once the monolayer is covered, the contaminants spread over the additional graphene layers. With this method, we estimate the contamination kinetics. In monolayer graphene, the surface area covered with adsorbed molecules increases with time of air exposure at a rate of 10-14m2/s, while in bilayer graphene, it is one order of magnitude smaller. Finally, as the contaminants cover the additional graphene layers, friction no longer has a difference concerning the number of graphene layers.

Unveiling the magic of twist angle: Thermal transport in Two-dimensional Graphene/MoS2/Graphene Heterostructures

Thermal transport properties of two-dimensional vdW heterostructures have attracted considerable research interests in electron-related devices due to their powerful capability of multi-functional integration. Herein, we investigated the in-plane and out-of-plane thermal conductivity of graphene/MoS2 heterostructures under various twist angles utilizing molecular dynamics simulations. It was found that the in-plane thermal conductivity of MoS2 layer in heterostructures decreases with twist angle. Notably, the lowest thermal conductivity occurs at a twist angle of 10.893°, just 47.3 % of that in untwisted MoS2 layers in heterostructure. In addition, the interlayer interfacial thermal resistance between graphene and MoS2 layer increases with the twist angle but decreases with the layer numbers of graphene. The atomic position deviation, potential energy surface, phonon state of density are calculated to reveal the regulation mechanism of thermal conductivity by twist angle. Interestingly, it is found that the twist angles and the layer numbers of graphene can control the atomic vibration arising from potential energy surfaces and phonon transport through the overlap of phonon density of states between graphene and MoS2 layers. This study can provide valuable insights into the thermal conductivity modulation and phonon transport mechanism of heterostructures.

Effects of the Number of Graphene Layers and Graphene Diaphragm Size on High Frequency Electrostatic Speakers

Effects of the Number of Graphene Layers and Graphene Diaphragm Size on High Frequency Electrostatic Speakers

Photonic quasi-crystal fiber electro-optical modulator

The integration of graphene with optical fiber is considered to be a new interdisciplinary research hotspot for functional fiber. In this paper, an electro-optical modulator based on a six-fold Stampfli-type photonic quasi-crystal fiber (PQF) is theoretically proposed with a sandwiched graphene/hexagonal boron nitride/graphene (Gr/hBN/Gr) film covering all the hole walls. This design exhibits a strong light-graphene interaction with an excellent modulation depth of ∼64 dB mm−1 at 1550 nm by applying an external bias voltage (below 30 V) on both graphene layers. As the Fermi level of the graphene changes with voltage, the fiber shows ‘On’ and ‘Off’ states, serving well as a light-switch. For the modulator performance, the dependence of modulation depth on multiple factors is studied in terms of the layer numbers of graphene and hBN films, the incident wavelength, and the structure parameters. Interestingly, an attenuation peak occurs due to the epsilon-near-zero effect in graphene and shows a linear relationship between the wavelength and the Fermi level. This design provides a guidance for the integration of PQF and graphene, and holds great promise for future all-fiber systems.

Optical spatial differentiation enabled layer sensing of two-dimensional atomic crystals

Zero-thickness model and slab model are two important models in the description of optical behaviors in two-dimensional atomic crystals. The predicted difference in optical behaviors between the two models is very small, which is difficult to distinguish by established measurement methods. Here, we present an optical spatial differentiation method to examine the difference in edge images of different graphene layers. The theoretical results show that the edge imaging is significantly different between the two different models. When the beam reflection is at the Brewster angle, different graphene layers are used to adjust the spatial differentiation. It is shown that the slab model is more sensitive to the number of graphene layers. The zero-thickness model is more suitable for one-dimensional optical differential operation. Moreover, the spatial differentiation plays the role of a band-pass filter. The high-frequency edge information components will pass through the filter, thus realizing layer-sensitive edge-enhanced imaging. In addition, we do not focus on the verification of the exact model, but only provide an alternative method to characterize the number of graphene layers based on two models, and also provide possibilities for achieving imaging edge detection by graphene differential operators. This study may provide a possible method for the optical characterization of two-dimensional atomic crystals.