High-quality Graphene Research Articles

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

8-Inch Wafer Scale, Transfer-Free, High-Quality Monolayer Graphene Growth on Ti-Buffered Si (001) Substrates At 100 ºC via Plasma-Assisted Chemical Vapor Deposition

CVD graphene with high electrical conductivity: empowering applications

Abstract Graphene is an extraordinary material boasting a unique structure, enthralling properties, and promising application vistas. Particularly, the remarkable electrical conductivity of graphene confers it with an inimitable superiority in multiple fields. Endeavors have been continuously made to progressively elevate the conductivity of graphene materials that are synthesized using chemical vapor deposition (CVD), the primary means to prepare high-quality graphene in batches. From this perspective, we offer a comprehensive analysis and discussions on the growth, transfer, and post-treatment strategies evolved towards highly conductive graphene over the past five years. Large-area graphene films, ranging from monolayer to multilayer ones, are initially addressed, succeeded by graphene-based composites which enable traditional metals and non-metal materials to showcase novel or enhanced electrical performances. Eventually, an outlook for future directions to achieve higher electrical conductivity and to develop novel applications for CVD graphene materials is provided.

Growth Kinetics of Graphene on Cu(111) Foils from Methane, Ethyne, Ethylene, and Ethane.

Chemical vapor deposition of carbon precursors on Cu-based substrates at temperatures exceeding 1000 °C is currently a typical route for the scalable synthesis of large-area high-quality single-layer graphene (SLG) films. Using molecules with higher activities than CH4 may afford lower growth temperatures that might yield fold- and wrinkle-free graphene. The kinetics of growth of graphene using hydrocarbons other than CH4 are of interest to the scientific and industrial communities. We measured the growth rates of graphene islands on Cu(111) foils by using C2H2, C2H4, C2H6 and CH4, respectively (each mixed with H2). From such kinetics data we obtain the activation enthalpy (ΔH≠) of graphene growth as shown in parentheses (C2H2 (0.93±0.09 eV); C2H4 (2.05±0.19 eV); C2H6 (2.50±0.11 eV); CH4 (4.59±0.26 eV)); C2Hy (y=2, 4, 6) show similar growth behavior but CH4 is different. Computational fluid dynamics and density functional theory simulations suggest that C2Hy differs from CH4 due to different values of adsorption energy and the lifetime of relevant carbon precursors on the Cu(111) surface. Combining experimental and simulation results, we find that the rate determining step (RDS) is the dissociation of the first C-H bond of CH4 molecules in the gas phase, while the RDS using C2Hy is the first dehydrogenation of adsorbed C2Hy that happens with assistance of H atoms adsorbed on the Cu(111) surface. By using C2H2 as the carbon precursor, high-quality single-crystal adlayer-free SLG films are achieved on Cu(111) foils at 900 °C.

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Scalable and High-Quality Monolayer Graphene Transfer onto Polymer Membranes Assisted by Camphor

Procedure for Fabrication and Characterization of Van-der-Waals Heterostructures

In this work we provide a step-by-step description of the technique for manufacturing various van der Waals heterostructures. First, we discuss the procedure to obtain monolayer and few-layer flakes from layered materials, in particular from graphite and hexagonal boron nitride. Next, we consider different approaches to the assembly depending on the required final device. Further, we describe in detail the procedure for making ohmic contacts and give the parameters for plasma chemistry and metal deposition. We observe the field effect in transport measurements but a number of features – a strong shift of the charge neutral point from the zero-gate voltage, a large resistance away from the charge neutral point, and low mobility – indicate a problem with the quality of the resulting devices. Nevertheless, one of the fabricated devices demonstrates reasonable quality – the maximum mobility is estimated at 15000 cm2V–1s–1, the magnetic field dependences demonstrate the quantum Hall effect, which is standard for high-quality graphene. Unexpectedly, scanning electron microscope images of the resulting devices reveal a large amount of contamination on the surface of the flakes, which may explain the corresponding quality of our devices. Preliminary results of flakes cleaning with chemical compounds and thermal treatment are given.

Advancing Graphene Imaging for Clear Identification of Lattice Defects: The Application of Revolve Sphere Levelling to Scanning Tunnelling Microscopy Images.

Application of revolve sphere levelling (RSL) as a practical and effective image processing tool for enhancing scanning tunnelling microscopy (STM) images of graphene atomic lattices is presented. Low-cost, ambient, and non-invasive STM methods overcome limitations of traditional imaging methods like scanning transmission electron microscopy (STEM) and transmission electron microscopy (TEM) that can introduce or alter defects in graphene. Utilizing high-quality graphene synthesized via Paragraf's patented Metal-Organic Chemical Vapor Deposition (MOCVD) method, RSL, which is easily implemented via the Gwyddion software package, effectively highlights the hexagonal lattice structure and specific defect structures. This provides clarity of the atomic structure that traditional methods struggle to achieve. This research emphasizes the utility of RSL in materials science for defect identification in graphene, and points to future research in optimizing RSL for a broader range of defects and applications in other 2D materials.

Preparation and growth mechanism of high-quality multilayer graphene from simulated coal pyrolysis gas via chemical vapor deposition

Chemical vapor deposition (CVD) of graphene from coal pyrolysis gas provides new ways for both large-scale graphene preparation and high value-added utilization of coal. However, green, efficient and continuous preparation of high-quality multilayer graphene with both good uniformity and ideal structure characteristic remains a great challenge. Herein, we first investigated the influence of main carbonaceous species (CH4, C2H6, C3H8, CO2, and CO) in coal pyrolysis gas on the quality of CVD graphene products. The experimental results indicated that CO2 and CO have little effect on the growth of graphene, while methane as carbon source is conducive to obtain ideal graphene materials, propane and ethane could also influence structural defects and layer number of graphene products remarkably. On this basis, we designed a mixed gas of methane, ethane, and propane with optimized ratio as simulated coal pyrolysis gas, and successfully prepared high-quality multilayer graphene products on nickel foam from the as-designed simulated coal pyrolysis gas by CVD method. Notably, with a CH4:C2H6:C3H8 ratio of 2:1:1, the graphene products prepared from simulated coal pyrolysis gas outperformed that of raw coal pyrolysis gas in terms of physical structure, layer number, and quality uniformity. The corresponding I2D/IG value reached 0.97. The graphene growth process and mechanism were investigated and discussed macroscopically and microscopically. This work is of great significance for the intrinsic understanding of CVD growth of graphene from coal pyrolysis gas, and also inspires an efficient and environmentally friendly avenue for high-throughput, uniform production of high-quality graphene materials.

Electrochemical exfoliation of graphene nanosheets and development of a novel efficient Ni-CeO2-Gr ternary nanocomposite coatings for dual functional anti-corrosion and wear-resistance

Nickel-based coatings offer excellent corrosion, wear resistance, and mechanical strength, and can be further improved with additives, making them ideal for harsh environments like marine and chemical industries. In the present study, graphene (Gr) nanosheets were synthesized via electrochemical exfoliation and a novel Ni-CeO2-Gr nanocomposite coating was prepared by an electrochemical co-electrodeposition technique on a Cu substrate in a traditional Watts bath. The coatings (pure Ni, Ni-Gr, Ni-CeO2 and the ternary Ni-CeO2-Gr) were characterized using optical microscopy, scanning electron microscopy (SEM) coupled with energy-dispersive spectrometry (EDS), X-ray diffraction (XRD), Raman spectroscopy, Vickers microhardness and micro-scratch tests. The electrochemical properties of the coatings were evaluated by electrochemical impedance (EIS) and DC-polarization measurements in 0.5 M NaCl. SEM-EDS, Raman, and XRD analysis confirmed the successful synthesis of high-quality graphene and the incorporation of CeO2 nanoparticles and graphene nanosheets into the nickel coating matrix. It was found that the ternary Ni-CeO2-Gr coating exhibited a high microhardness (915.6 HV), improved cohesive strength and enhanced corrosion resistance (544 KΩ.cm−2) compared to pure Ni coatings (30 KΩ.cm−2) due to the synergistic effect of the graphene and CeO2 duplex layer within the Ni matrix, forming a robust anticorrosion barrier. These findings offer valuable insights into the designing highly efficient materials for corrosion protection.

High-value multilayer graphene oxide prepared by catalytic pyrolysis of petroleum tar and applications: Trash to treasure

Petroleum tar (PT), a by-product of heavy oil refining, poses significant environmental challenges due to its high production volume and associated pollution risks. This study presents an innovative approach for the catalytic conversion of PT into multilayer graphene oxide using nickel foam (NiF) as a catalyst at reaction temperatures of 500 °C and 700 °C (GT/Ni500 and GT/Ni700). The process effectively decomposes PT and facilitates the structured rearrangement of carbon atoms into graphene layers. Comprehensive characterization techniques, including SEM-EDS, HRTEM, BET, XRD, XPS, and Raman spectroscopy, confirm the formation of high-quality graphene oxide. The synthesized GT/Ni700 material exhibits remarkable electrochemical performance with a specific capacitance of 3.34F/g. GT/Ni500 shows adsorption capacities of 59.86 mg/g for Pb2+ and 56.84 mg/g for Cu2+. Life Cycle Assessment reveals a substantial reduction in the carbon footprint, with CO2 equivalents for GT/Ni500 and GT/Ni700significantly lower than traditional methods, at 17.64 kg/CO2eq and 14.03 kg/CO2eq, respectively, representing a reduction of over 50 %. This study not only offers a sustainable pathway for PT utilization but also provides advanced materials with dual utility in electrochemical applications and heavy metal adsorption, contributing to environmental remediation and reducing reliance on non-renewable resources.

The etching effect of oxygen during the cooling process of graphene CVD synthesis

Chemical vapor deposition provides a promising approach for the growth of large-area, high-quality graphene on Cu substrates. Oxygen plays either positive or negative roles for graphene synthesis, which have been extensively investigated predominantly focusing on graphene nucleation and growth stages. This study investigates the influence of oxygen during the cooling phase and demonstrates that graphene is more resistant to oxygen at higher temperatures but becomes susceptible to etching as the temperature decreases, unless it is too low. Thermodynamic simulations reveal that at elevated temperatures, oxygen is consumed by methane in the gas phase, leading to the generation of reactive carbon species that promote graphene growth and inhibit etching. Additionally, the etching reactivity of graphene is found to be correlated with the surface orientation of the underlying Cu grains. These findings suggest that defects in graphene can arise during the cooling stage if oxidant impurities in the atmosphere are not adequately controlled. Strategies to suppress graphene etching during cooling, such as reducing oxidant impurities and increasing cooling rates, are also presented.

Upcycling linear low-density polyethylene waste to turbostratic graphene for high mass loading supercapacitors

Linear low-density polyethylene (LLDPE) waste is difficult to upcycle into more valuable carbon materials because it tends to completely decompose into small molecules during thermal processing. In this work, LLDPE is upcycled into a high quality turbostratic graphene using a pre-treatment step to oxidatively crosslink the polymer with the assistance of solid additives (KCl and K2CO3) that improve crosslinking by increasing the effective surface area of the polymer melt during processing. After this pretreatment step, the crosslinked polymer could then be carbonized and catalytically graphenized between 400–950 °C without decomposition of the polymer feedstock. The LLDPE derived graphene (LLDPE-G) obtained from this process has a Brunauer–Emmett–Teller (BET) specific surface area, up to 1800 m2 g−1 and average Raman ID/IG and I2D/IG ratios of 0.85 and 0.57, respectively, indicating high quality graphene. When used as an electrode material in symmetric supercapacitors, LLDPE-G possesses a specific capacitance up to 175 Fg−1 at a mass loading of 20 mgcm−2, which is two times the commercial requirement, yielding an areal capacitance of 3.5 Fcm−2. Moreover, LLDPE-G exhibits exceptional cycling stability with a capacitance retention of 95.8 % after 100,000 cycles at a current density of 4.0 Ag−1. Additionally, the KCl and K2CO3 solids are recycled and reused over 3 complete reaction cycles to make new LLDPE-G with the material quality and electrocapacitive performance retained and verified after each cycle. Our approach creates new opportunities for upcycling waste LLDPE and other varieties of polyethylene into a higher value graphene used for electrochemical energy storage applications.

Memristors with Monolayer Graphene Electrodes Grown Directly on Sapphire Wafers.

The development of the memristor has generated significant interest due to its non-volatility, simple structure, and low power consumption. Memristors based on graphene offer atomic monolayer thickness, flexibility, and uniformity and have attracted attention as a promising alternative to contemporary field-effect transistor (FET) technology in applications such as logic and memory devices, achieving higher integration density and lower power consumption. The use of graphene as electrodes in memristors could also increase robustness against degradation mechanisms, including oxygen vacancy diffusion to the electrode and unwanted metal ion diffusion. However, to realize this technological transformation, it is necessary to establish a scalable, robust, and cost-effective device fabrication process. Here we report the direct growth of high-quality monolayer graphene on sapphire wafers in a mass-producible, contamination-free, and transfer-free manner, using a commercially available metal-organic chemical vapor deposition (MOCVD) system. By taking advantage of this approach, graphene-electrode based memristors are developed, and all the processes used in the device fabrication incorporating graphene electrodes can be performed at wafer scale. The graphene electrode-based memristor demonstrates promising characteristics in terms of endurance, retention, and ON/OFF ratio. This work presents a possible and viable route to achieving robust graphene-based memristors in a commercially and technologically sustainable manner, paving the way for the realization of more powerful and compact integrated graphene electronics in the future.

Fluid-Dynamics-Rectified Chemical Vapor Deposition (CVD) Preparing Graphene-Skinned Glass Fiber Fabric and Its Application in Natural Energy Harvest.

Graphene chemical vapor deposition (CVD) growth directly on target using substrates presents a significant route toward graphene applications. However, the substrates are usually catalytic-inert and special-shaped; thus, large-scale, high-uniformity, and high-quality graphene growth is challenging. Herein, graphene-skinned glass fiber fabric (GGFF) was developed through graphene CVD growth on glass fiber fabric, a Widely used engineering material. A fluid dynamics rectification strategy was first proposed to synergistically regulate the distribution of carbon species in 3D space and their collisions with hierarchical-structured substrates, through which highly uniform deposition of high-quality graphene on fibers in large-scale 3D-woven fabric was realized. This strategy is universal and applicable to CVD systems using various carbon precursors. GGFF exhibits high electrical conductivity and photothermal conversion capability, based on which a natural energy harvester was first developed. It can harvest both solar and raindrop energy through solar heating and droplet-based electricity generating, presenting promising potentials to alleviate energy burdens.

Decoupled High-Mobility Graphene on Cu(111)/Sapphire via Chemical Vapor Deposition.

The growth of high-quality graphene on flat and rigid templates, such as metal thin films on insulating wafers, is regarded as a key enabler for technologies based on 2D materials. In this work, the growth of decoupled graphene is introduced via non-reducing low-pressure chemical vapor deposition (LPCVD) on crystalline Cu(111) films deposited on sapphire. The resulting film is atomically flat, with no detectable cracks or ripples, and lies atop of a thin Cu2O layer, as confirmed by microscopy, diffraction, and spectroscopy analyses. Post-growth treatment of the partially decoupled graphene enables full and uniform oxidation of the interface, greatly simplifying subsequent transfer processes, particularly dry-pick up - a task that proves challenging when dealing with graphene directly synthesized on metallic Cu(111). Electrical transport measurements reveal high carrier mobility at room temperature, exceeding 104cm2V-1s-1 on SiO2/Si and 105cm2V-1s-1 upon encapsulation in hexagonal boron nitride (hBN). The demonstrated growth approach yields exceptional material quality, in line with micro-mechanically exfoliated graphene flakes, and thus paves the way toward large-scale production of pristine graphene suitable for high-performance next-generation applications.

Increasing the production of high-quality graphene nanosheet powder: The impact of electromagnetic shielding of the reaction chamber on the TIAGO torch plasma approach

Microwave-induced plasmas (MIPs), and specifically the TIAGO device (Torche à Injection Axiale sur Guide d’Ondes), offer a streamlined, cost-effective, and environmentally friendly technique for producing high-quality graphene powder in a reaction chamber by a single-step process through ethanol decomposition. To optimize graphene synthesis process, a pivotal move involves minimizing energy dissipation through radiation to maximize the available microwave energy input. Including a metallic shielding around the reaction chamber, essentially creating a Faraday cage, is proposed. The shielding strategy prevents radiation losses and results in a remarkable increase in solid material formation up to 22.8 %. This value, along with the emitted gases proportions and plasma volume increase, shows a correlation with conditions associated with higher input power. Crucially, the shielding of the reaction chamber does not modify graphene growth kinetics in the plasma, as confirmed by Optical Emission Spectroscopy. The synthesized material undergoes a thorough examination, employing diverse techniques like Raman spectroscopy, electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller (BET) analysis. These analyses underscore a consistent quality of graphene, unaffected by the shielding implementation. Therefore, electromagnetic shielding of the TIAGO torch discharge not only leads to a remarkable increase in solid material formation, thus energy yield, but does so without compromising the intrinsic properties and quality of the synthesized graphene.

One-Step Fabrication of Composite Hydrophobic Electrically Heated Graphene Surface

Ice accumulation poses considerable challenges in transportation, notably in the domain of general aviation. The present study combines the strengths and limitations of conventional aircraft deicing techniques with the emerging trend toward all-electric aircraft. This study aims to utilize laser-induced graphene (LIG) technology to create a multifunctional surface, seamlessly integrating hydrophobic properties with efficient electrical heating to mitigate surface icing effectively. We investigated the utilization of a 10.6 μm CO2 laser for direct writing on polyimide (PI), a widely used insulating encapsulation material. From the thermomechanical perspective, our initial analysis using COMSOL Multiphysics software (V5.6) revealed that when the laser power P exceeds 5 W, the PI substrate experiences ablative damage. The experimental results show that when P ≤ 5 W, an increase in power has a positive impact on the quality, surface porosity, roughness reduction, line-spacing reduction, and water contact-angle enhancement of the graphene. Conversely, when P > 5 W, higher power negatively affects both the substrate and the graphene structure by inducing excessive ablation. However, it influences the graphene line height positively and is consistent with overall experimental–simulation congruence. Furthermore, the incorporation of high-quality graphene resulted in a surface that exhibited higher contact angles (CA > 120°), lower energy consumption, and higher heating efficiency compared to the use of traditional electrically heated materials for anti-icing applications. The potential applications of this one-step fabrication method extend across various industries, particularly aviation, marine engineering, and other ice-prone domains. Moreover, the method has extensive prospects for addressing pivotal challenges associated with ice formation and serves as an innovative and efficient anti-icing technology.

Conveyor CVD to high-quality and productivity of large-area graphene and its potentiality

The mass production of high-quality graphene is required for industrial application as a future electronic material. However, the chemical vapor deposition (CVD) systems previously studied for graphene production face bottlenecks in terms of quality, speed, and reproducibility. Herein, we report a novel conveyor CVD system that enables rapid graphene synthesis using liquid precursors. Pristine and nitrogen-doped graphene samples of a size comparable to a smartphone (15 cm × 5 cm) are successfully synthesized at temperatures of 900, 950, and 1000 °C using butane and pyridine, respectively. Raman spectroscopy allows optimization of the rapid-synthesis conditions to achieve uniformity and high quality. By conducting compositional analysis via X-ray photoelectron spectroscopy as well as electrical characterization, it is confirmed that graphene synthesis and nitrogen doping degree can be adjusted by varying the synthesis conditions. Testing the corresponding graphene samples as gas-sensor channels for NH3 and NO2 and evaluating their response characteristics show that the gas sensors exhibit polar characteristics in terms of gas adsorption and desorption depending on the type of gas, with contrasting characteristics depending on the presence or absence of nitrogen doping; nitrogen-doped graphene exhibits superior gas-sensing sensitivity and response speed compared with pristine graphene.

Highly efficient and responsive thin heaters based on CVD graphene/polyetherimide nanolaminates for next-gen thermal management applications

Graphene, with its superior physical properties, has been considered as the perfect candidate for the production of lightweight, high-strength composite materials with interesting multi-functionalities. The use of large-sized, high-quality CVD graphene monolayers alternated to ultra-thin polymer films in a laminate configuration has been recently proposed as an efficient route to overcome many of the limitations faced by the use of discontinuous sheets of graphene in nanocomposites. Here we report on the production of CVD graphene/polyetherimide (Gr/PEI) nanolaminates with very low graphene volume fractions (up to 0.165 vol%), using a modified iterative and automatic lift-off/float-on procedure. The produced freestanding Gr/PEI nanolaminates present not only a significant enhancement of mechanical and electrical properties but, very interestingly, show impressive Joule heating efficiency. In fact, upon the application of an electrical potential, they can reach temperatures higher than 250 °C, with heating rates up to 325 °C/s. The produced heaters show a very uniform distribution of the temperature even when bend and are characterized by low power consumptions (up to 16 Watt) and high areal power densities (up to ca. ∼1.28 W/cm2), thus suggesting their possible application in thermal management.

(Invited) Plasma Designing of Hybrid 2D Graphene: A Green Approach for Future Energy Materials

The global research interest in two-dimensional (2D) materials and their derivatives has increased significantly, driven by the requirements of application-oriented materials for different sectors, including energy storage. Among the various classes of material groups, 2D layered materials have emerged as a critical research area due to their high aspect ratio, open edge boundaries, high surface-to-volume ratios, and mechanical and electrical properties. Graphene is a widely researched 2D class material with an atomically thin structure, excellent electronic properties, very high intrinsic mobility and exceptional thermal and electrical conductivity1. Even though the research on the electronic properties of graphene is explored very well and in a matured state, the studies on non-electronic properties are still in the budding phase. One of the significant obstacles to extending the studies of graphene to different fields is the cost-effective and environmentally friendly large-scale synthesis and processing of high-quality graphene. Thus, a cutting-edge approach for probing graphene structures at the atomic scale is required to produce high-quality graphene for next-generation applications. As an alternative progressive technique, plasma-enabled methods have emerged as safe and green approaches to tailor different graphene structures at the nanoscale. During graphene production, plasma assembles the nanostructures from gaseous into a solid form or converts solid precursor to graphitic form 2,3. Besides, plasma techniques open up the possibility of tailoring the properties by crafting heteroatoms to the graphene lattice, which is beneficial for energy storage applications4. Therefore, this paper introduces the advantages of plasma-enabled techniques in designing graphene-based materials with different morphologies and orientations and tailoring them at the nanoscale using heteroatoms. Such plasma-assisted techniques ensure the high structural quality of graphene and controllability in the hybrid morphologies, making them frontrunner energy storage applications. Plasma also offers the production of graphene directly on any substrate surface, gives a new direction to designing binder-free electrodes for energy-related applications, and could be used as a competitive alternative approach to the widely known wet chemical procedures to design advanced graphene electrode materials for next-generation energy storage devices.Reference Geim, A. K. Graphene: Status and prospects. Science (1979) 324, 1530–1534 (2009).Dias, A. et al. N-Graphene-Metal-Oxide(Sulfide) hybrid Nanostructures: Single-step plasma-enabled approach for energy storage applications. Chemical Engineering Journal 430, 133153 (2022).Jagodar, A. et al. Growth of graphene nanowalls in low-temperature plasma: Experimental insight in initial growth and importance of wall conditioning. Appl Surf Sci 643, 158716 (2024).Santhosh, N.M. et al. N-Graphene Nanowalls via Plasma Nitrogen Incorporation and Substitution: The Experimental Evidence. Nanomicro Lett 12, 53 (2020).

Synthesis, structure characterization, and electrochemical hydrogen storage of reduced graphene oxide and graphene

In the current study, multi-layer graphene (MLG) and reduced graphene oxide (rGO) were effectively synthesized and characterized by several techniques, including FT-IR, XRD, TGA, CHNS/O Analyzer, Raman spectroscopy, UV–Vis spectroscopy, TEM, and SEM. The electrochemical hydrogen storage (EHS) capacity was measured through cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS). High-quality graphene (ID/IG < 0.16), obtained from the simple liquid phase exfoliation method, exhibited a remarkable hydrogen storage capacity, reaching up to 200 F g−1 which equals 0.1 wt%. Furthermore, MLG outperforms rGO in terms of coulombic efficiency, achieving 100% in 10 cycles as opposed to rGO's 50% under identical conditions. This study presents the first-ever EHS using a new method that shows promising results.