High-quality Graphene Research Articles

Application of digital twins for simulation based tailoring of laser induced graphene

In the era of man–machine interfaces, digital twins stand as a key technology, offering virtual representations of real-world objects, processes, and systems through computational models. They enable novel ways of interacting with, comprehending, and manipulating real-world entities within a virtual realm. The real implementation of graphene-based sensors and electronic devices remains challenging due to the integration complexities of high-quality graphene materials with existing manufacturing processes. To address this, scalable techniques for the in-situ fabrication of graphene-like materials are essential. One promising method involves using a CO2 laser to convert polyimide into graphene. Optimizing this graphitization process is hindered by complex parameter interactions and nonlinear terms. This article explores how these digital replicas can enhance the fabrication of laser-induced graphene (LIG) through laser simulation and machine learning methods to enable rapid single-step LIG patterning. This approach aims to create a universal simulation for all CO2 lasers, calculating optical energy flux and utilizing machine learning to control and predict LIG conductivity (ability to conduct current), morphology, and electrical resistance. The proposed procedure, integrating digital twins in the LIG production process, will avoid or reduce the preliminary tests required to determine the proper laser parameters to reach the desired LIG characteristics. Accordingly, this approach will reduce the time and costs associated with these tests and thus increase the efficiency and optimize the procedure.

Toward the Production of Super Graphene.

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Synthesis of Microscopic 3D Graphene for High-Performance Supercapacitors with Ultra-High Areal Capacitance.

Despite graphene being considered an ideal supercapacitor electrode material, its use in commercial devices is limited because few methods exist to produce high-quality graphene at a large scale and low cost. A simple method is reported to synthesize 3D graphene by graphenization of coal tar pitch with a K2CO3 catalyst. This produces 3D graphenes with high specific surface areas up to 2113 m2 g-1 and exceptional crystallinity (Raman ID/IG as low as ≈0.15). The material has an outstanding specific capacitance of 182.6 F g-1 at a current density of 1.0 A g-1. This occurs at a mass loading of 30mg cm-2 which is 3 times higher than commercial requirements, yielding an ultra-high areal capacitance of 5.48 F cm-2. The K2CO3 is recycled and reused over 10 cycles with material quality and electrocapacitive performance of 3D graphene retained and verified after each cycle. The synthesis method and resulting electrocapacitive performance properties create new opportunities for using 3D graphene more broadly in practical supercapacitor devices.

Silicon oxide particles size evolution during CVD graphene growth on Cu substrates

Chemical vapor deposition (CVD) on metal substrates is presently the remarkably route for the synthesis of high-quality continuous graphene films at a large scale. Whereas, during the thermal processing procedure in the quartz tube, the formation of silicon oxide particles would degrade the performance of graphene. To better understand the origin of these particles , a series of CVD graphene growth experiments with were conducted on the Cu substrates. In this paper, we investigated the main component and morphology of the particles by X-Ray photoelectron spectroscopy (XPS), energy dispersive spectrometry (EDS) measurement in scanning electron microscopy (SEM) and revealed that the silicon oxide particles gradually increased in diameter across the graphene films on the Cu surface, which was found to be correlated with the working time of the quartz products. Raman spectroscopy was also applied to prove the drawback consequence of the contamination on the quality of the CVD graphene film. To mitigate this issue, we further propose a modification of the CVD system that a coaxial alumina or BN tube inside the quartz tube to screen the contaminants bringing about improved graphene growth.

Improved photoelectrochemical performance of tungsten-catalyzed graphene nanoplatelet electrodes prepared by hot-wire chemical vapor deposition at low substrate temperatures

The current increase in demand for graphene in various energy applications such as electrode materials for supercapacitors, batteries, thermoelectric, and hydrogen production via water-splitting, the production of high-quality graphene, considering its fascinating physical and electrical properties, high-yield, and large-area has becoming more challenging at the research and development level. Therefore, in this work, graphene nanoplatelets (GNPs) were directly grown on tungsten nanoparticle (W NP)-coated p-type crystalline silicon and quartz substrates using hot-wire chemical vapor deposition at low substrate temperatures (<500 °C). Prior to the GNP deposition, a plasma process was employed to induce the formation of W NPs, which act as a metal catalyst for facilitating the growth of large-area and multi-layer GNPs. The W NPs were formed at substrate temperatures ranging from 250 to 550 °C, with the largest graphene sheet was grown at 450 °C. Higher substrate temperatures promote the growth of high-quality graphene layers with high intensities of G (IG) and 2D bands (I2D), and high I2D/IG ratio values. The GNP photoelectrode prepared at 450 °C demonstrated better photoelectrochemical responses with the highest photocurrent density of 1.65 mA/cm2 at 1.5 VAg/AgCl, the lowest charge transfer resistance (14.0 kΩ), and the highest donor density (2.57 × 10 28 cm−3) compared to the tungsten carbide thin film and W NP electrodes prepared at the same temperature. The effects of substrate temperature on the optical, structural, and photoelectrochemical properties of the as-grown GNPs are discussed.

Overcoming the Incompatibility Between Electrical Conductivity and Electromagnetic Transmissivity: A Graphene Glass Fiber Fabric Design Strategy.

Conventional conductive materials such as metals are crucial functional components of conductive systems in diverse electronic instruments. However, their severe intrinsic impedance mismatch with air dielectric causes strong reflection of incident electromagnetic waves, and the resulting low electromagnetic transmissivity typically interferes with surrounding electromagnetic signal communications in modern multifunction-integrated instruments. Herein, graphene glass fiber fabric (GGFF) that merges intrinsic electrical and electromagnetic properties of graphene with dielectric attributes and highly porous macrostructure of glass fiber fabric (GFF) is innovatively developed. Using a novel decoupling chemical vapor deposition growth strategy, high-quality and layer-limited graphene is prepared on noncatalytic nonmetallic GFF in a controlled manner; this is pivotal to realizing GGFF with the desired compatibility among high conductivity, low electromagnetic reflectivity, and high electromagnetic transmissivity. At the same sheet resistance over a wide range of values (250-3000 Ω·sq-1), the GGFF exhibits significantly lower electromagnetic reflectivity (by 0.42-0.51) and higher transmissivity (by 0.27-0.62) than those of its metal-based conductive counterpart (CuGFF). The material design strategy reported herein provides a constructive solution to eliminate the incompatibility between electrical conductivity and electromagnetic transmissivity faced by conventional conductive materials, spotlighting the applicability of GGFF in electric heating scenarios in radar, antenna, and stealth systems.

Effect of growth conditions and reactor configuration on the growth uniformity of large-scale graphene by chemical vapor deposition

Chemical vapor deposition (CVD) is an affordable method for the preparation of large-scale and high-quality graphene. With the increase in CVD reactor size, gas mass transfer, flow state, and gas phase dynamics become more complicated. In this study, computational fluid dynamics is used to investigate factors affecting the uniformity of large-scale graphene growth under different growth conditions and reactor configurations. The dimensionless number defined in this paper and the Grashof number are utilized to distinguish the species transfer patterns and the flow states, respectively. A gas-surface dynamics model is established to simulate the graphene growth. Results reveal that the graphene growth rate uniformity is the highest at very low pressure and flow rate due to the flow symmetry and diffusion-dominated species transfer. At an increased pressure of 20 Torr, the uniformity of the graphene growth rate becomes higher axially and lower circumferentially with an increasing inlet mass flow rate. When the flow rate is fixed at 1500 SCCM and pressure is reduced from 20 to 2 Torr, graphene growth uniformity first increases and then decreases due to the influence of gas phase dynamics. Graphene growth rates are analyzed across ordinary reactor configurations and four configurations with inner tubes at 20 Torr pressure and 1500 SCCM flow rate. Comprehensive evaluation suggests that the ordinary reactor configuration performs best under these conditions. This research offers insights into the macroscopic growth mechanism of large-scale graphene and provides guidance for designing growth conditions in large-area graphene production.

Numerical investigation on the effect of gas-phase dynamics on graphene growth in chemical vapor deposition

Chemical vapor deposition (CVD) is a crucial technique to prepare high-quality graphene because of its controllability. In the research, we perform a systematic computational fluid dynamics numerical investigation on the effect of gas-phase reaction dynamics on the graphene growth in a horizontal tube CVD reactor. The research results indicate that the gas-phase chemical reactions in the CVD reactor are in a nonequilibrium state, as evidenced by the comparison of species mole fraction distributions during the CVD process and under chemical equilibrium conditions. The effect of gas-phase reaction dynamics on the deposition rate of graphene under different conditions is studied, and our research shows that the main causes of change in graphene growth rates under different conditions are gas-phase reaction dynamics and active species transport. The results of numerical simulation agree well with the experimental phenomena. The research results also indicate that, for methane, the main limiting factor of graphene growth is the surface kinetic reaction rate. Conversely, for active species, the main limiting factor of graphene growth is species transport. Our research suggests that the growth rate of graphene can be regulated from the perspective of the gas reaction mechanism. This method has theoretical guiding significance and can be extended to the preparation of large-area graphene.

Graphene nanoribbons grown in hBN stacks for high-performance electronics.

Van der Waals encapsulation of two-dimensional materials in hexagonal boron nitride (hBN) stacks is a promising way to create ultrahigh-performance electronic devices1-4. However, contemporary approaches for achieving van der Waals encapsulation, which involve artificial layer stacking using mechanical transfer techniques, are difficult to control, prone to contamination and unscalable. Here we report the transfer-free direct growth of high-quality graphene nanoribbons (GNRs) in hBN stacks. The as-grown embedded GNRs exhibit highly desirable features being ultralong (up to 0.25 mm), ultranarrow (<5 nm) and homochiral with zigzag edges. Our atomistic simulations show that the mechanism underlying the embedded growth involves ultralow GNR friction when sliding between AA'-stacked hBN layers. Using the grown structures, we demonstrate the transfer-free fabrication of embedded GNR field-effect devices that exhibit excellent performance at room temperature with mobilities of up to 4,600 cm2 V-1 s-1 and on-off ratios of up to 106. This paves the way for the bottom-up fabrication of high-performance electronic devices based on embedded layered materials.

Efficient and high-quality absorption enhancement using epsilon-near-zero cylindrical nano-shells constructed by graphene

This paper presents a detailed scattering analysis of a hollow-core plasmonic-shell cylindrical wire to design an efficient, compact, narrowband, and reconfigurable optical absorber. The shell is formed by a thin graphene material, investigated in its epsilon-near-zero (ENZ) plasmonic region. Compared to the graphene plasmonic resonances in the terahertz(THz)/far-infrared (FIR) frequencies, the ENZ plasmonic resonances offer a blue shift in the operating frequency of the second-order plasmonic resonances by increasing the geometrical dimensions. This feature is successfully used to design efficient optical wave absorbers with absorption cross-sections much larger than geometrical and scattering cross-sections. The observed blue shift in the resonance spectrum, which is the key point of the design, is further verified by defining each particle with its polarizability and fulfilling the resonant scattering condition in the framework of Mie’s theory. Furthermore, graphene relaxation time and chemical potential can be used to manipulate the absorption rate. Observed resonances have narrow widths, achieved with simple geometry. To consider more practical scenarios, the one-dimensional arrangement of the cylindrical elements as a dense and sparse array is also considered and the design key point regarding graphene quality is revealed. The quality factor of the sparse array resonance is 2272.8 and it demands high-quality graphene material in design. It is also observed that due to the use of small particles in the design, the near-field and cooperative effects are not visible in the absorption cross-section of the array and a clear single peak is attained. This polarization-insensitive absorber can tolerate a wide range of incident angles with an absorption rate above 90%.

A novel top-down approach for high yield production of graphene from natural graphite and its supercapacitor applications

The cost-effective and sustainable mass production of graphene is of utmost importance for its comprehensive application across various industries. Despite ball milling being the most efficacious method for obtaining high-quality graphene, industrial-scale production poses a significant challenge due to a lowered yield, heterogeneous media and reduced energy transfer efficiency. Furthermore, the consistent properties of graphene pose another major challenge when it comes to scaled-up processes. To address these challenges, we conducted a study aiming to produce high-quality graphene from natural graphite sourced from Indian ore through the utilisation of a horizontal planetary ball mill. Our analysis revealed that the graphene sheets produced via this method exhibit excellent structural integrity, rendering them highly beneficial for a wide range of applications. The diffraction pattern of the graphene sheets is dominated by the (002) plane, as shown by XRD data. The Raman spectrum indicates a compatible I2D/IG ratio, suggesting double- to triple-layer graphene sheets. The graphene sheets were seen to be layered and irregularly shaped in the SEM and TEM pictures, which is consistent with the sample's polycrystalline makeup. The findings demonstrate the large surface area and strong electrical conductivity of the synthesized graphene. Furthermore, the high specific capacitance value of 30F/g is shown by in-house graphene-based supercapacitors. Overall, the findings of this work show that manufacturing high-quality graphene from synthetic and natural graphite is feasible and effective when carried out on a horizontal planetary ball mill, and each batch of 200 g graphene requires $25 in production costs. This strategy promises to supply the rising demand for graphene by enabling more widespread, cost-effective manufacturing.

High-quality graphene devoid of oxygen functionalities as conductive ink for flexible electronics and bendable all-solid-state supercapacitors

High-yielding and scalable naphthalene-assisted ball-mill exfoliation of graphite is reported here aiming at the production of high-quality graphene cost-effectively. The Raman spectral analysis indicates less-defective graphene, whereas the few-layered nature is evident from the XRD pattern and AFM images. Monolayered graphene can also be produced upon ultrasonication, which is evident from the HRTEM images and Raman spectral analysis. XPS indicated the absence of in-plane oxygen functionalities that usually disrupt the aromatic π-conjugation. Graphene is effectively utilized here to formulate a conducting ink for polyimide tape-based wires for lighting LEDs. The supercapacitor performance of the graphene as an electrode material was also assessed, where, in the three-electrode system, graphene exhibited an excellent areal capacitance of 197.22 mF/cm2 at a current density of 2 mA/cm2 and the graphene-modified carbon paste electrode retained 100 % of initial capacitance even after 7500 charge-discharge cycles. A bendable supercapacitor was also fabricated here with graphene-coated carbon cloth electrodes that exhibited a high capacitance of 524.28 mF at 0.05 mA/cm2 with the highest energy and power densities of 14.87 μWh/cm2 and 349.76 μW/cm2 respectively. The bendable device retained 99.9 % of its initial capacitance after 3000 continuous cyclic voltammetric runs. The supercapacitor delivered the same performance as the straight device during bending, twisting and even after bending at different angles.

Graphene synthesis by electromagnetic induction heating: Domain size and morphology control

In this paper we discuss the effect of hydrogen and methane content during low-pressure chemical vapor deposition (LPCVD) of graphene on inductively heated copper foils. By increasing the H2/CH4 ratio by a factor of 5 from 25 to 125, different graphene morphologies ranging from dendritic fractals to compact hexagonal islands are obtained. In addition, increasing the hydrogen concentration allows the nucleation rate to be slowed down by a factor of ∼10 thereby high-quality regular hexagonal graphene single crystals of significant size of 0.1 mm are found. From these measurements, we estimate the activation energy for graphene nucleation in low-pressure CVD (2 eV) and propose a phenomenological law for graphene nucleation. As compared to conventional CVD methods, considerable advantages of inductive heating are outlined, and some fundamental aspects of this approach are discussed.

Flexible field-effect transistors with high-quality and uniform single-layer graphene for high mobility

In this work, a fully flexible graphene field-effect transistor with high carrier mobility is reported. Patterned high-quality and uniform single-layer graphene films are successfully realized by combining the selective growth on a patterned copper foil and the direct transfer method to minimize degradation factors. The selectively grown single-layer graphene is directly transferred to the target substrate through the deposition of poly-para-xylylene (Parylene) C. The quality of the graphene films is confirmed by Raman spectroscopy. The analysis reveals that the use of Parylene C as the substrate, gate dielectric, and encapsulation layer has the advantage of reducing the scattering by the optical phonons and charge puddles. The estimated residual carrier density is 1.72 × 1011 cm−2, and the intrinsic hole and electron carrier mobilities are found to be as high as 10 260 and 10 010 cm2 V−1 s−1, respectively. This study can pave the way for the development and mass production of high-performance and fully flexible graphene electronics.

Direct-Write Printed Slippery Surface for Assembling a High-Quality Graphene Structure and Its Application in Flexible Electric Actuators.

Graphene is a two-dimensional honeycomb-like nanomaterial generated by carbon atoms in sp2 hybridized orbitals to form a hexagonal lattice structure with excellent electrical, optical, and mechanical properties. The solution process method has been widely used to realize large-area patterned graphene structures for high-performance devices. In the method, graphene usually needs to be dispersed in solution, and the π-π bonding gravitational interactions between graphene sheets would lead to uncontrollable structures in solution and difficulty in obtaining high performance. In this work, a patterned graphene oxide (GO) structure with controllable thickness and layer spacing was realized by a direct-write printed slippery surface, which was used as a slippery limited template. After reducing GO into reduced graphene oxide (rGO), a flexible electric pattern with a conductivity of up to 6.425 × 103 S/m was realized. Furthermore, the patterned rGO structure was transferred on polydimethylsiloxane (PDMS), which could generate less than a 5% change in resistance after 10,000 consecutive bends, and an anisotropic expansion based on rGO and PDMS materials under electro-thermal coupling. The patterned rGO structures could meet the performance requirements of highly sensitive and complex deformation applications as flexible electric actuators. This study provides great research significance and application value for patterning high-quality graphene structures and realizing high-performance flexible electronic devices.

Binder assisted graphene derivatives as lubricants in copper: Improved tribological performance for industrial application

Originally derived from graphite, high-quality single-layer graphene is an excellent anti-wear and -friction additive in metal matrix. Here, the tribological performance of 3 different commercialized graphene derivatives (e.g., graphene oxide [GO], reduced graphene oxide [RGO], and graphene nanoplatelet [GNP]) as additives in a Cu matrix, were investigated from an industrial perspective. To increase the interaction of graphene derivatives with Cu particles, and addressing the aggregation problem of the graphene derivatives, different binders (polyvinyl alcohol [PVA] and cellulose nanocrystals [CNC]) were introduced into the system. Benefiting from such a strategy, a uniform distribution of the graphene derivatives in Cu matrix was achieved with graphene loading up to 5 wt%. After high-temperature sintering, the graphene is preserved and well distributed in the Cu matrix. It was found that the GNP-containing sample shows the most stable friction coefficient behavior. However, GO and RGO also improve the tribological performance of Cu under different circumstances.

Photo-thermoelectric effect-driven detection of optical communication light in graphene/hBN heterostructures

We report on the photodetection properties of high-quality graphene encapsulated by hexagonal boron nitride under illumination with optical communication light. We demonstrate a gate-tunable photocurrent and zero-bias switching cycle operation at RT. Through gate and temperature-dependent photocurrent measurements, we determine that the dominant photoresponse mechanism is the photo-thermoelectric effect. At low temperatures, the photocurrent in finite doping regions correlates with the Seebeck coefficient, while sharp peaks emerge near the charge neutrality point due to an edge-excited photocurrent. Our study provides guidelines for high-performance graphene-based optoelectronic devices.

Graphene-containing biocarbon from burlap waste: Property comparison with commercial grade graphene nanoplatelets

In this paper, we report a method for synthesizing high-yield graphene-containing biocarbon from burlap waste through a simple two-step carbonization process. The first step involves feedstock carbonization at 600 °C, followed by ball milling and then graphitization at 1200 °C using KOH. A comparative analysis between the obtained bio-graphene and commercial graphene revealed superior graphene properties of the burlap-based graphene. Notably, this bio-based graphene exhibited exceptional characteristics such as a very high BET surface area in the range of 1021 m²/g, low defect-to-graphene ratio of 0.12 in the Raman spectra, and an overall yield of 19% wt. These findings highlight the potential of burlap waste as a sustainable precursor for high-quality graphene synthesis and its potential for various applications.

Recent Advances in the Green Reduction of Graphene Oxide and its Potential Applications

Abstract: Graphene has drawn significant attention due to its commercial usage in various fields. Several methods have been developed for the synthesis of graphene sheets but most of them involve only lab-scale production and are expensive too. So, the production of high-grade graphene on a large scale by cost-efficient and eco-friendly methods is still a challenge for the scientific community. The reduction of graphene oxide to produce high-quality graphene is considered the most eco-efficient and auspicious approach. Various pathways for the reduction of graphene oxide involving chemical reduction, thermal annealing, microwave and photoreduction, solvothermal, electrochemical, and green reduction have been explored. Several of these methods use harmful and toxic reagents that cause adverse effects on human health and the environment. The reduction of graphene oxide by plant extracts is simple, easily accessible, environment-friendly, sustainable, renewable, and economical. This review highlights different approaches for the synthesis of reduced graphene oxide with the main focus on green reduction using plant extracts. Moreover, several applications of reduced graphene oxide in various fields have also been elaborated. The main aim of this review is to provide deep insights for current and future researchers related to the greener methods for the synthesis of reduced graphene oxide along with its potential applications.

Scalable Synthesis of Bilayer Graphene at Ambient Temperature.

In this work, we develop for the first time a facile chemical lithiation-assisted exfoliation approach to the controllable and scalable preparation of bilayer graphene. Biphenyl lithium (Bp-Li), a strong reducing reagent, is selected to realize the spontaneous Li-intercalation into graphite at ambient temperature, forming lithium graphite intercalation compounds (Li-GICs). The potential of Bp-Li (0.11 V vs Li/Li+), which is just lower than the potential of stage-2 lithium intercalation (0.125 V), enables the precise lithiation of graphite to stage-2 Li-GICs (LiC12). Intriguingly, the exfoliation of LiC12 leads to the bilayer-favored production of graphene, giving a high selectivity of 78%. Furthermore, the mild intercalation-exfoliation procedure yields high-quality graphene with negligible structural deterioration. The obtained graphene exhibits ultralow defect density (ID/IG ∼ 0.14) and a considerably high C/O ratio (∼29.7), superior to most current state-of-the-art techniques. This simple and scalable strategy promotes the understanding of chemical Li-intercalation methods for preparing high-quality graphene and shows great potential for layer-controlled engineering.