Growth Mechanism Of Graphene Research Articles

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.

Molecular dynamics simulation study of graphene synthesis by rotating arc plasma

The rotating arc plasma method, based on its unique characteristics, provides a simple, efficient, and catalyst-free approach for graphene material synthesis. This study employs molecular dynamics simulations to theoretically investigate the detailed growth process of graphene at the atomic scale using plasma. During the growth process, different radicals serve as dissociation precursors within the plasma. Simulation results indicate that the growth process of graphene clusters involves three stages: extension of carbon clusters, cyclization of carbon chains, and coalescence of clusters into sheets. Firstly, the precursor concentration affects the size of graphene clusters; increasing the precursor concentration enlarges the cluster size but also increases the likelihood of curling. Secondly, increasing the hydrogen content in the precursor can reduce the growth rate of clusters, decrease dangling bonds at the periphery of clusters, thereby slowing down cluster closure and maintaining a well-defined sheet structure. Lastly, appropriately elevating the simulation temperature can enhance the reaction rate during the simulation process without altering the reaction pathway. These research findings establish the foundation for understanding the growth mechanism of graphene.

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.

Influence of deposition temperature and hydrogen on sustainable and transfer-free graphene transparent electrode for organic solar cells

The transfer-free graphene transparent conducting electrode (TCE) is a promising alternative to indium tin oxide (ITO) for organic solar cells (OSCs). In the present work, a comprehensive investigation on how deposition temperature and H2 flow rates affect the growth, structural, optical, and electrical properties of graphene produced by RF plasma enhanced chemical vapor deposition using sustainable sources was conducted. Inverted-geometry OSCs with P3HT: PCBM photoactive layer were fabricated on transfer-free graphene TCEs developed under different conditions. Moreover, the coupling of silver nanowires (AgNWs) with different graphene films was studied for hybrid graphene-AgNWs TCEs for OSCs. Devices based on graphene TCEs prepared at low or zero H2 flow have shown better performances than those at high flow of H2. Similarly, graphene TCEs prepared at high temperature (>700 °C, on quartz) led to a deteriorated device performance due to the highly increased growth of vertically oriented graphene nanosheets, which dramatically reduced film transmittance and increased surface roughness. The present work provides solid understanding of the growth mechanism of RF-PECVD graphene on glass from a sustainable carbon source. More importantly, the sustainable, ecofriendly, cost- and time-effective production of scalable transfer-free graphene TCEs for OSCs is optimized which paves the way towards ITO-free optoelectronics.

An alternative mechanism of dry reforming enhanced growth of high-quality graphene: CO2-assisted CVD

The Cu-CH4-CVD system is a common method for the preparation of large-area and high-quality graphene, but high preparation temperature is usually essential to provide the high energy required to obtain active carbon species, causing inevitable intrinsic pollution. Here, we demonstrated a new technique for the high-quality preparation of graphene and proposed a new nucleation growth mechanism of graphene on the experimental basis in combination with computational materials science. By introducing CO2 into the traditional CVD system, the problem of intrinsic pollution was solved while the graphene-shaping nuclear energy was reduced, and Gr films with few layers, large domain size and small defect density were prepared. Ultimately, the Schottky PD composed of the prepared Gr film and Ge film achieved 1550 nm photoelectric detection and showed good performance.

Controllable Synthesis and Growth Mechanism of Interlayer-Coupled Multilayer Graphene.

The potential applications of multilayer graphene in many fields, such as superconductivity and thermal conductivity, continue to emerge. However, there are still many problems in the growth mechanism of multilayer graphene. In this paper, a simple control strategy for the preparation of interlayer-coupled multilayer graphene on a liquid Cu substrate was developed. By adjusting the flow rate of a carrier gas in the CVD system, the effect for finely controlling the carbon source supply was achieved. Therefore, the carbon could diffuse from the edge of the single-layer graphene to underneath the layer of graphene and then interlayer-coupled multilayer graphene with different shapes were prepared. Through a variety of characterization methods, it was determined that the stacked mode of interlayer-coupled multilayer graphene conformed to AB-stacking structure. The small multilayer graphene domains stacked under single-layer graphene was first found, and the growth process and growth mechanism of interlayer-coupled multilayer graphene with winged and umbrella shapes were studied, respectively. This study reveals the growth mechanism of multilayer graphene grown by using a carbon source through edge diffusion, paving the way for the controllable preparation of multilayer graphene on a liquid Cu surface.

Unveiling the site-dependent characteristics and atomic mechanism of graphene growth on the polycrystalline diamond: Insight from the experiments and ReaxFF studies

The synthesis of graphene on functional materials has been an issue of great interest in the field of new-functional nanomaterials. As a promising semiconductor and mechanical material, the need for direct growing graphene on the polycrystalline diamond for modification has been strongly inspired nowadays. Herein, we completed the catalytic thermal annealing synthesis of graphene on the polycrystalline diamond without any additional carbon source, and the site-dependent growth characteristics of graphene on the diamond materials were captured. To explain such growth characteristics in detail, the graphene in-situ growth mechanism based on the polycrystalline diamond surface was clarified for the first time by using the reactive molecular dynamics method. Essentially, the growth mechanism of graphene in the vicinity of the diamond grain boundary follows the principle of “counter-precipitation”. Furthermore, the graphene growth is driven by the amorphization of the diamond lattice, and the pristine diamond surface has been proven can be used as the only solid carbon source to accomplish the growth of graphene on it. By contrast, the grain boundary plays the role of supplementary solid carbon source to accelerate the graphene growth rate during the graphene growth, which is the underlying cause of the site-dependent growth characteristics of graphene on the polycrystalline diamond.

Theoretical insights on the effect of alloying with Co in the mechanism of graphene growth on a Cu[sbnd]Co (1 1 1) catalyst

Alloying Cu catalyst with transition metals with high C solubility is an effective technique for growing graphene with a precisely controlled number of layers. Co is a transition metal with high C solubility and is suitable for alloying with Cu catalysts due to its similar atomic size. In this study, we elucidate the mechanism of graphene growth on a CuCo(111) catalyst by evaluating the energetics, thermodynamics, and kinetics of potential C source species, CHi (i = 0, 1, 2, 3), using a first-principles method. Alloying Cu with Co atoms upshifts the d-band center, which induces a robust p-d hybridization between the CuCo(111) catalyst and the C source species. From relative population calculations, it is found that the C monomer on the catalyst subsurface always becomes dominant in the range of growth conditions studied. Therefore, the C monomer in the catalyst subsurface controls the segregation growth mechanism. In addition, it is found that the diffusion of C monomer into the CuCo(111) catalyst subsurface is an exothermic process with a low activation energy. These results enable us to suggest a novel alternating alloy catalyst for growing few-layer graphene with a precisely controlled number of layers.

Multiscale Model of CVD Growth of Graphene on Cu(111) Surface.

Due to its outstanding properties, graphene has emerged as one of the most promising 2D materials in a large variety of research fields. Among the available fabrication protocols, chemical vapor deposition (CVD) enables the production of high quality single-layered large area graphene. To better understand the kinetics of CVD graphene growth, multiscale modeling approaches are sought after. Although a variety of models have been developed to study the growth mechanism, prior studies are either limited to very small systems, are forced to simplify the model to eliminate the fast process, or they simplify reactions. While it is possible to rationalize these approximations, it is important to note that they have non-trivial consequences on the overall growth of graphene. Therefore, a comprehensive understanding of the kinetics of graphene growth in CVD remains a challenge. Here, we introduce a kinetic Monte Carlo protocol that permits, for the first time, the representation of relevant reactions on the atomic scale, without additional approximations, while still reaching very long time and length scales of the simulation of graphene growth. The quantum-mechanics-based multiscale model, which links kinetic Monte Carlo growth processes with the rates of occurring chemical reactions, calculated from first principles makes it possible to investigate the contributions of the most important species in graphene growth. It permits the proper investigation of the role of carbon and its dimer in the growth process, thus indicating the carbon dimer to be the dominant species. The consideration of hydrogenation and dehydrogenation reactions enables us to correlate the quality of the material grown within the CVD control parameters and to demonstrate an important role of these reactions in the quality of the grown graphene in terms of its surface roughness, hydrogenation sites, and vacancy defects. The model developed is capable of providing additional insights to control the graphene growth mechanism on Cu(111), which may guide further experimental and theoretical developments.

Direct conversion of CO2 to graphene via vapor–liquid reaction for magnesium matrix composites with structural and functional properties

Converting CO 2 to valuable materials is attractive in environmental protection and resource utilization. In this study, a vapor–liquid interface reaction system for mass production of high-quality graphene is reported. The graphene obtained has high crystallinity and few defects during the reaction of CO 2 and Mg melt. The growth mechanism of graphene is demonstrated in vapor–liquid interface area by combining the CO 2 bubbles as a soft template to guide growth with the confinement effect of dense MgO nanoparticles. The quality of the graphene is verified by epoxy composites with high electromagnetic shielding effectiveness. Additionally, the V–L reaction method ingeniously solves the dispersion of graphene in metal, providing a preparation strategy of Mg matrix composites with structure and function integration.

Low-Temperature Direct Growth of Nanocrystalline Multilayer Graphene on Silver with Long-Term Surface Passivation.

A wide variety of transition metals, including copper and gold, have been successfully used as substrates for graphene growth. On the other hand, it has been challenging to grow graphene on silver, so realistic applications by combining graphene and silver for improved electrode stability and enhanced surface plasmon resonance in organic light-emitting diodes and biosensing have not been realized to date. Here, we demonstrate the surface passivation of silver through the single-step rapid growth of nanocrystalline multilayer graphene on silver via low-temperature plasma-enhanced chemical vapor deposition (PECVD). The effect of the growth time on the graphene quality and the underlying silver characteristics is investigated by Raman spectroscopy, X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), and cross-sectional annular dark-field scanning transmission electron microscopy (ADF-STEM). These results reveal nanocrystalline graphene structures with turbostratic layer stacking. Based on the XPS and ADF-STEM results, a PECVD growth mechanism of graphene on silver is proposed. The multilayer graphene also provides excellent long-term protection of the underlying silver surface from oxidation after 5 months of air exposure. This development thus paves the way toward realizing technological applications based on graphene-protected silver surfaces and electrodes as well as hybrid graphene-silver plasmonics.

Effect of Ni atomic fraction on active species of graphene growth on Cu-Ni alloy catalysts: a density functional theory study.

Cu-Ni alloys are promising catalysts for precisely controlling the number of graphene layers grown by chemical vapor deposition (CVD). However, the theoretical understanding of the effect of the Ni atomic fraction on the active species, which helps determine the mechanism of graphene growth, is still limited. Here, we examine the energetics, electronic properties, and populations of potential carbon source species (CH3, CH2, CH, C) on Cu-Ni alloy catalysts with various Ni atomic fractions under various CVD growth conditions using density functional theory combined with atomistic thermodynamics. An increased Ni atomic fraction of the Cu-Ni alloy catalyst increases the d-band center and d-orbital delocalization of the Ni atoms. Therefore, the stability of the carbon source adsorbed on the surface and subsurface of the catalyst increases. Relative population analysis shows that the CH and C monomers on the surface are the active species that drive surface-mediated growth on Cu-Ni catalysts with low Ni atomic fractions. The dominance of CH and C species can be further tuned by adjusting the growth temperature and partial pressure of H2. In contrast, in a Cu-Ni catalyst with a high Ni atomic fraction, the C monomer species on the subsurface has high stability and acts as an active species that controls the cooling-induced segregation growth mechanism. This study provides an essential insight into the atomistic mechanism of graphene growth in Cu-Ni alloy catalysts.

Mechanism of crack propagation in penta-graphene

Penta graphene has attracted much attention due to its unique carbon atom topology and novel properties in these years. In this paper, we study the crack growth and material fracture mechanism of penta graphene under uniaxial tension systematically via molecular dynamics simulation. We explore the mechanism of stress field and influencing factors during crack growth on penta graphene. The mechanical properties of penta graphene and graphene are compared and analyzed. The effect of temperature on the mechanical properties of penta graphene is analyzed by comparing the strain-stress curves at various temperatures. The Young's modulus of penta graphene at fracture time are discussed, and we reveal that the temperature influence on Young's modulus before fracture. By designing initial cracks of different lengths on penta graphene, we investigate into the variation of stress field at both crack tips on penta graphene under stress stretching. The mechanism of crack growth and propagation on penta graphene is uncovered with more details from atomic perspective. It is found that the stress fields are concentrated on various parts on penta graphene with the different crack length. During the growth of short cracks, the stress field mainly concentrates on the crack tip during all the process. In the process of the growth of longer cracks, the stress field will first focus on the section of the crack, and then transfer to the crack tip and begin to grow and propagate around. By analyzing the reduced energy release rate during crack growth and fracture, it is suggested that the lower atomic binding energy weakens the fracture strength of penta graphene, and thus affects the mechanical properties of penta graphene.

Controlled growth of large-area monolayer graphene on Ni (110) facet: Insight from molecular dynamics simulation

To achieve the controlled synthesis of high-quality graphene/nickel heterostructure in practice, the study of the atomistic mechanism of graphene growth on the Ni (110) facet whose lattice mismatches with graphene is indispensable. A series of molecular dynamics simulations based on the modified interatomic force field were performed to provide an insightful understanding of the process of graphene growth by chemical vapor deposition. Herein, the dissolution and precipitation mechanism of graphene in the initial stage of growth on Ni (110) has been demonstrated, followed by the dynamic evolution of graphene growth was elucidated. The effects of carbon deposit rate and annealing temperature on graphene growth were investigated in-depth, and the optimum carbon deposit rate and temperature in theory for homogeneous monolayer graphene growth on Ni (110) facet were determined. Furthermore, two self-healing routes of defects of embedded C-chain and C-heptagon for high-temperature catalyzed were analyzed. Lastly, the relevance of the chemical vapor deposition technique was discussed in terms of the actual deposition process. The theoretical investigations and practical discussions can provide an instructive reference for optimizing chemical vapor deposition processing conditions in preparing homogeneous monolayer graphene on the Ni (110) facet.

In situ observations of graphene growth and strong graphene‑nickel interactions by grazing incidence X-ray diffraction

The growth mechanisms of graphene on polycrystalline Ni by chemical vapor deposition using polymethyl methacrylate (PMMA) as solid-state carbon sources were investigated by in-situ two-dimensional grazing incidence X-ray diffraction (GIXRD). The results show that the formation of graphene can be described by four stages: The graphitization of solid-state carbon, carbon dissolution in Ni, graphene nucleation, and isothermal growth of graphene, suggesting that the graphitization mechanism is metal-induced crystallization (MIC) mechanism. The so-called induction is mutual, that is, Ni induces the growth of graphene, and reciprocally, graphene induces the rotation and reorientation of Ni. The reorientation of Ni is the enhancement of Ni(111). The rotation and reorientation of Ni occur simultaneously with the nucleation of graphene and continue throughout the growth of graphene. The rotation of Ni ends when the graphene growth stops. Further, the forces causing the rotation and reorientation of the surface Ni lattice are analyzed. It was discovered for the first time that grain rotation was caused by directional carbon diffusion and graphene-Ni interaction. In addition, when the growth temperature is the same, the time when graphene starts to grow is mainly related to the nickel matrix but not the carbon source.

Bottom‐Up Growth of Graphene Nanospears and Nanoribbons

One dimensional graphene nanostructures are one of the most promising materials for next generation electronics. Here, the chemical vapor depostion growth of graphene nanoribbons (GNRs) and graphene nanospears (GNSs) on a copper surface is reported. The growth of GNRs and GNSs is enabled by a vapor–liquid–solid (VLS) mechanism guided by on-surface propagation of a liquid Cu-Si catalyst particle. The slow lateral growth and the fast VLS vertical growth give rise to spear head-shaped GNSs. In situ observations further confirm that the lateral graphene growth can be completely suppressed and thus GNRs are grown. The synthesized field effect transistor (FET) devices show that the GNRs and GNSs have high carrier mobilities of ≈2000 cm2 V−1 s−1. Both FET and Kelvin probe force microscopy measurements confirm that the Fermi levels of the synthesize GNSs shift downward from the wide part to the tip is strongly p-doped. These findings yield key insights into the growth mechanism of graphene and open a door for achieving a facile and scalable method of synthesizing free standing GNRs and GNSs and their applications, such as the Fermi-level tunable devices.

Ice Crystal Growth Mechanism and Structure-activity Relationships of Graphene Oxide/Poly(vinyl alcohol) Aerogels

Ice Crystal Growth Mechanism and Structure-activity Relationships of Graphene Oxide/Poly(vinyl alcohol) Aerogels

Multigraphene Prepared by One-Pot Pyrolysis of Diatomite/Polypropylene Composites

Multigraphene was prepared via a one-pot pyrolysis method using polypropylene (PP) as the carbon source and diatomite (DM) as the catalyst. The obtained graphene had 4–6 layers and a D/G intensity ratio of 0.70 and a 2D/G intensity ratio of 0.72, indicating a high degree of graphitization. When the pyrolysis temperature was higher than 850 °C under argon, the graphene yield was greatly dependent on the DM content. The highest graphene yield of 25.86% was obtained by pyrolysis of PP with 30 wt.% DM at the temperature of 1000 °C. A catalytic effect of DM and infusible cross-linking structure formation were proposed to explain the possible mechanism of graphene growth during the pyrolysis of the DM/PP composites.

Graphene on Nanoscale-Thick Au Films: Implications for Anticorrosion in Smart Wearable Electronics

Gold is normally considered inert to chemical reaction. Nevertheless, as a common electrode material, it would suffer from corrosion when exposed to certain solutions such as sweat and body fluids. Here, we report low-temperature plasma-enhanced chemical vapor deposition (PECVD) of graphene on gold and demonstrate its feasibility for anticorrosion application. The effects of hydrogen-to-methane ratio and the underlying gold substrate on the graphene growth are investigated, and the growth mechanism of PECVD graphene on gold is proposed. When immersed in an oxygenated saline solution, the PECVD-grown graphene-covered gold surface is found to remain intact after an acceleration soaking test at 90 °C for 24 h, which is in contrast to the degradation of bare gold surface subject to the same test. Our findings suggest that consumer/medical wearables and implantable devices with exposed gold can benefit from the protection of a direct, low-temperature PECVD-grown graphene layer for anticorrosion, thereby prolonging the efficacy and reliability of gold electrode-based biosensors.

In Situ Investigating the Mechanism of Graphene Growth by Chemical Vapor Deposition

In Situ Investigating the Mechanism of Graphene Growth by Chemical Vapor Deposition