Kinetic Monte Carlo Modeling of Graphene Sheet Growth During CVD

Graphene is a material of key interest across several research fields. Bulk graphene synthesis, however, has long remained a challenge for larger-scale projects and real-world manufacturability. This work seeks an improved understanding of graphene sheet growth via computational modeling, with the objective of maximizing grain size. To this end, the kinetic Monte Carlo method is used to simulate chemical vapor deposition under various configurations of carbon flow and graphene seeding. Ultimately, both quantitative and qualitative results are obtained to shed light on graphene growth mechanisms, with insights into real-world synthesis and future computational models.

Graphene Synthesis: Method, Exfoliation Mechanism and Large-Scale Production

Graphene is a unique attractive material owing to its characteristic structure and excellent properties. To improve the preparation efficiency of graphene, reduce defects and costs, and meet the growing market demand, it is crucial to explore the improved and innovative production methods and process for graphene. This review summarizes recent advanced graphene synthesis methods including “bottom-up” and “top-down” processes, and their influence on the structure, cost, and preparation efficiency of graphene, as well as its peeling mechanism. The viability and practicality of preparing graphene using polymers peeling flake graphite or graphite filling polymer was discussed. Based on the comparative study, it is potential to mass produce graphene with large size and high quality using the viscoelasticity of polymers and their affinity to the graphite surface.

Theoretical Prediction of CHn Crystal Structures under High Pressures

CHn is the precursor unit for graphene synthesis. We have theoretically predicated a series of CHn structures with n = 1, 2, 4, 6, 8, 10, and 12 at elevated pressures (ambient pressure, 50, 100, 200, 300, 350, and 400 GPa) using evolutionary algorithms. The predicted CH and CH2 structures are graphane-type and polyethylene over the whole considered pressure range, respectively. The molecular crystalline methane is predicted for the stoichiometry of CH4. The combination of methane and H2 for CH6, CH8, CH10, and CH12 up to 300 GPa are obtained. At 400 GPa, the mixture of polymer and H2 for CH6, CH10, and CH12 comes into play. From the computed enthalpy, higher pressure and more hydrogen concentration contributed to the decomposition (to carbon and H2) of CHn systems. The total density of states for these CHn structures show that only the CH12 phase is metallic above 300 GPa. The rotational properties are traced in H2 and the CHn structures. The CH4 rotation is more sensitive to the pressure. The H2 units are nearly freely rotational. Other structures of CHn, including fcc-type and experimentally known structures, are not competitive with the structures predicted by evolutionary algorithms under high pressure region. Our results suggest that the CHn (n > 4) system is a potential candidate for hydrogen storage where H2 could be released by controlling the pressure.

Graphene Synthesis and Its Recent Advances in Applications—A Review

Owing to the remarkable chemical and physical properties, graphene has been widely investigated by researchers over the last 15 years. This review summarizes major synthetic methods such as mechanical exfoliation, liquid phase exfoliation, unzipping of carbon nanotube, oxidation-reduction, arc discharge, chemical vapor deposition, and epitaxial growth of graphene in silicon carbide. Recent advances in the application of graphene in graphene-based lithium ion batteries, supercapacitors, electrochemical sensors, transparent electrodes and environmental based remedies are discussed.

Spectral study of argon-methane mixture plasma jet generated by a DC plasmatron

We present the results of studying optical emission spectra of Ar:CH4 plasma produced on a DC plasmatron for graphene synthesis. We have identified the basic set of spectral lines and bands in the obtained spectra and shown that H lines and C2 bands appear due to direct excitation by an electron strike of corresponding neutral particles. C2 molecular bands were also identified in the spectra with intensity considerably lower compared to previous studies where He: C2H2 mixture was used as plasma-forming gas.

Risk analysis and solution of using graphene: Material, synthesis, and application (Mini review)

Graphene is a nanomaterial with unique physical and chemical properties. The two-dimensional hexagonal sp2 structure in the honeycomb lattice has high thermal conductivity, high electricity, mechanical strength, and large surface area. The nano properties are significantly different from the bulk material. The review of the material, synthesis and application aspects of graphene gave rise to risk analysis in each field of study. Graphene material does not yet have adequate information regarding the risk of danger. Because graphene is nano-sized, this material can enter the human body through inhalation, ocular, cutaneous and oral. Graphene synthesis involves using chemicals that will produce hazardous products and reduce agents with high toxicity. The risk becomes more and more when the challenges of mass production of graphene are faced. Graphene can be applied as sensors, nanoelectronics, and biomedical applications. In this biomedical application, graphene has direct contact with humans and can increase reactive oxygen species in the body. The recommendation to overcome the risk is to use personal protective equipment and handle graphene material properly. The toxic materials involve in the synthesis step can be replaced with other environmentally friendly materials. Antidotes substances can reduce the toxicity of graphene materials so that the risks graphene in its application can be overcome.

Comparing the methods of copper substrate polishing for CVD graphene synthesis

This paper presents a comparison of chemical and plasma electrolyte polishing methods for preparing a copper substrate for graphene synthesis by chemical vapour deposition. It is shown that in order to achieve the most uniform morphology of the surface of the copper substrate, it is preferable to use the electrolyte-plasma polishing method. With its help, the proportion of multilayer regions in the graphene coating obtained as a result of CVD synthesis decreases. The obtained results may serve a recommendation for creating a graphene coating with specified parameters.

IMPACT OF THE GRAPHENE SYNTHESIS AND CONCENTRATION CONDITIONS ON ELECTRICAL PARAMETERS OF GRAPHENE — GRAPHITE SYSTEM

Electrochemical impedance spectroscopy was used to study the electrical parameters of graphite-graphene systems with different mass concentrations of graphene. Graphene was synthesized using two methods of plasma arc discharge from aqueous and non-aqueous medium (water and liquid nitrogen) to determine the impact of graphite concentration, water, and heat treatment of graphene on electrical parameters (conductivity and electrostatic capacity) of the graphite-graphene mixture. The average va­lues ​​of active resistance and electrostatic capacity of these systems are obtained. The optimal ratio of components with high capacitance and conductivity, which was 1: 1. The influence of heat treatment adsorbed on the graphene surface of the water and mass fraction of graphite on the change of electrical parameters of the system is shown. Comparison of the values ​​of capacity and active resistance of the samples showed that the presence of water in graphene reduces the average values ​​of capacity relative to graphene without water by 10 times and symbolically increases the active resistance at a mass ratio of graphene to graphite 1: 3, and at a ratio of 1: 1 values ​​are proportional. Comparison of resistance, capacitance, and charge distribution calculations in a graphite-graphene mixture in the frequency range 10–2 ÷ 103 Hz established the effect of heat treatment on increasing the values ​​of capacitance and active resistance. Heat treatment at 2500C of graphene, synthesized from an aqueous medium, leads to an increase in the values ​​of capacitance and conductivity, which occurs due to a different distribution of charges on the surface. Analysis of charge distribution maps shows that water adsorbed on the surface of graphene in the presence of a signi­ficant amount of graphite can be a factor in interfering with the distribution of charge carriers and significantly reduce the conductivity and electrostatic capacity of the system.