Growth Of Graphene Domains Research Articles

Low temperature preparation of the monolayer-graphene/diamond heterostructure with superior mechanical properties

There is increasing interest in the preparation of graphene-on-diamond (GOD) hybrids since it is expected to reveal a new horizon of mechanical applications if the beneficial properties of diamond and graphene are effectively combined. Herein, we demonstrated the atomistic scale events leading to the growth of graphene domains on the diamond during the annealing of the nickel catalyst and diamond substrate by combining experiments and theoretical calculations, including the mechanism transition from high-to low-temperature. Concurrently, the high-quality heterostructure of monolayer graphene on diamond was prepared at a low temperature (760 °C) by rapid thermal annealing technique under the guidance of theoretical insights, and an extraordinarily low coefficient of friction (0.021) was exhibited, representing a 91.1 % reduction against the pristine diamond. The adhesion tests confirmed that such an excellent self-lubricity benefited from the adhesion shield effect of as-grown graphene and the consequent reduction in adhesion energy. Furthermore, the corresponding hardness and elastic modulus were also improved by 14.1 % and 32.5 %, respectively. This investigation presents a great potential of the preparation/integration and application of the GOD heterostructure.

Dynamics of carbon diffusion and segregation through nickel catalyst, investigated by in-situ XPS, during the growth of nitrogen-doped graphene

The mechanisms of diffusion and segregation of carbon from a solid carbon-based film, through a nickel film catalyst, was investigated using in situ, time- and depth-resolved X-ray photoelectron spectroscopy. The graphene precursor was a carbon nitride amorphous film obtained by pulse laser deposition. Changes in both surface and bulk sensitive carbon components versus annealing time was investigated at temperatures between 200 °C and 500 °C. A model of carbon diffusion/segregation through the nickel film was implemented, enabling the quantitative description of the graphene growth. Carbon diffusion through the nickel film was shown to occur at low temperatures (200–300 °C) and to induce the growth of graphene domains. The fine microstructure and high density of defects in the nickel catalyst film accelerated the transport of carbon, faster than conventional bulk diffusion. At 500 °C, bulk diffusion of carbon occurred, due to the recovering of the nickel grain microstructure. The diffusion/segregation model developed in this study can be used as a support to a better control of the growth and quality of the graphene. Our interpretations are discussed in relation to similar approaches related to graphene growth by chemical vapor deposition.

Growth of U-Shaped Graphene Domains on Copper Foil by Chemical Vapor Deposition.

U-shaped graphene domains have been prepared on a copper substrate by chemical vapor deposition (CVD), which can be precisely tuned for the shape of graphene domains by optimizing the growth parameters. The U-shaped graphene is characterized by using scanning electron microscopy (SEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), and Raman. These show that the U-shaped graphene has a smooth edge, which is beneficial to the seamless stitching of adjacent graphene domains. We also studied the morphology evolution of graphene by varying the flow rate of hydrogen. These findings are more conducive to the study of morphology evolution, nucleation, and growth of graphene domains on the copper substrate.

Chemical Vapor Deposition Growth of Graphene Domains Across the Cu Grain Boundaries

Many aspects in the chemical vapor deposition (CVD) growth of graphene remain unclear such as its behavior near the catalyst grain boundaries. Here we investigate the CVD growth mechanism of graphene across the Cu grain boundaries using unidirectional aligned graphene domains, which simplifies the analysis of both graphene and Cu to a large extent. We found that for a graphene domain grown across the Cu grain boundary, the domain orientation is determined by the Cu grain where the domain nucleation center is located, and the Cu grain boundary will not change the growth behavior for this graphene domain. This growth mechanism is consistent with the Cu-step-attached nucleation and edge-attachment-limited growth mechanism for H-terminated graphene domains and will provide more guidance for the synthesis of high-quality graphene with less domain boundaries.

Graphene oxide layers modified by irradiation with 1.0 MeV Au+ ions

Graphene oxide (GO) foils were modified by irradiation using 1.0 MeV Au+ ions, and their elemental composition before and after the ion irradiation was investigated using Rutherford back‐scattering spectroscopy (RBS). The surface morphology was studied using SEM, and changes in elemental composition and structure of GO in shallow subsurface were characterized by various spectroscopy techniques including X‐ray photoelectron spectroscopy and Raman spectroscopy. Electrical properties were determined using standard 2‐point method. The analyses indicate that the Au irradiation up to 1.0 × 1015 cm−1 results in removal of oxygen functionalities and growth of graphene domains, leading to a surface conductivity increase dependent on the applied ion fluence. The Au irradiation with excessive ion fluencies leads to the amorphization of GO foil structure.

Simulation of the Dynamics of Isothermal Growth of Single-Layer Graphene on a Copper Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

A new kinetic model of isothermal growth of single-layer graphene on a copper catalyst as a result of the chemical vapor deposition of hydrocarbons on it at a low pressure has been developed on the basis of in situ measurements of the growth of graphene in the process of its synthesis. This model defines the synthesis of graphene with regard for the chemisorption and catalytic decomposition of ethylene on the surface of a copper catalyst, the diffusion of carbon atoms in the radial direction to the nucleation centers within the thin melted near-surface copper layer, and the nucleation and autocatalytic growth of graphene domains. It is shown that the time dependence of the rate of growth of a graphene domain has a characteristic asymmetrical bell-like shape. The dependences of the surface area and size of a graphene domain and the rate of its growth on the time at different synthesis temperatures and ethylene concentrations have been obtained. Time characteristics of the growth of graphene domains depending on the parameters of their synthesis were calculated. The results obtained can be used for determining optimum regimes of synthesis of graphene in the process of chemical vapor deposition of hydrocarbons on different catalysts with a low solubility of carbon.

Chemical vapor deposition growth of scalable monolayer polycrystalline graphene films with millimeter-sized domains

The preparation of scalable graphene films has attracted an enormous attention due to its industrial importance for graphene applications. Here we present a synthesis method of high-quality continuous monolayer graphene films with millimeter-sized domains on ordinary Cu substrates using oxygen-assisted chemical vapor deposition. This method demonstrates a significantly improvement to the resultant graphene such as a largely decreased nucleation density from ∼106 to ∼101 nuclei/cm2, an increased average domain size from ∼0.004 to ∼1.5 mm and a film coverage from 64% to 100%. We attributed the success of this growth to the surface layer formed by bonded oxygen in Cu, which provides a higher priority for catalyzing the nucleation and growth of graphene domains.

Rapid growth of angle-confined large-domain graphene bicrystals

In the chemical vapor deposition growth of large-area graphene polycrystalline thin films, the coalescence of randomly oriented graphene domains results in a high density of uncertain grain boundaries (GBs). The structures and properties of various GBs are highly dependent on the misorientation angles between the graphene domains, which can significantly affect the performance of the graphene films and impede their industrial applications. Graphene bicrystals with a specific type of GB can be synthesized via the controllable growth of graphene domains with a predefined lattice orientation. Although the bicrystal has been widely investigated for traditional bulk materials, no successful synthesis strategy has been presented for growing two-dimensional graphene bicrystals. In this study, we demonstrate a simple approach for growing well-aligned large-domain graphene bicrystals with a confined tilt angle of 30° on a facilely recrystallized single-crystal Cu (100) substrate. Control of the density of the GBs with a misorientation angle of 30° was realized via the controllable rapid growth of subcentimeter graphene domains with the assistance of a cooperative catalytic surface-passivation treatment. The large-area production of graphene bicrystals consisting of the sole specific GBs with a tunable density provides a new material platform for fundamental studies and practical applications.

A Parametric Study on the Influence of Synthesis and Transfer Conditions on the Quality of Graphene.

In this paper, a systematic and comprehensive study has been carried out to observe the effect of synthesis and transfer conditions on the quality and uniformity of graphene deposition in an atmospheric pressure chemical vapour deposition set up. It was observed that the quality of graphene was highly affected by the synthesis conditions, such as, synthesis temperature, synthesis duration, methane and hydrogen flow rate ratio and total flow rate during deposition and cooling cycles. The quality of graphene was observed to be significantly improved upon increasing the synthesis temperature while increase in methane and hydrogen flow rates beyond a particular limit resulted into degradation in the quality of graphene. From the comparison of scanning electron microscopy images of graphene grown at different times, it was found that the nucleation and growth of graphene domains strongly depend on the growth time. The process of transfer of monolayer graphene was significantly improved by controlling the PMMA concentration using a modified three step technique. Raman spectroscopy and the high mobility (˜8153 cm2V−1s−1) of graphene after transferred onto a SiO2/Si substrate confirm the high quality of monolayer graphene obtained by the optimizations of synthesis and transfer conditions in this study.

Evolution effects of the copper surface morphology on the nucleation density and growth of graphene domains at different growth pressures

In this work, we study the influence of the surface morphology of the catalytic copper substrate on the nucleation density and the growth rate of graphene domains at low and atmospheric pressure chemical vapor deposition (LPCVD and APCVD) processes. In order to obtain a wide range of initial surface morphology, precisely controlled electropolishing methods were developed to manipulate the roughntreess value of the as-received Cu substrate (RMS=30nm) to ultra-rough (RMS=130nm) and ultra-smooth (RMS=2nm) surfaces. The nucleation and growth of graphene domains show obviously different trends at LPCVD and APCVD conditions. In contrast to APCVD condition, the nucleation density of graphene domains is almost equal in substrates with different initial roughness values at LPCVD condition. We show that this is due to the evolution of the surface morphology of the Cu substrate during the graphene growth steps. By stopping the surface sublimation of copper substrate in a confined space saturated with Cu atoms, the evolution of the Cu surface was impeded. This results in the reduction of the nucleation density of graphene domains up to 24 times in the pre-smoothed Cu substrates at LPCVD condition.

Optimization of CVD parameters for graphene synthesis through design of experiments

The optimization process of the desired size and quality of graphene domains is usually very difficult due to the numerous interdependent parameters in chemical vapor deposition (CVD). Here, the method so‐called “designs of experiments” is applied to estimate the relative importance and value of some of these parameters and their interactions for the CVD growth of graphene on Cu foil using waste plastic as a solid source. We found that the growth temperature, time, rate of heating, and preannealing time of the substrate influence significantly graphene growth. In particular, the growth time and rate of increasing of the carbon source temperature appear as the main factors for the growth of graphene domains, where the manipulation of only these two parameters could dramatically change the size of crystals. Thus, our experiment shows that for synthesis of larger graphene domains using waste plastic not only do the growth parameters of Cu substrate influence graphene growth but also the carbon source rate of heating.

Parametric Investigation of the Isothermal Kinetics of Growth of Graphene on a Nickel Catalyst in the Process of Chemical Vapor Deposition of Hydrocarbons

A kinetic model of isothermal synthesis of multilayer graphene on the surface of a nickel foil in the process of chemical vapor deposition, on it, of hydrocarbons supplied in the pulsed regime is considered. The dependences of the number of graphene layers formed and the time of their growth on the temperature of the process, the concentration of acetylene, and the thickness of the nickel foil were calculated. The regime parameters of the process of chemical vapor deposition, at which single-layer graphene and bi-layer graphene are formed, were determined. The dynamics of growth of graphene domains at chemical-vapor-deposition parameters changing in wide ranges was investigated. It is shown that the time dependences of the rates of growth of single-layer graphene and bi-layer graphene are nonlinear in character and that they are determined by the kinetics of nucleation and growth of graphene and the diffusion flow of carbon atoms in the nickel foil.

Surface Diffusion Directed Growth of Anisotropic Graphene Domains on Different Copper Lattices.

Anisotropic graphene domains are of significant interest since the electronic properties of pristine graphene strongly depend on its size, shape, and edge structures. In this work, considering that the growth of graphene domains is governable by the dynamics of the graphene-substrate interface during growth, we investigated the shape and defects of graphene domains grown on copper lattices with different indices by chemical vapor deposition of methane at either low pressure or atmospheric pressure. Computational modeling identified that the crystallographic orientation of copper strongly influences the shape of the graphene at low pressure, yet does not play a critical role at atmospheric pressure. Moreover, the defects that have been previously observed in the center of four-lobed graphene domains grown under low pressure conditions were demonstrated for the first time to be caused by a lattice mismatch between graphene and the copper substrate.

Effect of Cu substrate roughness on growth of graphene domains at atmospheric pressure

In this paper, the morphologies of copper surface such as roughness and grain boundary were found to have crucial roles in the formation of nucleation seeds of graphene domains. We reduced the number density of graphene domains via polishing the Cu substrate in a chemical mechanical method. Scanning electron microscope and optical microscope images showed that it was preferential to form nucleation seeds along the Cu grain boundary and scratched area of the polished Cu substrate. We demonstrated that a very flat surface morphology of Cu substrate was beneficial for growing hexagonal single-crystal graphene domain which could enhance the homogeneity and electronic transport properties of graphene films.

Continuous graphene films synthesized at low temperatures by introducing coronene as nucleation seeds

In this paper, we systematically studied the effects of coronene as nucleation seeds for graphene synthesis at low temperatures by chemical vapor deposition. Naphthalene was used as a solid carbon source which is capable of producing graphene at temperatures down to 300 °C. The experimental results showed clear evidence that coronene seeds work as preferred nucleation sites, through which the nucleation density and graphene domain size could be modulated. The introduction of the seeds greatly improved the homogeneity of monolayer graphene by suppressing uncontrolled nucleation and multilayer growth of graphene domains. The obtained carrier mobility of graphene fabricated at 400 °C by the seed-assisted process reached ~912 cm(2) V(-1) s(-1), which is considerably higher than that of ~300 cm(2) V(-1) s(-1) measured on graphene prepared without seeding. Besides offering cost advantages for large scale application, the technique proposed in this study may find significant applications in graphene/copper hybrid interconnects and graphene based flexible electronics.

Synthesis and morphology transformation of single-crystal graphene domains based on activated carbon dioxide by chemical vapor deposition

Uniform single-crystal graphene domains were synthesized on copper foils by atmospheric pressure chemical vapor deposition with activated carbon dioxide (CO2). Controlled growth of graphene domains with a shape evolution from hexagonal to round has been achieved by varying the flow rate of CO2. The excess CO2 passivation induced graphene domain morphology transformation was systematically studied. Field-effect transistors were fabricated based on our CO2-derived graphene and their electrical properties were measured both in air and N2. The maximum fitted device mobilities for holes and electrons could achieve up to 3010 and 750 cm2 V−1 s−1, respectively. Our method provides a viable way for the industrial application of graphene derived from CO2 which could be converted to carbon materials.

Structural evolution and growth mechanism of graphene domains on copper foil by ambient pressure chemical vapor deposition

The time-dependent structural evolution of graphene domains on copper foils by ambient pressure chemical vapor deposition (CVD) is studied in detail. The single crystalline graphene domains up to tens of micrometer are obtained, and carbon–copper (C–Cu) alloyed nanoparticles have been firstly founded out to act as intermediates which supply carbon species for the growth of graphene domains. The layer number and size can be adjustable by controlling growth time. On the basis of results, the surface adsorption combined with an epitaxial growth procedure is proposed to explain the growth of graphene on copper under the ambient pressure CVD. Our work presents a significant progress in production of graphene with controlled structure.

Step driven competitive epitaxial and self-limited growth of graphene on copper surface

The existence of surface steps was found to have significant function and influence on the growth of graphene on copper via chemical vapor deposition. The two typical growth modes involved were found to be influenced by the step morphologies on copper surface, which led to our proposed step driven competitive growth mechanism. We also discovered a protective role of graphene in preserving steps on copper surface. Our results showed that wide and high steps promoted epitaxial growth and yielded multilayer graphene domains with regular shape, while dense and low steps favored self-limited growth and led to large-area monolayer graphene films. We have demonstrated that controllable growth of graphene domains of specific shape and large-area continuous graphene films are feasible.