Growth of graphene from solid carbon sources

Frank-van der Merwe growth in bilayer graphene

Control of the nucleation and quality of graphene grown by low-pressure chemical vapor deposition with acetylene

Pulsed laser deposition of monolayer and bilayer graphene

High-quality graphene was grown on polycrystalline copper (Cu) foils (1 cm x 1 cm) using hot-filament chemical vapor deposition method. The role of process parameters such as gas flow rates (methane and hydrogen), growth temperatures (filament and substrate) and durations on the growth of graphene was studied. The process parameters were also optimized to grow monolayer, bilayer and multilayer graphene in a controlled manner, and a growth mechanism was deduced from the experimental results. The presence of graphene on Cu foils was confirmed using X-ray photoelectron spectroscopy, microRaman spectroscopy, field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) techniques. FESEM micrographs clearly showed that the graphene starts nucleating as hexagonal islands and later evolves as dendritic lobe-shaped islands with an increase in supersaturation. The TEM images substantiate the growth of monolayer, bilayer and multilayer graphene. The I-2D/I-G ratio = 2 confirmed the presence of the monolayer graphene and the absence of `D' peak in the Raman spectrum indicated the high purity of graphene grown on Cu foils. These results also show that the polycrystalline copper foil morphology has negligible effect on the growth of monolayer graphene.

The use of next-generation graphene requires the control of the number of deposition layers together with its fast synthesis for its use in advanced and miniaturized devices. Here, this article describes a novel technique for the selective growth of a continuous film of a graphene pattern (controlled monolayer/multilayer design) by the chemical vapor deposition (CVD) method on Cu foils modified by different plasma treatments. Ex situ Ar plasma treatment is the preferred treatment for monolayer graphene (I2D/IG = 1.81) synthesis. Bilayer graphene (I2D/IG = 1.05) growth was influenced by applying an additional oxygen plasma treatment, which led to different morphologies and control of the surface-active nature of Cu. The required design was achieved by a photolithography process. Graphene synthesis was performed by a short annealing process (60 s) followed by a single-step short burst of graphene growth (60 s). Relatively high density graphene nuclei with faster graphene growth resulted in monolayer graphene in the Ar plasma-treated area. Ex situ oxygen plasma treatment in selected areas was capable of controlling the amount of graphene nuclei formation, while the kink structure was capable of bolstering the adsorption of a relatively high amount of carbon adatoms, resulting in bilayer graphene.

Chemical vapor deposition is widely utilized to synthesize graphene with controlled properties for many applications. And it is one of the most important methods for the preparation of graphene with high quality in large area. Cu substrate is most commonly used for the preparation of graphene in chemical vapor deposition. As is well known, the properties of graphene are greatly affected by the number of layers. However, the syntheses and mechanisms of bi-layer and multi-layer graphene on Cu substrates are still under debate. And how to make a breakthrough in realizing the controllable syntheses of bi-layer and multi-layer graphene on Cu substrates has become a direction for many researchers. In this work, we report bi-layer and multi-layer graphene on Cu substrates prepared by atmospheric pressure chemical vapor deposition. Firstly, the Cu foil is placed on the quartz slides of the tube furnace and heated to 1000℃ with a rate of 15℃/min. After reaching 1000℃, the Cu foilis annealed for 2 h in a gas mixture of hydrogen (20 sccm) and argon (380 sccm). After that, the graphene growth is carried out at 1000℃ under an 80 sccm gas mixture of argon and ethanol. Then, the samples are cooled down to the room temperature with a rate of 100℃/min in a protection gas of hydrogen and argon, and then taken out of the furnace. The graphene is prepared on the Cu foils and finally transferred onto the SiO2/Si substrates. The quality and number of layers of the as-produced graphene are assessed by field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and optical microscopy. By tuning the graphene growth, the monolayer, bi-layer and multi-layer graphene with higer quality and better continuity are obtained. And the growth times of monolayer, bi-layer, and four-layers graphene are respectively 25, 40, and 60 s. And wefind that the graphene layer will be increased in the process of insulation. The growth mechanisms of bi-layer and multi-layer graphene on copper substrates by atmospheric pressure chemical vapor deposition are also discussed. There will be some indiffusible carbon atoms or radicals near the copper foil surface due to the small molecular diffusion mean free path under normal pressure. We suggeste that the bi-layer and multi-layer graphene grown on copper substrates by atmospheric pressure chemical vapor deposition is dominated by van der Waals epitaxial mechanism. This work provides a reference for improving the quality of chemical vapor deposition monolayer, bi-layer and multi-layer graphene.

Graphene is a promising material for many potential applications, owing to its extraordinary properties. Numerous synthesizing approaches have been developed to realize the promising applications of graphene. However, there is lack of a comprehensive way, which combines the following features, i.e. large-area growth, patterned graphene and fast growth at the same time. Here, we provide an engineering approach to both large-area and patterned graphene at a high rate. The high power and continuous-wave lasers were employed to irradiate solid carbon source coated on nickel surface. The rate of graphene production by laser irradiation exceeds 28.8 cm2/min and the solid carbon source is less hazardous compared to typical gaseous carbon sources used in chemical vapor deposition (CVD). The influence of laser process on graphene fabrication was investigated systematically. Raman analyses, optical images and scanning electron microscopy (SEM) results show that the quality of graphene strongly depends on the laser process parameters, including laser power density and scanning rate. Adjusting the parameters to input the appropriate heat, so that the high quality graphene can be obtained in an optimal condition. The influence of carbon source on graphene growth was also investigated. Ultimately, the penetration and precipitation mechanism of carbon into Ni substrate during the fabrication process were also discussed. This approach may reach the scale large enough for practical applications.

Growth of high-quality wafer-scale graphene on dielectric substrate for high-response ultraviolet photodetector

The preparation of graphene with high quality serves as a prerequisite for its usage. Traditional methods of graphene production, represented by liquid-phase exfoliation and chemical vapor depositi...

Synthesis of high-quality monolayer and bilayer graphene on copper using chemical vapor deposition

Quasi-free-standing monolayer and bilayer graphene growth on homoepitaxial on-axis 4H-SiC(0 0 0 1) layers

In this research, we have investigated the unintended graphene nucleation problem and its damaging effects on monolayer graphene synthesis in low-pressure chemical vapor deposition (LPCVD) process. This problem is the growth of graphene on the copper surface with no carbon feedstock. A new source of undesired carbon species was identified which has not been addressed so far. The hydrogen-rich heating stage was diagnosed as the onset of the unintended nucleation for the first time owing to the determinant catalytic role of hydrogen in this stage. It was found out that this problem leads to uncontrollable growth of multilayer graphene, growth of defective graphene film and also inhibition of the reliable synthesis of monolayer graphene. We managed to grow enhanced-quality monolayer graphene by developing some innovative solutions to the problem containing a general solution based on the hydrogen effects in the heating stage. The results reveal a significant decrease in the unintended nucleation density from ∼2000 to almost zero domains per 100 × 100 μm2 copper area. Furthermore, Raman, HRTEM and SAED analysis confirm the defect-free growth of monolayer graphene after employing the solutions. These findings could pave the way for the reliable synthesis of high-quality monolayer graphene as well as large-sized graphene domains.

Bilayer graphene has attracted wide attention due to its unique band structure and bandgap tunability under specific (Bernal or AB) stacking order. However, it remains challenging to tailor the stacking order and to simultaneously produce large-scale and high-quality bilayer graphene. This work introduces a fast and reliable method of growing high-quality Bernal stacked large-area (>3 in. × 3 in.) bilayer graphene film or trilayer graphene domains (30 μm × 30 μm) using chemical vapor deposition (CVD) on engineered Cu–Ni alloy catalyst films. The AB stacking order is evaluated by Raman spectra, electron diffraction pattern, and dual gate field-effect-transistor (FET) measurements, and a near-perfect AB stacked bilayer graphene coverage (>98%) is obtained. The synthesized bilayer and trilayer graphene with Bernal stacking exhibit electron mobility as high as 3450 cm2/(V·s) and 1500 cm2/(V·s), respectively, indicating comparable quality with respect to exfoliated bilayer and trilayer graphene. The record high (for CVD bilayer graphene) ON to OFF current ratios (up to 15) obtained for a large number (>50) of dual-gated FETs fabricated at random across the large-area bilayer graphene film also corroborates the success of our synthesis technique. Moreover, through catalyst engineering, growth optimization, and element analysis of catalyst, it is shown that achieving surface catalytic graphene growth mode and precise control of surface carbon concentration are key factors determining the growth of high quality and large area Bernal stacked bilayer graphene on Cu–Ni alloy. This discovery can not only open up new vistas for large-scale electronic and photonic device applications of graphene but also facilitate exploration of novel heterostructures formed with emerging beyond graphene two-dimensional atomic crystals.

Monolayer graphene from a green solid precursor

Growing twisted bilayer graphene at small angles