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Among the graphene materials currently available, graphene films deposited via a bottom-up approach have been demonstrated to be a promising candidate for various applications, with exciting demonstrations in sensors, optoelectronics, flexible thermal heaters, touch panels, and filtering membrane.
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Graphene is currently synthesized by two approaches: top-down and bottom-up.
In bottom-up fabrication, graphene sheets with a large area are grown on a metal substrate such as copper or nickel foil by heating hydrocarbon gases such as methane at around 1000°C. The metal substrate acts as a catalyst, assisting in separating hydrogen from carbon. Carbon atoms then land on the metal substrate and self-assemble to form the graphene layer. This process is called chemical vapor deposition (CVD).
Every individual graphene multilayer sequence is a new material in its own right and the thickness of the graphene layers depends highly on the selection of metal substrate.
Graphene is typically produced through CVD in three steps: (i) CVD synthesis of graphene films on metal foils, (ii) chemical etching of the metal, and (iii) transfer of the graphene films to the desired substrate.
The CVD process can be carried out at low pressure (0.1 Torr) or at ambient pressure, and both have been used in pilot lines for industrial graphene production. To prevent the graphene from breaking during transfer, it is covered with a polymer film removed after the graphene film has been transferred to the target substrate.
Roll-to-roll production is a disciplined approach to mass-producing continuous sheets of graphene. The system is made up of two spools that are linked by a conveyor belt that runs through a large furnace. A long strip of copper foil is unrolled from the first spool and enters the first furnace, where it is heated to an ideal temperature. After heating, copper foil is ready to roll through the second furnace, where a specific ratio of methane and hydrogen gas is pumped, which is deposited onto the heated foil to produce graphene. The graphene is rolled onto the second spool as it exits the furnace.
US-based CVD graphene developer General Graphene Corporation is the world's leading manufacturer and supplier of continuous sheet roll-to-roll graphene at atmospheric pressure. Last year it launched its new Gen3.0 CVD graphene production line. They developed a 20-meter-long roll-to-roll system that can produce single and multilayer graphene at a manufacturing capacity exceeding 100,000 meters square per year.
In 2019 AIXTRON, with the support of Graphene Flagship, announced the launch of Neutron, a new roll-to-roll system capable of depositing large areas of graphene on metal foils under ambient conditions and with an annual production capacity of up to 20,000 square meters.
After graphene growth, it is often desirable to transfer graphene from its original growth substrate onto the desired substrate. The current state of the art is to use an etchant to etch the metal and then wet transfer the graphene to the desired substrate. However, after graphene transfer, wrinkles, cracks, and contamination are observed, degrading the graphene's quality.
As a result, significant progress has been made in research aimed at achieving application quality transfer of defect-free graphene at a low cost.
For example, recently, researchers from the Chalmers University of Technology reported developing a low-cost novel method for transferring graphene on affordable PET lamination foil by using an ordinary office laminator.
However, to meet market demand for large-scale graphene applications, high-quality industrial-scale transfer is important. To achieve this, the roll-to-roll graphene transfer is developed. The process is fast, controllable, avoid chemical contamination of graphene film and can transfer graphene on any flexible substrates.
However, what if it is possible to grow high purity graphene without a transfer process. In this regard, scientists from the UK-based graphene developer company Paragraf recently announced that they had solved the scalability problem by growing CVD graphene directly onto a semiconductor wafer, allowing them to grow high purity graphene without the need for a transfer process.
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Among companies actively engaged in CVD graphene production are General Graphene Corporation and Graphene Laboratories Inc. in USA, Graphenea in Spain and Graphene Square and Charmgraphene in South Korea, Wuxi Graphene Films Ltd, 2D Carbon (Changzhou) Tech. Inc. Ltd, and Chongqing Graphene Technology Co. Ltd in China, BGT Materials Ltd in the UK has been working on large-scale manufacturing of high-quality sheet graphene.
In 2017, Graphenea announced that it would be able to produce 7000 wafers of CVD graphene per year with a wafer size of up to 8 inches.
Graphene Square manufactures graphene films on copper with a size of up to 5 × 5 cm2. They also provide custom-sized graphene films on PET with a surface area of 100 × 100 cm2. Charmgraphene announced they have doubled the speed to two meters per minute and can manufacture in lengths up to one kilometer.
Chongqing Graphene Technology, Wuxi Graphene Films, Changzhou 2D Carbon have announced that their annual production capacities for graphene film on Cu foil are 1 000 000 m2, 100 000 m2, and 150 000 m2, respectively, and all can provide graphene films with sizes of up to 300 × 30 cm2 on Cu foil or PET film.
BGT Materials provides graphene film on various substrates, including Cu, SiO2 and PET with sizes in the range of 1 × 1 to 60 × 762 cm2.
Graphene combines flexibility with conductivity, making it an obvious choice for ITO replacement. Researchers from Queen Mary University in collaboration with Paragraf™, developed the world's first CVD Graphene-OLEDs technology that can replace ITO in electronics devices.
Graphene Kitchen Styler is a new cooking appliance concept developed by Graphene Square Inc. that uses CVD graphene to heat and cook food. The device is completely foldable and is capable of precisely tracking the toasting level of the bread, consuming 50% less energy.
General Graphene Corp. is working on commercializing graphene as a high-performance heating material.
In healthcare, Grapheal, a French company, has developed an innovative graphene-based wearable patch for remote monitoring of chronic wounds. Grolltex is a CVD graphene manufacturer based in the United States has developed a graphene biosensor for the detection of SARS-CoV-2.
The last few years have seen a lot of progress in the controllable synthesis, mass production, and new applications of CVD graphene films towards real commercialization. This would eventually aid in the development of the entire graphene industry.
CVD graphene films have gradually evolved into the major building block of the graphene industry, and this trend is expected to accelerate in the coming years.
Continue reading: A Top-Down Approach To Graphene Synthesis
Zhu, Y., et al. (2018). Mass production and industrial applications of graphene materials. National Science Review, 5(1), 90-101.
Wang, M., et al. (2021). Single-crystal, large-area, fold-free monolayer graphene. Nature, 596(7873), 519-524.
Xu, X., et al. (2017). Ultrafast epitaxial growth of metre-sized single-crystal graphene on industrial Cu foil. Science bulletin, 62(15), 1074-1080.
Li, J., et al. (2022). Wafer-scale single-crystal monolayer graphene grown on sapphire substrate. Nature Materials, 1-8.
General Graphene Corp. (2021) Roll to Roll Graphene Production. [online] generalgraphenecorp.com Available at https://generalgraphenecorp.com/technology/#our-graphene
Charmgraphene (2020) Roll to roll CVD graphene films. [online] http://charmgraphene.com/e-main.php Available at http://charmgraphene.com/bbs/board.php?bo_table=e_gp01_film&wr_id=1
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AIXTRON (2019) Neutron Roll to Roll CVD. [online] aixtron.com Available at https://www.aixtron.com/
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Graphenea (2010). Graphene products. [online] graphenea.com Available at: https://www.graphenea.com
Changzhou 2D Carbon (2014) CVD Graphene on Copper. [online] http://www.cz2dcarbon.com/en/ Available at http://www.cz2dcarbon.com/en/product/2016-5-10/121.html
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Akanksha is a Ph.D. research scholar at the Indian Institute of Technology, Roorkee, India. Her research area broadly includes Graphene synthesis by the chemical vapor deposition technique. Akanksha also likes to write science articles regarding the latest research in 2D materials, especially Graphene, and reads relevant papers to understand what is being claimed and try to present it in a simplified way. Her goal is to help every reader understand Graphene Technology, regardless of whether their background is scientific or non-scientific. She believes that everyone can learn - provided it's taught well.
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