There are various methods to produce graphene materials, such as mechanical exfoliation of graphite, liquid-phase exfoliation and reduction of graphene oxide (GO), each with its own set of advantages and disadvantages. Chemical vapor deposition (CVD) is a method of producing graphene that has attracted much attention in the last decade and despite several shortcomings, is considered a leading approach to manufacture graphene, especially for applications like high-performance electronics and sensors, as it can yield high quality graphene sheets with a low defect count and good uniformity.
The CVD process
Generally speaking, the CVD method is based on gaseous reactants that are deposited on a substrate. The graphene is grown on a metallic surface like Cu, Pt or Ir, after which it can be separated from the metal and transferred to specifically-required substrates. When the gases contact the substrate inside the heated reaction chamber, a reaction occurs that creates a film of material on the substrate. The process can be simply explained as carbon-bearing gases that react at high temperatures (900–1100 °C) in the presence of a metal catalyst, which serves both as a catalyst for the decomposition of the carbon species and as a surface for the nucleation of the graphene lattice.
As was mentioned before, conditions like temperature, pressure, duration of time and many more can have a significant influence on the process and so must be carefully monitored.
Advantages and disadvantages
CVD can yield high quality graphene, with common characteristics that may include high homogeneity, imperviousness, high purity, fine grains, good control over layer number and more. However, CVD also comes with several disadvantages - namely a relatively high price of the equipment, toxic gaseous by-products and, as stated before, it is a rather sensitive process that is easily influenced by parameter changes. It is important to note that while CVD is a rather expensive method compared to other methods to produce lower-quality graphene, it is still probably the best way (to date) to acquire high quality graphene, since other ways to do that are even more expensive or complicated.
In addition, the separation (or exfoliation) of graphene from the substrate is known as challenging and it is tricky to accomplish without damaging the structure of the graphene or affecting the properties of the material. Another harrowing task is the creation of a uniform layer of graphene on a substrate, something that is continuously proving to not be easy at all.
Some approaches were and are still being developed to overcome this issue, like modifying the concentration of gases and incorporating spin coating methods, but this remains a challenge. However, despite these challenges, it is important to note that CVD is widely considered as an important and promising method to produce graphene, which is already in use, and will probably be even more so in the future, once further advancements are made. It is noteworthy that CVD is already a dominant manufacturing route for many other nanomaterials, and will assumably be in extremely common use once progress is made to resolve the issues that are currently hindering its acceptance.
While using the CVD method to produce graphene is definitely one the leading approaches in the world, it is still hindered by the challenges mentioned above. Thus, it is currently mostly limited to relatively small volumes and mainly restricted to R&D and academic uses.
However, graphene sheets produced via CVD methods are used in several applications like sensors, touch screens and heating elements. It is believed that once better answers are found to the questions of price and handling of CVD graphene, many more applications will start to appear.
Looking to buy CVD graphene sheets?
If you are interested in buying CVD graphene sheets, check out the Graphene Catalog that lists various CVD produced graphene sheets from several producers.
The latest CVD graphene news:
China-based Wuxi Graphene Film (owned by Grahope New Materials and The Sixth Element) produces patterned CVD graphene films for heating applications. These films are adopted by several Chinese device makers for different heating products - for example Grahope's graphene eye mask we recently reviewed at Graphene-Info.
The team at Wuxi Graphene Film was kind enough to send a few such films for us to review. These specific films are designed for one of WGF's customers and include a proprietary design which includes a USB connector for easy setup - you just plug these into a USB power source and the films heat up very quickly.
University of Cambridge spin-out company, Paragraf, recently announced that it started producing graphene at up to eight inches (20cm) in diameter, large enough for commercial electronic devices.
Paragraf is producing graphene ‘wafers’ and graphene-based electronic devices, which could be used in transistors, where graphene-based chips could deliver speeds more than ten times faster than silicon chips; and in chemical and electrical sensors, where graphene could increase sensitivity by a factor of more than 30. The company’s first device will reportedly be available in the next few months.
GNM focuses on the R&D of graphene heating technology and the development of graphene products in general. GNM adopts WGF's CVD graphene films in its products - for example in the graphene eye mask we recently reviewed at Graphene-Info.
Graphene and 2D materials producer Grolltex has announced the completion of its recent capacity expansion and released production for 30,000 eight-inch wafer equivalents per year at its CVD monolayer fabrication facility in San Diego, California.
“This is the only commercial CVD monolayer graphene production facility in California and in fact it is the largest capacity plant of its kind in the U.S.”, said CEO, Jeff Draa. “Demand for our electronics grade graphene has never been better. Our production lines are capable of producing single layer graphene or single layer hexagonal Boron Nitride”.
China's Evergrande Real Estate group has invested CNY144 million ($21.4 million USD) in Chongqing Graphene Technology, a CVD graphene producer. Evergrande now holds a 35% stake in Chongqing Graphene Tech (which means that company is valued at $61 million).
Chongqing Graphene Technology produces CVD graphene sheets and the company also offers touch panels and other films that use graphene sheets. The company says its production line can produce up to 3 million sheets per year (but we do not know the size of each sheet).