The development of graphene is taking place at a rapid pace. The nanomaterial can produced by many different methods, each of which produces different forms of graphene. These forms have often radically different qualities, which are suited for use in different applications.
This article discusses the different types of graphene, and the suitability of graphene fabrication techniques for various applications. It will also cover the price/quality ratio of the different techniques, which is a key factor in large-scale mass production.
Properties of Graphene
The exotic properties of graphene make it an attractive proposition to develop for use in many different types of device.
Although not all of these devices would exploit the outstanding properties of graphene to their full potential, it is incredible to see the number of applications where the nanomaterial outclasses other standard/incumbent materials, at least on paper.
Some of the properties of graphene are listed in the following table:
|Electron mobility (at room temperature)
||2.5 x 105cm2 V-1 s-1
Moreover, graphene is impermeable to all gases and is capable of sustaining high densities of electric current.
It is worth noting that these values are for very high quality graphene - in practical use, the particular form of graphene used will likely be less performant. Hence, the selection of the most appropriate form and grade of graphene material for the application will be crucial.
Types of Graphene
Liquid Phase and Thermal Exfoliation
Liquid phase and thermal exfoliation both involve splitting up graphite to form graphene flakes - either using chemical solvents or thermal shock.
These methods are very scalable to large-scale production - however, the flakes are usually multilayered, not single layered, and the number of layers can be hard to control. The process can also introduce impurities into the graphene.
It is possible obtain smaller platelets of graphene when carbon nanotubes are used in place of graphite, but this makes the process much more cost- and time-intensive.
Synthesis on Silicon Carbide
Silicon carbide can be used to synthesize graphene layers - when Si atoms are sublimated, the remaining face of the silicon carbide becomes a thin graphite surface. Nowadays, it is possible to control the number of graphene layers and to obtain a very high quality over a wide area.
The high cost of silicon carbide and the requirement for elevated temperatures to achieve the sublimation are the main shortcomings of this process. These factors will perhaps limit graphene made by this method to niche markets, such as metrology resistance standards and high-frequency transistors.
Chemical Vapor Deposition (CVD)
At the moment, CVD is considered to be the best method for fabricating high quality graphene in large quantities. This method involves depositing gaseous carbon atoms on a copper foil, then transferring the graphene film to a wide range of substrates, such as silicon.
The CVD process can be controlled to minimize the amount of defects. Although weak points at grain boundaries, and multi-layer regions are quite common in CVD graphene, they have been shown to have a minimal effect on performance in most cases.
The favorable price/quality ratio makes CVD graphene (Figure 1) suitable for many applications such as flexible/transparent electronics, gas barriers, and anti-corrosion coating.
Figure 1. Quality vs price for different types of graphene
Other Types of Graphene
Other types of graphene are also available, including mechanically exfoliated platelets, and graphene films constructed from the bottom up by molecular assembly, but they have a limited set of applications - mainly due to the fact that they can only produce very small platelets or flakes.
Applications of Graphene
Graphene has great potential in many different fields, including photonics, batteries, flexible and transparent electronics, high-frequency transistors, biotechnology, sensors and metrology.
For most of these applications, CVD graphene is the ideal material in terms of cost and quality. Nevertheless, special fabrication techniques may be required in some specialized cases.
For instance, molecular assembly of graphene is a useful process for creating customized components in nanoelectronics. Liquid phase exfoliation is suitable for fabricating graphene inks or paints for use in printed electronics.
Graphenea is a leading graphene producer for industrial and research needs. Graphenea has developed a leading synthesis and transfer process to obtain high uniformity monolayer graphene films on any substrate.
This information has been sourced, reviewed and adapted from materials provided by Graphenea.
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