Date Published: February 04, 2016
Publisher: John Wiley and Sons Inc.
Author(s): Yi Chen, Xiao‐Lei Gong, Jing‐Gang Gai.
Graphene, the thinnest, strongest, and stiffest material with exceptional thermal conductivity and electron mobility, has increasingly received world‐wide attention in the past few years. These unique properties may lead to novel or improved technologies to address the pressing global challenges in many applications including transparent conducting electrodes, field effect transistors, flexible touch screen, single‐molecule gas detection, desalination, DNA sequencing, osmotic energy production, etc. To realize these applications, it is necessary to transfer graphene films from growth substrate to target substrate with large‐area, clean, and low defect surface, which are crucial to the performances of large‐area graphene devices. This critical review assesses the recent development in transferring large‐area graphene grown on Fe, Ru, Co, Ir, Ni, Pt, Au, Cu, and some nonmetal substrates by using various synthesized methods. Among them, the transfers of the most attention kinds of graphene synthesized on Cu and SiC substrates are discussed emphatically. The advances and the main challenges of each wet and dry transfer method for obtaining the transferred graphene film with large‐area, clean, and low defect surface are also reviewed. Finally, the article concludes the most promising methods and the further prospects of graphene transfer.
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Chemical vapor deposition method is believed to be an efficient method to synthesize LAG. The mechanism of CVD method is described as follows: decompose the hydrocarbon precursors (CH4) at high temperature and then deposit the decomposition products on metal substrate to form single‐layer or few‐layers graphene. Graphene synthesized by CVD method has been realized on many metal substrates, such as Fe,29 Ru,30 Co,31 Ir,32 Ni,24 Pt,33 Au,34 and Cu.23, 35 To transfer graphene grown on these metal substrates, etching of the metals is the efficient and straightforward way. Fe, Ru, Co, Ni, and Cu can be etched by their etchants easily. But, for the chemically insert or noble metal substrates, such as Ir, Pt, and Au, the traditional wetting transfer methods are not available, because these metals are difficult to be etched away completely or the cost is too high. The electrochemical delamination method, which will be discussed later seems to be an efficient way to transfer graphene grown on these metal substrates.
We have discussed the transfer methods of graphene grown on the metal substrates by CVD method in the part 2. CVD method is believed to be an efficient way to synthesis LAG. But the surface of the Cu substrate is rough, so graphene grown on Cu substrate is easy to form wrinkles. Besides, the orientation of the graphene cannot be controlled easily. Epitaxial growth of graphene on SiC surface is also an important way to synthesis LAG. High‐quality graphene can be grown on SiC wafer by self‐limiting sublimation of Si. And the synthesized graphene has a single orientation because of the self‐limiting growth process. SiC substrate is insulated, so in some cases it can be used directly without transfer. But the cost of SiC is very high and sometimes the graphene is needed to be transferred to other substrates. It is also necessary to develop the method for transferring graphene grown on SiC wafer. However, SiC is resisted to the chemical etchants. The traditional wet transfer method is not available here.
The transfer of graphene acts as the bridge between the production and application of graphene. In this work, we have reviewed the transfer methods of graphene grown on metal (mainly on Cu) and SiC substrates. All of these methods are aimed at transferring graphene with clean surface and little defect. Many transfer methods have achieved these goals. The success of the graphene transfer is of great significance for the application of graphene film, making it possible for the industrial scalability application of graphene. The “Roll‐to‐roll” dry transfer method can transfer the graphene film as large as 30 in., so it seems to be the efficient method for industrial application. Other methods also have their own advantages. Some of them are hopeful for the practical industrial application. Despite that, the transfer methods are still need to be optimized to transfer graphene with little defect and large area. There are still many challenges to transfer LAG films. (1) The first challenge is avoiding the crack during the transfer process while achieve large area transfer at the same time. Monolayer graphene itself can be easily cracked during the transfer process without the assisted of the supporting layer. The improper operation during the transfer process can also induce cracks on the graphene. (2) The second challenge is obtaining LAG film with clean surface. The contaminants on the graphene surface are also big problems to be solved because they may act as scattering centers and induce unintentional graphene doping thus affect the graphene property. It is necessary to obtain LAG film with clean surface when fabricate graphene‐based devices. (3) Simplifying the transfer process to reduce the cost is also a main challenge. The cost of the transfer process must be taken into consideration in the practical industrial application. The complex and time‐consuming transfer methods are unsuitable for transferring the LAG film. Besides, both the transfer of graphene and the synthesis methods of graphene are very important for the application of graphene. It is necessary to optimize the methods to product LAG films with high quality. In recent years, the transfer‐free growth methods where graphene grew directly on target substrates have been reported.88, 89, 90, 91 Graphene grown by the “transfer‐free” method can be directly used without further transfer. If these methods can be applied for industrial scalability production of graphene, it will greatly promote the application of graphene. But before these methods become mature, the transfer process still plays a very important role in the application of graphene.