Graphene Transfer

Fabricating graphene molecularly through Chemical Vapor Deposition (CVD) has been highly desirable and popular as it can produce the material with a large surface area. The CVD method involves graphene growth on a metal catalyst and the transfer of that graphene onto different substrates for various application purposes. Transferring the material is quite common and can be done in different ways, such as utilizing a thermal release tape and PMMA. This report will explain both techniques and its ease in transferring graphene.

Introduction

Since the graphene market has been on the rise over the past decade, producing a large, high-quality amount has been a common focus in research. Currently, the Chemical Vapor Deposition (CVD) is the most popular and commonly used method in creating desired quantities of continuous graphene due to its ability to develop the material on large surface areas. The CVD method comprises of a heated furnace while decomposed methane gas reacts with a metal catalyst (i.e. copper) in the chamber.¹ Decomposed methane gas releases the carbon atoms necessary to form graphene and the gaseous reactants from methane and hydrogen gases are deposited onto the substrate. Then, graphene formation begins when there is a reaction on the substrate’s surface.

The next step is to transfer the graphene onto a preferred substrate (i.e. silicon dioxide, PET, plastic) that would best suit a particular application. This phase depends on the properties that would be needed for that application and there are different methods of transferring graphene (i.e. free floating, bubble transfer or mixing different techniques) onto a chosen substrate. Some methods, including the use of a thermal release tape or polymer, depends on the suitability for the graphene transfer and they are relatively easy to use.

Thermal Release Tape

Using a thermal release tape (TRT) is a method that is more suitable for transferring a large area of graphene. The TRT is a unique adhesive tape that enables the mechanical transfer of the surface of a graphene sheet.² After graphene has been formed via CVD, the tape can be placed on top of the graphene layer so that the metal substrate can be etched away. After etching, the adhesive side of the tape containing the graphene can now be pressed firmly onto the desired substrate. Temperatures around 100-110°C will release the tape, revealing the graphene on the surface of the target substrate. The advantage of using a TRT would be the low residue and ease of graphene transfer; however, it is very difficult to obtain a continuous coverage of graphene. If an uninterrupted layer of graphene is required, using a polymer would display much better results.

PMMA

Polymethyl-methacrylate (PMMA) is a polymer support placed on top of graphene after the CVD process is complete. Using a polymer like PMMA is excellent to obtain a continuous amount of graphene. PMMA has a relatively low viscosity, wetting capability, flexibility and dissolubility in various organic solvents.³ The polymer forms covalent bonds with graphene and can transfer the material onto any substrate without damaging its structure. In fact, PMMA is desirable due to its availability, properties and ease of processing. After the polymer is placed onto the graphene, the metal substrate on which graphene has grown needs to be etched to free the PMMA/graphene layer.⁴ Etching allows for the graphene to remain beneath the polymer so that the graphene layer is protected as it is being removed from the substrate. Finally, the graphene can be safely placed onto the new substrate of choice and the PMMA can be removed with an acetone wash.

Figure 1, below, shows an ACS Material Trivial Transfer Graphene™ that alleviates the work necessary for graphene transfer. The graphene structure is protected by a layer of PMMA and is ready to be placed onto another substrate. Then, a simple acetone wash can remove the PMMA layer and the graphene can be applied to the appropriate application. 

Figure 1. ACS Material’s patented Trivial Transfer Graphene™ provides an easy way of transferring a single-layer graphene onto any substrate with the use of PMMA.

Conclusion

Graphene is a highly coveted material with extraordinary properties. After applying the CVD method to obtain graphene, using a thermal release tape or PMMA are just some of the ways to protect the graphene layer before transferring onto other substrates. The tape and polymer are relatively easy to use and is dependent upon whether a continuous coverage is necessary for application purposes. There may be some residue from both transfer options, which can prevent a very clean graphene layer.  However, new developments are constantly being made and research being done to find a better, cleaner way to transfer graphene. Ultimately, both options provide a way to acquire graphene but ACS Material offers graphene with or without PMMA in order to maintain a high-purity CVD graphene. 

ACS Material Products:

• Trivial Transfer Graphene™
  
• CVD Graphene on Cu Foil
• CVD Graphene on Si Substrate
• CVD Graphene on SiO₂ Substrate
• CVD Graphene on PET Substrate
• CVD Graphene on Quartz
• Others

FAQ’s:

Q. What temperature is required for graphene transfer?

A. During the graphene transfer, most of the steps are done at room temperature with mild temperatures ranging from 100-110°C, to ensure good stickiness to the target substrate to support the transfer process. 

Q. How does the graphene transfer process work?

A. This process moves graphene from the surface where it’s made to another surface where it will be used. Additionally, this process includes adding a protective layer, removing the metal underneath, and carefully placing the graphene onto a new surface. 

Q. In what ways is graphene used in recent times?

A. Graphene is used in various industries due to its incredible benefits, like exceptional strength, flexibility, transparency, and lightweight. These qualities make it an option for the electronics, biomedicine, and energy storage industries.  

Q. What is the dry transfer technique?

A. The dry transfer technique is moving graphene without any liquids; instead, scientists use materials like PDMS (polydimethylsiloxane) to pick and place graphene cleanly. This transfer can reduce wrinkles and contamination as well.  

Q. What is a wet transfer?

A. The wet transfer techniques use polymers and liquids (like PMMA) to move graphene from one metal to another surface. The metal is etched away in a chemical solution, and the graphene film is placed on a new substrate. 

Q. What are rub-on transfers called?

A. The rub transfer is a method for graphene transfer, a rubbing technique that used to transfer the graphene onto the substrate. It involves rubbing or pressing the printed layer onto another surface with pressure. 

Q. What are the different transfer techniques?

A.The main graphene transfer techniques are dry, wet, and electrochemical transfers. However, the most commonly used method for graphene transfer is the PMMA-assisted wet-transfer method. 

Q. What is the transfer matrix method of graphene?

A. The transfer matrix method is a mathematical approach that is used to study how light or electrons pass through graphene layers. Basically, it ensures the easy understanding of the electronic and optical behaviors of graphene films.

Q.What is the electron transfer of graphene?

A.The electron transfer of graphene is about how electrons move freely and quickly to the carbon atoms. It shows that graphene is an excellent conductor for electronic devices.

References

1. Sharma, Kal R. Graphene nanomaterials. New York, Momentum Press, 2014.

2. Szunerits, Sabine, et al. “Recent advances in the development of graphene-Based surface plasmon resonance (SPR) interfaces.” Analytical and Bioanalytical Chemistry, vol. 405, no. 5, 2013, pp. 1435–1443., doi:10.1007/s00216-012-6624-0.

3. Chen, Yi, et al. “Progress and Challenges in Transfer of Large-Area Graphene Films.” Advanced Science, vol. 3, no. 8, 4 Feb. 2016, doi:10.1002/advs.201500343.

4. Kang, Junmo, et al. “Graphene transfer: key for applications.” Nanoscale, vol. 4, no. 18, 2012, p. 5527., doi:10.1039/c2nr31317k.