Graphene grown by Chemical Vapor Deposition has many uses, but for most applications must be transferred from the metal catalyst to a different substrate. In this guide, we will explain the two most popular methods for transferring graphene from a metal catalyst to a substrate -- using thermal release tape and the PMMA method.
The first method for graphene transfer is by using thermal release tape. This method results in low-residue graphene, but it is highly unlikely to result in continuous coverage.
The second method is the PMMA method. This method uses Poly(methyl methacrylate) (PMMA) to transfer graphene to a substrate. It results in continuous graphene with mild residue due to the PMMA. Since continuous graphene in often a requirement, the PMMA method is usually preferable.
Transfer using graphene transfer tape
Transferring graphene using our thermal release tape is not a difficult task. By following the steps below, you should be able to transfer your graphene onto the substrate of your choosing. Please keep in mind that graphene transferred using our graphene transfer tape is unlikely to be continuous. If continuous graphene is a requirement, the PMMA method is your best option. In this case, please consider purchasing graphene transferred at our laboratory for best results. You may contact us at info@graphene-supermarket.com if you need assistance with your selection.
When transferring graphene using thermal release tape, first peel off the protective layer from the thermal release tape, then put the adhesive layer of the tape on top of the layer of graphene. Apply firm pressure to the tape with a rubber roll or a spatula.
Note: If you are transferring graphene from a catalyst deposited onto a silicon wafer, soak the wafer in water and then peel the tape from the wafer. The layer of the metal catalyst should take off from the water and cover the tape uniformly.
The metal catalyst should then be etched away. First, prepare the etchant. We recommend using 1M solution of ferric chloride (FeCl3) in water. This solution works well for copper as well as for nickel. Then, warm the etchant to 55-65ºC. The etching takes an estimated 5 minutes for nickel and 25 minutes for 25 µm copper foil. Then leave the tape in the etchant for another 5 minutes after the metal visibly disappears to remove microscopic metal pieces.
The adhesion of the surface of the target substrate to graphene plays an important role in successful graphene transfer. It is crucial to keep the surface of SiO2 clean. We recommend sonicating the samples in RCA SC1 solution (NH4OH 28%: H2O2 30%: H2O = 1: 1: 5) at 55ºC for at least 15 minutes. We have also found that treating the target substrate with oxygen plasma for 15 minutes helps to improve the adhesion of the graphene. Keep in mind that the transfer should be done within a few minutes of the plasma treatment.
It is easy to check if the cleaning and the plasma treatments have been done properly. The substrate becomes very hydrophilic; a drop of DI water deposited on the substrate spreads instantly across the surface.
The tape with graphene should be pressed firmly to the substrate – avoid damaging the substrate. The substrate must then be heated to about 100ºC, in which case the tape will lose its adhesion and the graphene film will detach from the tape and transfer to the substrate.
Keep in mind that it is very difficult to obtain continuous graphene coverage when thermal release tape is used for the transfer.
Transfer using PMMA
If continuous graphene is a requirement for your experiment, we would recommend using the PMMA transfer method. This method is more complicated, but gives almost continuous coverage.
Using this method, a layer of PMMA is spin-coated onto the graphene to act as a support. An etchant is then used to remove the metal catalyst, after which the PMMA/graphene stack is transferred to another substrate. Solvents are then used to remove the PMMA, completing the graphene transfer1.
Transferring graphene using the PMMA method is not a simple procedure, and requires advanced knowledge including wet chemistry. On our website, you can find numerous products which are transferred on various substrates – this includes SiO2 wafers, glass, quartz, and PET – using the PMMA method.
We also have the ability to transfer graphene onto your custom substrate using the PMMA method at our facilities. If your project requires PMMA transfer to your custom substrates, please email us at info@graphene-supermarket.com.
If you believe that the PMMA method may be more suitable for your purposes, but would like to do so yourself, please refer to the following papers:
1) Toward Clean and Crackless Transfer of Graphene Liang et.al.,ACS Nano, 2011, 5 (11), pp 9144–9153
2) Transfer of Large-Area Graphene Films for High-Performance Transparent Conductive Electrodes, Li et.al., Nano Lett., 2009, 9 (12), pp 4359–4363