Would you please describe clearly your transfer process step by step? I'm not sure I understand correctly the sentence "Before transferring the graphene onto SiO2/SiO, I use acetone to remove the PMMA layer".

For my process, the first PMMA is coated onto graphene/Cu. The next step is removing Cu using APS solution, and PMMA/graphene is floating onto the water. After transferring onto SiO2/Si, the sample is kept for several hours to dry before using acetone to remove PMMA.

In my experience, graphene could be damaged at the final step if the sample is not dried properly. I recommend drying naturally for at least 7h or you can keep it overnight. In addition, you can clean SiO2/Si with UV-Ozone before transfer if possible.

Tuan Hoang Thanks for your detailed answer. I will try your suggestions.

I'm following the same steps as you. First, I am coating the graphene/Cu layer with PMMA and etching onto FeCl3 solution for a while. And then, I remove solution residues from the PMMA/graphene layer with water. After transferring the PMMA/graphene onto SiO2/Si, I let it float in acetone. But I leave it for a short time to dry before the acetone treatment.

As you said, I will wait longer for it to dry. If it doesn't work, I will look for other ways to remove PMMA with acetone or something else. Maybe the graphene won't be damaged if I try evaporating the acetone.

To etch Cu, I suggest using ammonium persulfate (APS) solution instead of FeCl3 to avoid the doping effect.

Besides, you can add N-methyl-2-pyrrolidone (NMP) to acetone to effectively remove PMMA, the ratio of NMP to acetone should be optimized, from my experience NMP : acetone = (5 : 100) up to (20 : 100) v/v.

Dear Sevim, thanks for posting this very interesting technical question on RG. Apparently you are not the only researcher who is facing this problem. In this context please have a look at the answers given to the following closely related question which has been asked earlier on RG:

How can I remove PMMA (Poly(methyl methacrylate)) residue from graphene surface?

https://www.researchgate.net/post/How-can-I-remove-PMMA-Polymethyl-methacrylate-residue-from-graphene-surface

This question has received 36 answers. I hope this helps. Good luck with your experiments!

Frank T. Edelmann Thanks for your answer.

I think my problem is mainly about the transfer method, but I also found more useful ideas for other steps.

Hi Sevim,

Regarding the transfer method, you may try our steps:

In our case, we use a simple transfer method as follows. We never failed so far.

1) Spin coat the PMMA (C4) on the graphene on Cu foil at 500rpm/5s followed 1500rpm/60s.

2) Etch out Cu foil by floating the sample on Cu etchant soln (CE-100, Transene Company, Inc.) The time depends on the Cu foil thickness. For 25 micron Cu foil, it takes about 30 min. for 100 microns around an hour.

3) Float PMMA/Gr on four different fresh DI one-by-one to wash out Cu etchant residue.

4) Fish-out with target SiO2-Si substrate.

5) Mild N2 gun to remove water between Gr and SiO2 substrate

6) Hot plate dry at 70 C for 30 min

7) Unidirectional Acetone flow on top of the inclined substrate (just hold with a tweezer in an inclined manner)

8) IPA flow after acetone (both sides of the substrate to wash out acetone completely). It is important to start IPA flow before Acetone dry-out on the sample. Otherwise, Atm moisture will affect.

9) EtOH flow after IPA (both sides of the substrate to wash out IPA completely)

10) N2 blowgun dry before EtOH dry out by itself. Dry both sides of the wafer completely

11) Hot plate dry at 70 C for 30 min.

For your case, I strongly suggest not to use FeCl3 for Cu etching. It's not good. There are lots of good Cu etchants that exist in the market.

Try it out.. it is very easy and less complicated than what you are using now. In our case, our success rate is 100%.

Good luck.. Let me know if it worked for you.

Best,

Chandan

Hi Chandan Biswas, thanks for your detailed answer. Are you using this method for single-layer graphene or a few?

I will try all these steps carefully.. Hope it works.

Hi Sevim Alkan,

It works for any number of layers. Personally, we did up to 5 layers CVD-Gr samples.

I am sure you can do it. Try. Be gentle and do everything slowly. With some practice, I am sure you can an expert on this.

Good luck,

Chandan

Chandan Biswas

Does the molecular weight used affect anything on graphene transfer process?

like MW 300 instead of 950

thanks.

Are the samples baking before dipping in acetone?

Renato Beraldo First of all, Gr/PMMA samples should not be dipped in acetone, but simply floated (with the PMMA coated side). Before this process, the SiO2/Gr/PMMA must be heated and well-dried on the substrate, otherwise, the graphene may be damaged.

Yeps!.. Nowadays, Is your process okay ??

Renato Beraldo .. keep trying to get the best result. Even if you do the same process over and over, you may encounter different results.

Hello Chandan Biswas

I keep trying all the steps as you said. Can you suggest another solvent as an alternative to acetone ?

Hi Mohamed Refaey,

MW of what? I can not understand properly.

Hi Sevim Alkan,

There are many solvents that dissolve PMMA, but Acetone is the best one. Others may not be so effective.

1) Acetone

2) Diethyl carbonate (DEC)

3) dimethylformamide (DMF)

4) Chloroform

4) Toluene

6) Dichloromethane

Maybe PMMA is not your problem, something else?

If you share your exact problems in detail, I can help specifically.

If you do not have defects in Graphene, PMMA will not damage your graphene for sure. It leaves residues only. But if your graphene is very much defective then PMMA can peel off chanks of graphene layers during the PMMA removal process. If you explain your specific problem with a few pictures/data, then I could help you more precisely.

Good luck,

Chandan

Chandan Biswas MW of PMMA

I use this PMMA it is in form of pellets and I dissolve it in Toluene.

Is that will work? if yes what is the solution concentration (PMMA/Toluene)?

Hi Chandan Biswas ,

I think the main reason damage of my graphene is the solution that I used to etch Cu. Recently, I have been trying the electrochemical delamination method to delaminate Cu foil from Gr/PMMA layer and also trying alternative solutions to etch copper.

I will share with you more detail about my problem in the next few days (in case I face the same problem).

Thank you.

Dear Mohamed Refaey,

I see. We never tried PMMA-MW lower than 495K. Too low MW will make adhesion problems.

I do not recommend making your own PMMA solution. You need to make sure and optimize many things by yourself then. For example, appropriate solvent for good dispersion, cross-linking, etc. It's too much hasell. For example, Toluene is not a good solvent. Chlorobenzene or Anisole is more appropriate.

Just buy it for a standard company, there are many companies available in the market. I am attaching a datasheet from a standard company below. Buy it and focus on your graphene transfer.

Hope this will provide you with some help.

Good luck,

Chandan

Hi Sevim Alkan,

I see...

We are using the Cu etchant "CE-100" from Transene Company, Inc. (PC COPPER ETCHANT -100) for years. Here is the link https://transene.com/cu-etchant/

It is very effective, reliable, and reproducible. I recommend you to buy from a standard company, there are many companies available in the market. I do not recommend making your own etchant solution. You need to make sure and optimize many things by yourself then. I am attaching a datasheet from a standard company below. Buy it and focus on your graphene transfer.

Hope this will provide you with the needed help.

Good luck.

Chandan

Chandan Biswas Deer Chandan Biswas

Thank you so much for your help and clarification.

Why did you remove PMMA before transferring to Si/Sio2 substrate? Any specific reason or conditions to do so? Usually I remove PMMA (Acetone+IPA, five minutes each) after transferring it to the targeted substrate. Don't forget to bake the substrate at 105 degrees celsius for 5 minutes before starting the PMMA removal process.

Moreover, if you are looking for an even cleaner transfer, please use dichloromethane at 45 degrees celsius, for 2 to 3 mint, before acetone and IPA .