Dear Seo,

- Since you almost have it upto last steps, I would try more times to make the step 7 work, or add new steps: I would get another fully cleaned substrate (cleaning the substrate very well will highly increase the adhesion), and make a sandwich (e.g. press the second substrate on the top of the graphene-holding substrate). Then, I would not rinse it with IPA. I would create a simple apparatus to just slowly hold it on the IPA, perhaps a little more time to wash it out. Then, I would slowly open the sandwich, and take SEMs or even search under an optical microscope to see if I'd observe any left graphene on any of the two substrates.

- This experiment is difficult, and is skill required, and is supposed to be difficult, and that's perhaps why the price per substrate is ~$1000.

- There has to be and are other methods to do that, which I'm not sure for what applications you are interested to use, or what your overall goal would be.

- There are several top researchers in this particular domain in KIST and SKKU, such as Sukang Bae, that you may check out with them:

https://www.nature.com/articles/nnano.2010.132

Best,

J.

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https://www.cyberbond1.com/blog/p.150831000/adhesives-for-hard-to-bond-substrates-clean-surfaces-require-surface-treatment/

https://www.microchemicals.com/technical_information/substrate_cleaning_adhesion_photoresist.pdf

https://phys.org/news/2011-09-hot-nickel-nudges-graphene-semiconducting.html

http://gel.skku.edu/

https://www.graphene-info.com/tags/sungkyunkwan-university

http://ajayan.rice.edu/research/graphene/

http://ieeexplore.ieee.org/document/7388665/?reload=true

https://www.researchgate.net/publication/221767768_Wetting_transparency_of_graphene

http://omaxmicroscope.com/omax-40x-2500x-usb3-10mp-infinity-trinocular-metallurgical-microscope-transmitted-reflected-light.html?SID=utud87igftc191eb9oe9nj2477&gclid=CjwKCAiAu4nRBRBKEiwANms5W7G9KOaqD_h1NLZb4qVbZV8ayt2UQuSpw8dQMGBqP_yw-CClzExmGRoC2fcQAvD_BwE

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Try to deposit graphene oxide on the substrate, then make the reduction process on the surface.

I am not absolutely sure, but it seems that, DI in step 7 making the problem. May be ur DI is penetrating beneath Gr and since Gr is hydrophobic and its getting peeled off from SiO2 substrate due to very low adhesion. In our case we never use DI at all. Acetone wash > do not let it dry and start IPA wash (to remove Acetone residues) > do not let it dry and start Ethanol wash (to remove IPA residue) > blow gun drying with filtered N2 gun (Ethanol easily gets evaporated in atm) > hot plate annealing at 150C for 30 min. May be ur use of DI is making the problem.. Try this out and let us know if its better.. good luck..

Chandan Biswas :

I proceeded the method you mentioned, using the ethanol to remove the residue of IPA.

Can I have some questions?

1) I think there is no difference between IPA and ethanol.

Can I know whether there is a difference or not?

2) After proceeding, I could see something like the residue of IPA.

Therefore, I want to know if it is the residue of IPA.

3) I want to know if it is okay to put this sample into the DI after process

you mentioned and annealing.

Thank you for sharing your knowledge.

Hi Seo,

The boiling point of IPA is much higher than Ehanol (EtOH). EtOH easily get evaporated in room temp but IPA not easily, takes much longer time due to increased boiling point. But you should not let EtOH or IPA dry by itself, it will make residue by solute aggregation. Use should use N2 gun to blow EtOH out before it dry out by itself.

But I think this not the point of your problem. Your problem is the adhesion of Gr-SiO2. And thats why Gr is not sticking.

In our case we use 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. The time depends on the Cu foil thickness. For 25 micron Cu foil it takes about 30 min. for 100 micron 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 SiO-Si substrate.

5) Mild N2 gun to remove water between Gr and SiO 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 inclined manner)

8) IPA flow before acetone dry out (both side of the substrate to wash out acetone completely)

9) EtOH flow before IPA dry out (both side of the substrate to wash out IPA completely)

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

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

Try it out.. its very easy and less complicated that what you are using now. In our case our success rate is 100%. Good luck.. Let me know if it worked for you.

Hi. Chandan Biswas.

Thank for your kind very much.

I will try this method and inform the result to you!

Hi. Chandan Biswas.

We are proceeding the process you mentioned.

But, May I have a question?

We will plan to evaporate a metal after graphene transfer.

Therefore, we should need Developer and DI to make PR pattern.

Is it okay to use DI to remove Developer?

I worry about remove of the graphene when I use DI to remove the Developer.

Therefore, Are there any methods to remove developer by not using DI?

Your information gives me much help!

Thank you!

Hi. Chandan Biswas.

I completed the graphene transfer as you mentioned.

The result of this method shows there is not any residue of IPA.

Thank you very much!