It is almost impossible, but there are several ways to reduce the amount of the PMMA resudues on the surface. Using solvents helps to remove thick layers, but the volume of small islands can be reduced only after ~300 C annealing in Ar+H_2 (10%) flow for several hours. If you have problem with contact resistance then oxigen plasma asher or RIE treatment for a short time can help (the device itself should be protected, obviously). No need to remove PMMA completely if you use CVD graphene, because it does not effect any transport properties, unless you have really high quality CVD graphene. Some people try to use high-T oxigen annealing for graphene membranes and it helps to open contamination free areas. If graphene is in contact with any substrate it does not work. For small suspended two terminal devices current annealing allows to remove contamination completely. There is also a simple mechanical method AFM tip can remove all resist (theoretically without damaging the sample) in a contact mode.

If you need a clean surface you can consider to use PMMA/resist free transfer, but it is hard to see a monolayer on top of water. I have excluded from this message several issues you may or may not have taken into account for instance not completely etched second graphene layer of the back side, bad copper substarate, copper damaged by RIE, bilayer graphene islands, as well as a contaminated SiO_2/Si substrate.

HI, After removing the PMMA using acetone, you can try annealing of the sample in vacuum at around 300 C in the presence of Ar gas for couple of hours. Annealing helps in removing PMMA residues.

Hi...you can either use acetone or chloroform for removing the PMMA. The former is a more common solvent being used by many researchers...a bath temperature of 50-70 degree is recommended followed by annealing (vacuum or atmospheres such as Ar, N2 or H2 at 400 C for 1-2 hrs or RTA at 450C in N2 atm for 10 min) for effective removal

It is almost impossible, but there are several ways to reduce the amount of the PMMA resudues on the surface. Using solvents helps to remove thick layers, but the volume of small islands can be reduced only after ~300 C annealing in Ar+H_2 (10%) flow for several hours. If you have problem with contact resistance then oxigen plasma asher or RIE treatment for a short time can help (the device itself should be protected, obviously). No need to remove PMMA completely if you use CVD graphene, because it does not effect any transport properties, unless you have really high quality CVD graphene. Some people try to use high-T oxigen annealing for graphene membranes and it helps to open contamination free areas. If graphene is in contact with any substrate it does not work. For small suspended two terminal devices current annealing allows to remove contamination completely. There is also a simple mechanical method AFM tip can remove all resist (theoretically without damaging the sample) in a contact mode.

If you need a clean surface you can consider to use PMMA/resist free transfer, but it is hard to see a monolayer on top of water. I have excluded from this message several issues you may or may not have taken into account for instance not completely etched second graphene layer of the back side, bad copper substarate, copper damaged by RIE, bilayer graphene islands, as well as a contaminated SiO_2/Si substrate.

http://www.sciencedirect.com/science/article/pii/S0375960113003617

(http://arxiv.org/abs/1301.4106)

Usually what i have seen with a lot os groups is that they remove the PMMA with Acetone. I also thing the first answer by Balakrishna is also correct that you can remove the PMMA residue with Isopropanol (this would be less corrosive).

I don not know if propalyne carbonate will dissolve the graphene. I suspect it will but would be interested to know for sure. Propalyne carbonate will dissolve many types of PMMA especially if the molecular weight is not too high. Some heat wiill help of course.

Can you anneal it in vacuum?

Very simple method!!! Dissolve your sample in either tolune or acetone for 15 to 30 mins. The PMMA residue will washout very easily..

+1 for Alexander and Andrey

Graphene PMMA and annealing

http://pubs.acs.org/doi/full/10.1021/nl203733r

Graphene mechanical cleaning http://apl.aip.org/resource/1/applab/v100/i7/p073110_s1

Current Annealing

http://digital.csic.es/bitstream/10261/10475/1/APL-2007.pdf

You could also consider other polymers for transferring (e.g PC or PS) or as an intermediate layer between gr and pmma and see what happens.

The quality of solvent used for the resist strip is important. Use HPLC grade for the cleanest strip, I prefer chloroform, tetrahydrofuran may also work but can contain small amounts of degradation products that are difficult to remove. Following the removal of most of the polymer using solvent, high temperature (500 degrees C) cleaning under hydrogen and argon (there are numerous papers detailing this process, one example is here: 10.1021/nl102564d) for about an hour has been shown to produce the highest quality samples. Good luck with your work!

Dear Kasap,

Basically in the wet transfer process of graphene on to Si/SiO2, the challenging task is removing PMMA and metal catalyst particles as much possible.Its quite possible by doing annealing at ~ 400 C in the presence of Ar and (5%) H2 atmosphere for longer durations of time

.

Hi Sibel,

an annealing step works almost perfectly: 400°C in ultra-pure hydrogen gas (8N) for 1 hour will do the job.

If you work with graphene on SiC you will have to deal with intercalation at the edges, which is very useful if done appropriately: http://www.nature.com/ncomms/journal/v3/n7/full/ncomms1955.html?WT.ec_id=NCOMMS-20120717

We did not find a solvent that can remove PMMA completely. We always find small residues in AFM after chemical cleaning.

Maybe the residue on the substrate not completely resulted from PMMA and some of them from the etching copper process. So i think the conventional wetting etching method mingh be responsible for the residue. Then recently developed electrical chemical method should be employed to optimize the whole transferring process.

http://carbon.imr.ac.cn/file/Journal/2012/1330521377791.pdf

Do you cover the PMMA/graphene/SiO2/Si sample with acetone or do you drop small amounts of acetone on the PMMA face and then clean it with DI water to remove it slowly and to try to get rid of PMMA residues? Do you use ultrasound to help removing it or will this damage the graphene layer? Thanks for the help!

@Laura, If you use ultrasound it will damage your Graphene layer . so it is always better to avoid ultrasound after transferring graphene to target substrate

thankQ for all....for giving help..

you can immerse your graphene/SiO2/Si sample in boiled acetone for few minutes, followed by annealing in argon for 1h.

Hello, I just joined your interesting discussion.

Could someone give me any suggestions on how the PMMA smell could be removed from an incubator? I needed to degas PMMA solution and due to the lack of nitrogen tanks in our lab, I put PMMA solution in a hypoxic incubator for 2 hrs. The PMMA solution was in small vials with lightly closed lids. However, after removing my vials from the incubator, the smell of PMMA is still there. This incubator needs to be used for cell culture. Any suggestions on how should I clean it?

Thank you very much.

Essentially you are trying to remove residue of organic solvent in which PMMA was dissolved (not PMMA itself). What about flushing with dry nitrogen until the smell is gone? Also, loads of activated charcoal left for long enough inside your incubator should work. Good luck.

Thank you very much for your answer and your suggestions. We do not have in the lab the activated charcoal, so I need to order it. However, do you think baking soda (sodium bicarbonate) could be used instead as it is known for absorbing smells too?

Thank you.

After transfer onto my substrate I place the substrate-Gr-Pmma Stack into a round bottom flask in an oil bath and heat to 90 degrees C under reflux for 2+ hours. By this point enough pmma is removed for conductivity measurements, however some pmma may still be left on the graphene surface which may effect your results. The remaining pmma may be removed by annealing in an Ar atmosphere at a high temperature (I think I heated to 900 C but I'd recommend doing a quick literature search).

How can I etch PMMA isotropically?

Hi All

Please, can anyone give me an idea on how can I transfer a stack of layers to the flexible substrate without damaging the layers? 

Thanks a lot 

Dear Ms. Kasap

The annealing step is one way to remove organic particles (e.g. PMMA)  from the surface but, you should try the transferring of monolayer CVD-grown graphene on copper foil using the polymer poly(styrene) solution in toluene. In particular, we have seen that the large area graphene flakes are intact after transfering to an appropriate substrate. We also have shown how to avoid problems with remaining copper onto graphene. See below two references that could be interesting for you

https://www.nature.com/nnano/journal/v8/n5/pdf/nnano.2013.63.pdf

http://onlinelibrary.wiley.com/doi/10.1002/celc.201402325/full

Best

In our lab, we dissolve the sample in acetone for 8 hrs followed by ethanol and DI water. After that, the sample is annealed at 250 C for 2 hr in Ar. Hope it helps.

Many times, acetone couldn't remove PMMA completely from the graphene surface. In such a case, you can perform annealing of graphene under low pressure of 1×10-1 Pa/0.75 mTorr at ~350 oC in the presence of Ar for one hour.

Hi all,

Can i use acetone as a etching agent to remove PMMA from PC/PMMA blend prepared using THF solvent

you can try acetone and cyclohexane mixture solution to do it

Unfortunately any method is not possible

To remove the sacrificial layer (PMMA) two methods can be used: -

(a). Solvents: Dip the sacrificial layer/graphene/substrate in acetone for 1h, then into iso-propyl alcohol for another

1h and blow the sample with N2 to dry it.

(b). Thermal treatment: Put the sacrificial layer/graphene/substrate into an oven and heat the sample at 450C in inert

atmosphere for 2h.