Hello everybody,
I have a sample with graphene on top made by mechanical exfoliation over a SiO2 300 nm/Si substrate. There are some interesting flakes on it but the surface seems to have some dust or dirtiness on top that I would like to remove if possible in order to continue working with it. Is there any procedure that I can follow in order to clean it not damaging the graphene?
Please, find attached a picture obtained with the optical microscope (x100, 0.95 NA) of one of the flakes and the corresponding AFM image of one of the borders.
Hi, Elisa, I can recommend you the procedure that I follow to clean ME graphene. Along with the airborne impurities, the surface also has impurities ( high molecular weight polymer) from the scotch tape. I recommend you for the ultrasonic bath treatment first in ethanol (HPLC grade) for 10 minutes and then for acetone (HPLC grade) for 10 minutes. It is to dissolve polar and non-polar impurities respectively in solvents. Prolong sonication or using high power can fold graphene edges. Finally heat treatment in nitrogen or argon atmosphere 100 to 200-degree centigrade. It is hard to remove polymer residue from the scotch tape, but certainly, you will get a suitable surface for the AFM operation.
Hi Elisa, If the contamination is just dust/airborne dirt i would remove this with a N2 gun. From your AFM it looks like polmer residues as Manoj suggest. Ultra-sonication in Acetone/NMP would remove this but could result in your flakes curling up or detaching from the substrate. Therefore i would:
1) Leave samples in hot acetone for 1 or 2 hours.
2) Without drying, transfer samples to fresh acetone for 12 hours / overnight.
3) Rinse in Isopropanol / Ethanol and dry with N2 gun.
4) Anneal in forming gas H2/Ar at 300-400C for 2 hours.
If this doesn't remove the residues then it is unlikely any further chemical or thermal treatment will.
Hi Elisa, I would recommend, if possible, to avoid/minimise the amount of chemical cleaning and go for annealing at temperatures around 300-400 degC in forming gas for at least 1 hour (if you use rapid thermal annealing, 3 minutes or so). If anything, but brief rinsing in acetone/isopropanol prior to annealing.
Depending on the application you are targeting and graphene quality and its interface with substrate, as you may know, it would be better to allocate some time to study the best cleaning method.
Thank you all for your kind answers! I have more than one sample with the same conditions of dirtiness so I have the opportunity to try all the cleaning methods proposed here, and then compare its effectiveness.
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