The graphene is growth on copper foil, and I directly eatch this copper by ~0.5M ferric chloride. I cut the copper foil as 1 square centimetre pieces. Then put one piece into the solution. After 12 hours later, only the graphene is left. And then, I bail the graphene out(with a little ferric chloride) and wash it in DI water many times. Finally, I transfer the graphene on a Sio2(300nm)/Si subsrate.
I don't know what problem do you encounter. You can add your problem information after your transfer process.
In my view, there are two major issues should been noticed:
1, There is no supporting layer on graphene. graphene layer will be fragmentized when etching copper foil, washing it in DI water.
2, The unwanted graphene on back side of copper foil should been remove before you etch copper foil.
If you have some picture of your sample we can solve your problem effectively.
I don't know what problem do you encounter. You can add your problem information after your transfer process.
In my view, there are two major issues should been noticed:
1, There is no supporting layer on graphene. graphene layer will be fragmentized when etching copper foil, washing it in DI water.
2, The unwanted graphene on back side of copper foil should been remove before you etch copper foil.
If you have some picture of your sample we can solve your problem effectively.
Thanks very much for your answer! This picture is what I got. As you see, the graphene is too dirty to test futher. Indeed, the graphene layer is fragmentized. But we don't care the graphene' continuity or area much mow. Another question is that, does the graphene on the back side of copper foil affect its degree of cleanliness?
Although continuity of graphene is not important to you, I think a supporting layer is necessary. It helps you to wash graphene effectively and you need not to be afraid that clean process is too aggressive.
The step of removing unwanted graphene is important. If copper foil is removed with graphene on back side this unwanted graphene layer will huddle up and adhere to graphene sample. There are two pictures attached here to show the phenomenon.
From your picture I don't figure out why your graphene sample is so dirty. Those sparklet looks like polymer residual but you don't coating polymer layer on graphene. You need to review your transfer process carefully to avoid impurity on your graphene/cu sample and etchant.
This sample is dirty but some simple test should be implemented, such as Raman, AFM, XPS or SEM.
The other source of contamination which we have experinced is Cu itself. The quality of Cu foil can vary even from batch to batch from one supplier. You have to look for the cleanest possible material and anneal it before using for synthesis.
The typical contaminant in this case surprisingly is silicon oxide, I was shocked to see in SEM almost vulcanic erruption of SiOx balls from Cu surface upon annealing.
Dear Li
As Jia commented above, there is no supporting layer on graphene before you etch copper chemically and transfer graphene to your final substrate. A very good method for transferring large area monolayer CVD-grown graphene on copper foil using the polymer poly(styrene) solution in toluene, also we have investigated a method to remove interfacial residual copper onto graphene. Maybe the references below 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
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