It's probable sonication may have broken the nanotubes, but it sounds strange to me that you can obtain graphene sheets from the process.

Autually, I don't know exactly what they are. I just guess they are graphene sheets. Please see the AFM image.

your AFM image should be improved!

I am sorry I have no experience with AFM, so I can't help much more here. The only thing is that obtaining graphene from a sonication process is something I have never heard of. It's much more probable they are bundles.

Do you have some suggestions on the improvement of this AFM images. I was using 4-12 N/m cantiliver.

How can we explain the increased amount of defects? Where do those carbon atoms from CNT go?

Defects can arise after sonication as it is basically mechanical vibrations where liquid bubbles hitting your CNTs. I guess the defect is not much. What is the before and after Id/Ig ratio ?

But producing graphene seems a bit difficult to me. Also, yiu may get a better AFM image for conclusion.

Why don't you repeat your experiment and do before and after SEM/ TEM (if possible)

The ratio of Id/Ig changed from 6% to 15% after ultrasonic bath. Compared to SEM/TEM, AFM is more accessible for me. I plan to do SEM/TEM image after I see the tubes in AFM.

I think this change is may be acceptable after ultrasonication. I have a question, what change have you seen in 2D or G' peak in Raman before and after sonication in terms of intensity and FWHM ?

This might give you a clue whether graphene is formed or not.

Yes! ultrasonication may cut long carbon nano-tubes into shorter tubes. But making graphene sheets out of this technique sounds difficult to me. Raman analysis would help you to distinguish the CNTs and your prepared small graphene pieces. Best of luck for your NEW graphene synthesis method.

Ultrasonic bath usually introduces usually only small energy. What is your starting material? Usually this is very complex. Not sure whether the changes in Raman can be associated with a well defined change.

Thanks a lot for erveryone's help! I attached my Raman spectra in order to improve our discussion. I first say to Rajib Kar. Both the intensity and FWHM of G' peak don't change. Based on it, I think there is no Graphene formation in my case.

Hi Joshua Cardiel! I put my CNTs in the ultrasonic bath for 30 mins. Could you show your images of CTN-bundles after 15 minutes of sonication? As you can see from my Raman spectra, there are tiny blue shifts for D, G and G' peak. Do you think it means my CNTs has been shortened by ultrasonication. Besides blue shifts, the G band becomes narrower, indicating the structures of CNT become purer after ultrasonication and SDS encapsulation.

Hi Anastasiia Mikhalchan! Thanks for those two links! They are really helpful for me.

Hi, Titus Sobisch! The purity of my starting materials can be seen in my Raman spectra labeled with "OrignialSWCNT". It is a mixture of metallic and semiconducting single-wall carbon nanotubes. Its purity is 90wt% given by the manufacturer.

Hi Yin, thanks for the spectrum. Yes no graphene formation but certainly defects have been introduced. More importantly your RBM seem to be a little effected (or is this because of background correction ??). Also for SWCNT, you can deconvolute your G peak as G+ and G-. I think there is also some minor changes. Though I am not too sure. All the best.

Hi Rajib! Those high RBM peaks were not caused by the correction. The deconvolution results show that G band can be split into 1576 cm-1 (G+) and 1554 cm-1 (G-), 1576cm-1 (G+) and1561cm-1 (G-) ,in case of original SWCNT and SWCNT after ultrasonic bath, respectively. The max height of G- peak decreased from 35% to 27% after ultrasonication.

Hi,

Did you figure out what is the white spot on your AFM image? I also had the same problems. I sonicated the CNT for 20s with microtip, and then there are so many white spot in the AFM image. The manufacture said the purity is >90%. I thought it's probably impurities, like amorphous carbon. But there are more these white dots than CNTs.

I have the similar opinion to yours. You can't completely trust the purity value provided by the manufacturer. Perhaps after purification of the CNTs by using air and acid oxidation method, you would get nicer AFM images. I have compared the IR spectra of as-received CNTs with that of purified CNTs. After purification, the absorption peaks are much clear in the range of 1700-1000 cm-1. And the reduction of noise level is considerable.

That's too bad, if those are impurities. Because the amount of impurities seem to be more than CNTs. It's difficult to find CNTs in AFM after sonication😞 Thanks for your reply

Dear Wenwen,

I wonder if their might be an effect of air micro bubbles released during sonication, forcing the CNT's apart. Than after longer sonication the air maybe released and the spacing between the CNT's may get narrower over time.

Just a speculation.

Thanks Titus. I plan to do SEM or TEM to check what are those white stuff.

Hi, wenwen! What did you find in your SEM measurement?

Hi Yin,

Most of the CNTs are at the edge of the silicon wafer. In the middle of the silicon wafer, most are some small aggregate or some impurities. When I take the AFM image I choose the middle and looks clean area, so there are many “white spots”.

I am curious about the origin of those impurities. They could come from as-received CNTs or be produced by sonication process. Have you purified your CNTs before sonication?

No, I didn't purify. I guess they come from the received CNTs. Because I sonicated for a short time and the impuritities looks like amorphous carbon not shortened CNTs.

You can simply perform a TGA measurement to make sure whether amorphous carbon is present in your raw material.

http://pubs.acs.org/doi/abs/10.1021/ja906267g

Thanks Yin.

The spots are probably metal fragments from the sonicator.