Hi there. Has it ever happened to you that you handle nominal SLG and it happens you have like the feeling it is FLG, instead? Ok, AFM is normally measuring higher thinkness, but what about the exact fingerprint in Raman? Anyway, is that true that having CVD graphene does not necessarily mean 1 layer, but also FLG made by CVD exists? Bye
ciao Marco!
If you are not sure, I can help you performing some Raman on your sample, so you can be sure what you really have. And yes, it happened to me many times, having FLG instead SLG.
pls let me know. Cheers
I agree with Antonio, Raman spectroscopy should be used as the benchmark to verify SLG vs FLG.
This is not very intuitive since one would expect to be more precise with AFM rather than with Raman. However, the thickness that you measure in AFM is affected by adlayers, water molecules, and contaminants between your substrate and graphene which result in an overestimation of the graphene thickness making you believe you have FLG while it is truly SGL. Not to mention that the differences in tip-sample interaction also contribute to a misestimation of the true thickness of the layer.
Raman spectroscopy is not free from such artifacts since doping, temperature, defects, strain, and chemical variations would affect the Raman spectra. But in general terms it is more reliable. Look at the 2D band lineshape and the 2D/G ratio that are good indications of the presence of SLG.
this is the answer I wanted to receive; but also would like it to be more quantitative: as everyone says the shape of the band would tell you about possible extra layers (2nd, 3rd etc), but the intensity - in case one has low resolution - is generally not addressed. I know that a ratio around 4 would mean SLG; so, when does 2nd layer appear, when e.g. the ration is only 3? and how many layers when the ratio is 2?
Thanks
It is tricky if you want to base that analysis only on the intensity ratios. Let me explain, the 2D band intensity is not directly affected by defects, but indirectly it is! Also, doping can induce changes in the intensity ratios involving the 2D band. And since doping of SLG and FLG is pretty much unavoidable, then you would have a large dependency of the intensity ratios on the experimental conditions rather than on the number of layers.
That's why the usual way is the peak shape analysis of the 2D band. But if you don't have enough spectral resolution to resolve that peak properly, then I wonder if a combination of peak position analysis and intensity ratios could do the job (of course, provided that you have enough resolution to pinpoint the peak positions).
Another alternative to confirm you have SLG is by measuring the dispersion of the 2D band which should be around 90 cm-1/eV.
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Carbon Materials
- Graphite
- Graphene