I2D/IG is the measure of no. of layer of graphene. Its okay, but check with the shape of 2D band. I mean  to say that confirm it by FWHM and fittin with Lorentzian peak. For reference, you can go through Hao et al, Probing Layer Number and Stacking Order of Few‐Layer Graphene by Raman Spectroscopy. small 2010, 6 (2), 195-200.

May be intercalation is modifying the quality of graphene and resulted with enhanced I2D/IG. But I will suggest to check with shape of 2D.

IG/I2D is helpful in calculating number graphene layers, please refer "Das, A.; Chakraborty, B.; Sood, A. K., Raman Spectroscopy of Graphene on Different Substrates and Influence of Defects. Bull Mater Sci 2008,31, 579-584"

According to your Raman data (I2D/G=2.6; IG/2D=0.4) your CVD graphene is bi-layered. After treating with ammonium salt which may intercalates and causes further exfoliation of bi-layer to monolayer graphene and hence IG/2D=0.11.

I2D/IG is the measure of no. of layer of graphene. Its okay, but check with the shape of 2D band. I mean  to say that confirm it by FWHM and fittin with Lorentzian peak. For reference, you can go through Hao et al, Probing Layer Number and Stacking Order of Few‐Layer Graphene by Raman Spectroscopy. small 2010, 6 (2), 195-200.

May be intercalation is modifying the quality of graphene and resulted with enhanced I2D/IG. But I will suggest to check with shape of 2D.

thank you very much for your answers it is much clearer now I have to fit my result and compare them with the articles.

thank you again

I think  I(2D)/I(G) bigger than one suggests monolayer if it is 9 probably graphene was detached from the Cu substrate. In any case factor 9 is strange. the biggest one I have seen was 6. What is the width of the peak?

yes it is exactly what i have been told that's why I don't understand this result., the width of the 2D peak is 35 for the G peak I find a width of about 22. i have attached the raman spectra that I get.

thank you very much alexandros I used a laser with a wavelength of 514nm. I will check the litterature that you have proposed it is very helpfull. (there is actually a shift from 1600cm-1 to 1580cm-1 in the G band, from my colleague it is a "dedoping" effect because of the lift I am about to do some XPS measurment to check if there is any molecule physisorbed). But I have another question about that : do you use the area of the peaks or the intensity to determine the 2D/G ratio? ( I get a ratio of 9.5 if  I use the area but I find a ratio of 6.5 if I use the Intensity wich seems more likely if we compare with what people get in the litterature).

Hello everyone,

I've read all your responses but I still have one last question. I do know that we are getting single layer graphenes (2D/G well over 2, narrow and symmetrical peaks and those are where they should be). But in some cases we are getting 2D/G in excess of 6 without intercalating anything.

By the way, Ramans are done over SiO2 with a 532 laser set at 5mW.

Thanks in advance.

Such a behaviour is observed in graphene whiskers

probably multilayer structures of  twisted graphene (small angle)

This link is really useful,

http://www.instanano.com/characterization/experimental/raman-graphene/