I compare the Raman spectra of graphene and peptide-coated graphene. 2D band is blue shifted by 12 cm^-1 after incubation with the peptide while the G band remains unchanged. I assume this could be due to slight doping effect with the adsorption of the peptide on graphene. Could you please share your thought ?
blue shift of 2D band can be observed when thickness/number of layers of graphene decreased. Otherwise increase in second order disorder (overtones of D-band). So peptide absorption alone may not helpful to explain blue shift. Better to focus on what type of solvent/salts used for incubation and how the effect your graphene further.
you may get ans in following link.
Article Formation of Hemoglobin assisted Graphene oxide biocomposite film.
The blue shift of 2D band can be due tu decrease of the number of graphene layers and also to the charge transfer
Could You please tell little more? Is 2D sigle Lorenzian or is the shape is more complicated? If is more complicated than You have bilayer or more graphene layers and then 2D is blueshifted. But G should be also slightly blueshifted. It is also possible that You have quite complicated situation. If there is p doping of material 2D is strongly blueshifted, and G band also slightly blueshifted, but if in the same time there is tensial strain than G band will be returned to basic position and 2D band may not return.
All in all chech the width of 2D band to be sure there is one graphene layer. Than check other possibilities.
I could tell you more if I see the spectra. There are a lot of reasons of the blue shift of 2D mode.
Thank you all for your answers. @Petnikota Shaikshavali, Peptide that I'm using is the graphene/graphite binding peptide dissolved in water.
@ Pawek Ciepielewski, please see attached plot
@ Kacper Grodecki, It's single Lorentzian peak. I have attached plot and the optical image of bare and coated graphene flake. Could you please explain reason behind blue shift and red shift of band due to p and n doping or any online source?
This link is really useful,
http://www.instanano.com/characterization/experimental/raman-graphene/
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