I prepared reduced graphene oxide (RGO) coating on PET substrates. In the coated layers, polymeric surfactants and polyelectrolytes were also deposited to make stable and robust coatings. After treating RGO-coated PET films with nitric acid for a few minutes, I found that the films showed much lower sheet resistance compared with the pristine films. (from 10 kohm/sq to 1 kohm/sq, for examples)
Some studies reported that nitric acid treatment induces p-type doping, which leads to lower sheet resistance of CVD grown, defect-free graphene films.
(http://www.nature.com/nnano/journal/v5/n8/full/nnano.2010.132.html)
In this case (linked above), large shifts of G and 2D bands were observed in Raman spectra. However, I couldn't find any noticeable peak shifts in my samples, even though my samples showed pretty broad G and weak 2D peaks.
Thus, I guess the lowered sheet resistance is due primarily to the removal of polymeric surfactants and polyelectrolytes, mostly on the surface. Especially, the weight portion of the polyelectrolytes is around 30~40 wt %. QCM data (mass change/area) also confirm the mass reduction after nitric acid treatment.
But, I'm still wondering if there must be no doping of RGO. I guess RGO is so defective that Raman spectrum of RGO may not be able to reflect the doping effect by acid treatment.
There are numerous reports on p-type doping of CVD-grown graphene, but I have never seen the studies dealing with p-type doping of RGO prepared by exfoliation and reduction of graphite oxide. I would appreciate if you let me know any reports related to doping (p-type in particular) of RGO using nitric or any strong acid. Also I welcome any comments you may have.
Polycatechols can be used to p dope RGO. check the paper titled
"Environmentally Friendly Synthesis of p-Doped Reduced Graphene Oxide with High Dispersion Stability by Using Red Table Wine"
Let me know if it was helpful
Dear Srikanth, thanks for your help. I wanted to find an evidence of p-doping of RGO. However, I couldn't find a clear evidence such as Raman analysis from the paper you suggested. I guess it is pretty hard to figure out because of many defects of RGO.
There is a way to check for evidence of p or n doping using raman spectra and Kohn anamoly. This relates a subtle change in the lattice vibration due to charge carriers which impact the phonons generated and hence can which can be seen using Raman, not by intensity ratio but by frequency ratios. There is a paper by prof. Dresselhaus (MIT) on this topic in some ACS journal, I just dont remember the title. It deals with the changes in Raman spectra for hole or electron doping of graphene. Good Luck and if you are able to find the paper I would appreciate it if you could forward it to me too. Hope this helps let me know
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