I want to know why peaks are shifted in GO, in general if I deconvolute it I used to get peaks at 283.3, 284, 285.7, 287.7. Why I am getting peaks in such wird position? any suggestion for me? I went through different articles found that 284 belong to sp2, 285,7 to sp3, 288 carboxy group. Help in figuring out why I am getting peak at 283.3 and what it may be?
Looks like you need to calibrate the binding energy scale; likely the lowest BE peak should be 284.8 for hydrocarbons. If you used charge neutralisation then this usually shifts peaks a little to lower BE.
You'll get a variety of peaks for C 1s, so looking at graphene is very difficult. The graphene species may be fittable with an assymetric peak, as used for metallic photoelectron peaks, due to the high conductivity of graphene. However, unless your sample was grown in vacuum and never exposed to atmosphere, you will have contamination with hydrocarbons and carbon oxides (single and double bonded usually at ~286 and ~288 eV). There are a tonne of literature on XPS of carbon, and the NIST XPS database will show you a lot of the older ones. The problem is that the graphene signal will likely be sat very close to the hydrocarbon contamination, making peak fitting very difficult. Likewise delineating the different species of the O 1s signal will be difficult.
Suggest you measure a piece of metal along with the GO sample, since you'll find the same contaminants of C-C, C-H, C-O, C=O. Then you can apply your fitting parameters to the GO samples, and hopefully the fit will be insufficient, requiring an extra peak at the right BE for graphene!
#Ben F. Spencer:-- Respected sir, I understand the effect of charge neutralisation but do you think that it led to peak shift of 1ev or more if sample is insulating like in my case (Graphene Oxide).
Secondly, I didn't get your idea of taking XPS on a metal sheet, For metals there will be no charge neutralisation effect which again will lead hydrocarbons peak to be at some different position than the insulator sample.
#Ben F. Spencer:-- Sir, I would like to ask one more question i.e every research group quote 284 or 284.5 as signature of carbon (Sp2). Kindly comment on this in reference to charge neutralization effect as carbon is of conducting nature.
Yes charge neutralisation can lead to effects > 1 eV in BE shifts. You can try for a careful adjustment of the neutralisation parameters where possible to minimise the shifts (by aligning C 1s at ~ 285 eV) but normally this is too time consuming or simply not possible, so the binding energy scale is simply calibrated later.
A metal sample can be used to find the BE positions of the carbon contamination for subtraction / peak fitting of these for your graphene sample. You would calibrate the binding energy scale of the metal sample using a well-known metal peak (e.g. Cu 2p, Au 4f, Ag 3d), but yes if there is a good conductive connection you shouldn't need to calibrate the binding energy scale, but typically it will always need some small adjustment. Check out the NIST database of old XPS literature, the calibration of the BE scale is always reported.
If you look through the XPS literature there is always a spread in BE values reported for different chemical species; and often the error on reported values can be 0.1 or 0.2 eV but can be larger as well. A negative binding energy shift from hydrocarbon (~285 eV) makes sense for graphene since it is like a conducting metallic peak at lower BE to the metal oxide (and 284.5 eV is the well-considered position for graphite). But ultimate numbers are difficult to pin down and can be contraversial! Again, it will easier to compare a C 1s peak where there is no graphene to when there is.
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