Carbon, in its many forms may exhibit full sp2 or sp3 hybridisation, or a combination.  Equally it may be bound to O, S, N, metals in different ratios or be present as a carbide phase.  In fact the majority of samples exposed to the atmosphere will have a considerable concentration of carbon contamination ~ 2 nm thick.

Common carbon, C(1s) reference energies:

Adventitious Carbon:  284.8 eV (C-C and C-H bonds).

• Typically there will be some C-O and C=O structure associated (286 – 288 eV), however depending no the nature of the material, this is not always a good reference despite its wide use – for example carbide materials or for aluminium, the carbon is typically around 286 eV.

 

Organic/Polymeric materials  (these are average values – See reference [1]):

• C-C/C-H    ~  285.0 eV
• C-O            ~  286.0 eV
• C=O           ~ 288 – 289 eV
• CF2            ~ 292 eV
• CF3            ~ 293 eV

Inorganic carbon:

• Carbide ~282 – 283.5 eV
• Carbonates ~ 288 – 290 eV

HOPG/Graphite, Diamond, Graphene:

• SP2 carbon ~ 284.0 – 284.5 eV  (HOPG typically seen at 284.5 eV )
• SP3 carbon ~ 284.5 – 285.0 eV

By far the best way of determining sp2/sp3 ratio is by means of the D-value [2].  By recording the carbon x-ray induced Auger peak and taking the maxima and minima from its differential form (figure 1), then the sp2% may be found.

References

[1]  Beamson G, Briggs D. High Resolution XPS of Organic Polymers – The Scienta ESCA 300 Database. John Wiley &  Sons: Chichester, 1992.

[2] J.C. Lascovich and S Scaglione, Appl. Surf. Sci. 78 (1994) 17-24