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When in X-ray Photoelectron spectroscopy, an Si $2p$ peak is defined or a C $1s$ peak is defined at a certain binding energy, how is it done? I presume it is done from mono-crystalline Si but even in that case the Si peak might not only be experiencing chemical shifts due to the $sp^3$ hybridized bulk state, the case for a C 1s peak I guess would be more complicated due to its allotropic distribution, graphene, CNTs, Fullerenes and Diamonds would in my opinion show separate chemical shifts due to the outer hybridized orbitals being differently hybridized (oriented) and strained (in the case of CNTs, Fullerenes and Graphene since they are all $sp^2$ hybridized). The best way in my opinion to get an idea of the binding energy of the samples, would be to perform the tests in a vacuum tube under very high temperature so that all species are gasseous and are not bonded in any way. I would really like to know how these discrepancies are managed.

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    $\begingroup$ As noted, peak positions have been experimentally determined for a number of clean surfaces of reference materials. In 'real' measurements, chemical shifts are observed. I'm not clear on what your question really is, though. For, say, crystalline silicon, one would expect that there would be a chemical shift relative to mono-atomic gaseous silicon. Further, the absolute binding energy is not that important - it is the differences in the electron energy levels that comes in to play. $\endgroup$
    – Jon Custer
    Commented Sep 7, 2016 at 15:51
  • $\begingroup$ So, my point is that we don't have an absolute binding energy for an $Si 2p$ peak, so the $Si 2p$ peak we see is in bulk $Si$ or in $SiC$, especially true i would guess for $C 1s$ peaks then, since we would not have an absolute $C 1s$ peak , but a $C 1s$ graphene or a $C 1s$ diamond or a $C 1s$ fullerene $\endgroup$
    – Ghosal_C
    Commented Sep 7, 2016 at 18:33
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    $\begingroup$ And that is a strength of XPS - it is sensitive to the chemical environment. $\endgroup$
    – Jon Custer
    Commented Sep 7, 2016 at 18:39

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