Measurement of the relative abundance of sp2 and sp3 hybridised atoms in carbon based materials by XPS: a critical approach. Part II

Among the methods used to measure the abundance of the sp2 and sp3 hybrids in carbon based materials, in this work we systematically compare those based on X-ray photoelectron spectroscopy in order to understand their power and their limits. Six different methods working on different spectral regions namely the valence band, the C1s core line together with its loss feature and the Auger spectrum, were systematically compared. Differently from part I, here are presented results obtained from Ar+ irradiated highly oriented pyrolytic graphite spectra since irradiation provides deep changes in the graphite structure without any change in the C hybridization. The results point out that some limits seriously affect all the methods based on photoelectron spectra in evaluating the sp2 abundance. A severe problem is the lack of proper reference spectra to obtain meaningful estimations of the sp2 hybrids concentration