Measurement of the relative abundance of sp 2 and sp 3 hybridised atoms in carbon-based materials by XPS: a critical approach. Part II

Abstract

Among the methods used to measure the abundance of the sp 2 and sp 3 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. These methods are applied for the study of highly oriented pyrolytic graphite (HOPG), polycrystalline graphite and diamond. The reliability of the methods was checked by studying the effects of Ar + irradiation of HOPG. In fact, ion irradiation causes deep changes in the graphite structure without affecting the C hybridization. The results point out that some limits seriously affect all the methods based on photoelectron spectra in evaluating the sp 2 abundance. A severe problem is the lack of proper reference spectra to obtain meaningful estimations of the sp 2 hybrids concentration.