Characterization of C-based materials: The evaluation of sp2 and sp3 hybrids

Abstract Low temperature, low pressure plasma deposition of carbon is widely used to obtain coatings having peculiar properties. These properties may range from those of graphite to those of diamond which are dependent on the number and the organization of the sp 2 and sp 3 hybrids in the film network. The prevalence of the first or of the second electronic configuration determines the physical, the electrical and the structural properties of the material. So the quantification of the sp 2 and sp 3 hybrids is one of the most important parameter to characterize the C-based materials. Unfortunately this kind of analysis is not straightforward. A common problem is related to the lack of proper references to obtain meaningful estimations of the abundance of the sp 2 and sp 3 hybrids. In this work we demonstrate that Ar + irradiated graphite may be used as a standard. Different doses of Ar + ions were delivered to Highly Oriented Pyrolytic Graphite in order to transform its crystalline structure in disorder. Among the methods commonly used to determine the sp 2 and sp 3 abundance, we evaluated the reliability of those based on X-ray photoemitted Auger KVV, C1s and valence band spectra. The modification of the spectral features under Ar + irradiation affects the various methods to a different extent. This work points out that caution has to be used when C-hybrids are quantified using XPS spectra. In fact all the spectral features are sensitive not only to the atoms' hybridization but also to the kind of bonds formed (dangling or saturated) and to the sample structure (crystalline or amorphous).