Spectroscopy of carbon: from diamond to nitride films

Every surface scientist knows about the importance of carbon spectroscopy: the signals of C 1?s and C KLL usually are indicating the surface cleanness, whereas C 1?s peak is often used as a reference for the calibration of energy scale. Carbon spectroscopy becomes even more important in the case of the studies dedicated to new carbon-based materials, such as nanotubes, graphene, diamond-like carbon (DLC), carbon nitride, carbides, etc. It is well-known that the carbon atoms can be arranged in a great variety of crystalline and disordered structures, because their electrons can hybridize in sp3, sp2 and even in linear sp configurations. Namely, the hybridization of carbon electrons defines the mechanical, electrical and optical properties of these materials. Indeed, between the pure diamond (sp3) and graphite (sp2), there are many phases of amorphous material characterized by different sp2/sp3 ratios and generally named DLC. Electron spectroscopies (X-ray photoelectron spectroscopy, Auger electron spectroscopy and electron energy loss spectroscopy) are widely recognized as analytical techniques, able to identify the bonds of diamond, graphite and amorphous phases of carbon. The binding energy of C 1?s spectrum together with its plasmon losses, the shape of Auger peak and valence band spectra can be used to characterize the structure of carbon-based materials. In this study, an overview is reported on carbon spectroscopy, comparing different experimental methods. Their application for the characterization of DLC and carbon nitride films, including the determination of carbon's sp2/sp3 ratio is discussed and illustrated by experimental results obtained for a series of thin films of these materials.