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 sp 3 , sp 2 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 (sp 3 ) and graphite (sp 2 ), there are many phases of amorphous material characterized by different sp 2 /sp 3 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 sp 2 /sp 3 ratio is discussed and illustrated by experimental results obtained for a series of thin films of these materials.

In the present work, a detailed spectroscopic investigation of carbon in different crystalline forms from diamond to graphite was carried out. The spectra of photoemission peak, plasmon losses and X-rays-excited C KLL were studied in order to characterize the carbon phase in different samples. In addition, a method for determination of sp 2 /sp 3 ratio from the first derivative of Auger C KLL spectrum was employed. The obtained results indicated that carbon photoemission peak for sp 2 and sp 3 configurations is characterized by the same value of binding energy. The peaks of plasmon losses and Auger KLL transition were more diagnostic than C 1s photoemission peak, permitting to distinguish the sp 2 and sp 3 configurations. For intermediate situation, which is present in diamond-like carbon (DLC), characterized by a mixture of sp 2 and sp 3 states, the spectra were very similar to the carbon-black, whereas single-wall carbon nanotubes (CNT) were containing about 50% sp 2 states.

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Four types of gas sensors based on SnOx thin film with and without additives (Pt and Sb) were investigated by means of x-ray photoelectron spectroscopy and scanning Auger microscopy. The sensors were deposited on Si substrates by using reactive dc magnetron sputtering. The temperature dependencies of the electrical resistivity response to CO gas exposure were measured in order to characterize all types of fabricated sensors. The surface chemical composition before and after various treatments (Ar+ ion sputtering, thermal annealings in ultrahigh vacuum, and oxygen up to 400 °C) was determined from core level and valence band spectra. The three main types of oxygen species were found on the sensors’ surface: oxygen in SnOx, adsorbed hydroxyl groups and adsorbed water. An ultrathin Pt overlayer, which enhances the gas sensitivity in a low operating temperature range, was found to be very porous. The addition of a Pt overlayer was promoting a formation of hydroxyl groups, while the surface oxygen species was independent of the Sb doping. The obtained results support the assumption that the changes of the sensors’ resistivity under reducing gas exposure are caused more by the change of the surface defects’ density than by variation of excess surface charge induced by adsorbed oxygen species.