Analysis of SiOxCyHz polymeric materials by x-ray absorption spectroscopy: Anomalous behavior of the resonant SiKLL Auger spectra

Abstract

Silicone-like SiOxCyHz polymeric thin films with different C∕O atomic ratios have been studied by x-ray absorption spectroscopy and resonant Auger electron spectroscopy. The energy of the onset of the SiK absorption edge varies with the film composition from the value observed in SiC (i.e.,∼1840eV) to that in SiO2 (i.e.,∼1844eV). In the samples with a low C∕O atomic ratio (i.e.,∼1),the main band of the SiK spectra depicts two well defined peaks that can be associated with the Si-C and Si-O bonds present in the samples. Their relative intensity can be used to assess the concentration of these two bond types. Resonant SiKLL Auger spectra of the polymeric thin film have been measured using photon energies across the SiK absorption edge. A first Auger peak appearing at a high kinetic energy was recorded for photon energies around the onset of the absorption edge and the first peak/shoulder of the SiK spectrum associated with the Si-C bonds. This resonant SiKLL Auger signal depicts the typical behavior of a resonant Auger process, i.e., its intensity increases when increasing the photon energy, passes through a maximum and then decreases to disappear. In parallel with the evolution of this resonant spectrum, a “normal” SiKLL Auger spectrum with a lower kinetic energy appeared for photon energies around the middle of the absorption curve. This spectrum is the only one prevailing at photon energies well above the absorption edge. An outstanding behavior of the SiKLL resonant Auger peaks in the polymers with a high C∕O atomic ratio (i.e., ⩾4) is that they present a negative dispersion with photon energy, i.e., their kinetic energy decreases as the photon energy increases. This behavior is opposite to that generally found for resonant Auger peaks in most systems and particularly for SiO2. Although the origin of such behavior is still unclear, the study of the SiK absorption edge and the corresponding SiKLL resonant Auger spectra results helpful for the structural and electronic characterization of SiOxCyHz polymers.