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

A. Barranco, A. Yanguas-Gil, F. Yubero, A.R. González-Elipe
Journal of Applied Physics, 100 (2006) 033706 (1-7)
doi: 10.1063/1.2222043

Silicone-like ${SiO}_{x} C_{y} H_{z}$ 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 $Si K$ absorption edge varies with the film composition from the value observed in $SiC$ (i.e., $\sim 1840 eV$ ) to that in ${SiO}_{2}$ (i.e., $\sim 1844 eV$ ). In the samples with a low $C ∕ O$ atomic ratio (i.e., $\sim 1$ ),the main band of the $Si K$ 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 $Si K L L$ Auger spectra of the polymeric thin film have been measured using photon energies across the $Si K$ 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 $Si K$ spectrum associated with the $Si - C$ bonds. This resonant $Si K L L$ 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” $Si K L L$ 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 $Si K L L$ 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 ${SiO}_{2}$ . Although the origin of such behavior is still unclear, the study of the $Si K$ absorption edge and the corresponding $Si K L L$ resonant Auger spectra results helpful for the structural and electronic characterization of ${SiO}_{x} C_{y} H_{z}$ polymers.

Etiquetado en:2006 A. Barranco A. Yanguas-Gil A.R. González-Elipe Francisco Yubero Journal of Applied Physics