A non-resonant inelastic x-ray scattering study on silicon oxides and clathrates

Abstract

Silicon is still a dominating element in terms of industrial applications and also fundamental research. Silicon oxides play a key role for insulator layers in integrated circuits and coatings for opto-electric devices. A microscopic understanding of the silicon-oxide structure is therefore highly demanded. New nanostructured silicon compounds showing particular physical behavior have been discovered during the last decade. So, endohedrally doped silicon clathrates are promising materials for thermo-electric applications and tailored band-gaps. The study of the interaction between the guest atoms and the host silicon network is crucial to understand changes in physical properties. Also in the view of fundamental research silicon clathrates show exciting structural and electronic phase-transitions under high pressure. Access to the structural and electronic information in bulk amorphous silicon monoxide and complex silicon compounds can be achieved by the study of absorption edges. Non-resonant inelastic x-ray scattering is a powerful tool to measure shallow absorption edges using hard x-rays. This allows the study of low energy transitions under conditions which do not permit electrons and soft x-rays. In the present work, an algorithm is presented for the proper experimental extraction of momentum-transfer dependent scattering spectra. A comparison with ab-initio calculations can contribute significantly to the understanding of the experimental spectra. Therefore, the applicability and the limits of theoretical approaches are elaborated in a study of the pure elements silicon, magnesium and sodium. Based on these methodical advances, the disproportionation of bulk amorphous silicon monoxide is analyzed and compared to the interface clusters mixture model for the SiO structure. Complex nano-structured barium doped silicon networks are examined by the survey of the barium giant dipole resonance. The first observation of different modulations of the resonance depending on the structure will be presented and future applications on high-pressure research will be highlighted.