The shape of the Ba 4d-4f giant dipole resonance is studied for Ba atoms embedded inside complex Si networks covering structures consisting of Si nanocages and nanotubes, i.e. the clathrate Ba8Si46, the complex compound BaSi6, and the semiconducting BaSi2. Here, non-resonant x-ray Raman scattering is used to investigate confinement effects on the shape of the giant resonance in the vicinity of the Ba N-IV, V-edge. The distinct momentum transfer dependence of the spectra is analyzed and discussed. The measurements are compared to calculations of the giant resonance within time-dependent local density approximation in the dipole limit. No modulation of the giant resonance's shape for Ba atoms confined in different local environments was observed, in contrast to the calculations. The absence of such shape modulation for complex Ba/Si compounds is discussed providing important implications for further studies of giant resonance phenomena utilizing both theory and experiment.

The microscopic structure of disproportionating amorphous silicon monoxide is studied by inelastic x-ray scattering at the silicon ${L}_{\text{II},\text{III}}$ edge. This material arranges into nanocrystalline regions of Si embedded in amorphous ${\text{SiO}}_{2}$ at proper annealing temperatures and in this work we demonstrate how the contribution of the suboxide interfaces between these regions can be extracted from the experimental data. The resulting near-edge spectra are analyzed in detail using a computational framework that combines molecular-dynamics simulations and density-functional theory calculations. The results indicate that the amount of silicon atoms with oxidation states between $+1$ and $+3$ is significant and depends strongly on the annealing temperature. Furthermore, the presented $s$, $p$, and $d$-type local densities of states $(\ensuremath{\ell}\text{DOS})$ demonstrate that the most significant differences are found in the $p$-type $\ensuremath{\ell}\text{DOS}$.

We present an x-ray scattering study of the temperature-induced phase separation and Si nanocrystal formation in bulk amorphous SiOx with x≈1. X-ray Raman scattering at the Si LII,III-edge reveals a significant contribution of suboxides present in native amorphous SiO. The suboxide contribution decreases with increasing annealing temperature between 800–1200 °C pointing toward a phase separation of SiO into Si and SiO2 domains. In combination with x-ray diffraction and small angle x-ray scattering the SiO microstructure is found to be dominated by internal suboxide interfaces in the native state. For higher annealing temperatures above 900 °C growth of Si nanocrystals with rough surfaces embedded in a silicon oxide matrix can be observed.

The temperature-induced phase separation of native amorphous germanium monoxide, a-GeO, into Ge and GeO2 was studied by measurements of the Ge K-edge employing partial fluorescence yield detection. In the native a-GeO samples a significant amount of sub-oxides was found. This sub-oxide content decreases with increasing annealing temperature. At elevated temperatures the formation of nanocrystals was observed. The results indicate a structure of a-GeO which consists of nanoscaled Ge and GeO2 clusters separated by sub-oxide interfaces.

Non-resonant inelastic X-ray scattering of core electrons is a prominent tool for studying site-selective, i.e. momentum-transfer-dependent, shallow absorption edges of liquids and samples under extreme conditions. A bottleneck of the analysis of such spectra is the appropriate subtraction of the underlying background owing to valence and core electron excitations. This background exhibits a strong momentum-transfer dependence ranging from plasmon and particle-hole pair excitations to Compton scattering of core and valence electrons. In this work an algorithm to extract the absorption edges of interest from the superimposed background for a wide range of momentum transfers is presented and discussed for two examples, silicon and the compound silicondioxide.

Double plasmons are unique fingerprints of dynamical correlations in the model of a free-electron gas beyond the random phase approximation. A combined experimental and theoretical study of double-plasmon excitations in three simple metals Na, Mg, and Al is presented. The intensities, spectral shapes, and dispersions of these excitations are analyzed as a function of momentum. The measured double-plasmon intensity is found to increase with a decreasing electron density, which is in good agreement with the expectations of strength of the correlation effects as a function of the electron gas density. The overall quantitative agreement between the experimental and the theoretical results is very good, while the remaining discrepancies may be due to higher order correlation effects and band-structure effects.

The giant dipole resonance of Ba embedded into the complex Si host lattice structure of Ba8Si46 has been observed under ambient and high-pressure conditions. The measurements have been accomplished using nonresonant inelastic x-ray scattering for different momentum transfers. The resonance appears as a broad feature between 100- and 150-eV energy loss for low momentum transfer but vanishes for high momentum transfer. Calculations within the time-dependent local-density approximation have been performed by means of a real-space multiple-scattering Green's-function approach. The results reproduce the shape and the width of the observed resonance. Modulations of the giant resonance spectra are predicted by computations ranging from ambient pressure up to 20 GPa which can be used to study the local environment of the Ba guest. A corresponding experimental setup for high-pressure studies is presented, potential applications to study the phase transitions of Ba clathrates are discussed, and first experimental results are shown.

Calculations of the nonresonant inelastic x-ray spectra for L edges of Si, Mg, and Na have been performed using a Bethe-Salpeter equation approach and an implementation of a real-space multiple-scattering Green's function approach. The computational results are compared with each other and with the measured spectra. It is shown to what extent both methods reproduce the general shape of the edges, their fine structure, and the dependence on the momentum transfer and thus on the weight of dipole and multipole transitions. Characteristics of the calculations concerning screening and the calculation of the density of states are also discussed in detail. The comparison between the multiple-scattering approach, the more sophisticated calculations using the Bethe-Salpeter approach, and experiment on these simple systems is essential for applications of real-space multiple-scattering calculations on more complex systems, which are not accessible by other computational methods.

X-ray photon-correlation spectroscopy is used to measure the dynamic structure factor f(q,tau) of gold particles moving on the surface of thin polymer films. Above the glass transition of the polymer the peculiar form f(q,tau) approximately exp[-(Gamma tau)(alpha)] is found with 0.7 < alpha < 1.5, depending on sample age and temperature. The relaxation rates Gamma scale linearly with q, excluding a simple Brownian diffusive motion. This type of behavior, already observed in aging bulk soft matter systems, is explained by a power law distribution of particle velocities due to ballistic motion.