Signature of a polyamorphic transition in the THz spectrum of vitreous GeO2.

The THz spectrum of density fluctuations, S(Q, ω), of vitreous GeO2 at ambient temperature was measured by inelastic x-ray scattering from ambient pressure up to pressures well beyond that of the known α-quartz to rutile polyamorphic (PA) transition. We observe significant differences in the spectral shape measured below and above the PA transition, in particular, in the 30-80 meV range. Guided by first-principle lattice dynamics calculations, we interpret the changes in the phonon dispersion as the evolution from a quartz-like to a rutile-like coordination.

Shear propagation in the terahertz dynamics of water-glycerol mixtures.

Inelastic X-ray and neutron scattering techniques were jointly used to investigate the dynamics of water-glycerol mixtures at different concentrations and temperatures. It was observed that even relatively low concentrations of glycerol increase the damping of shear modes, as a consequence of the known ability of glycerol to disrupt the hydrogen bond network of water. A similar trend was observed when increasing the temperature, which suggests the presence of a locus in the concentration-temperature plane marking a crossover in the shear modulus.

Tracing X-rays through an L-shaped laterally graded multilayer mirror: a synchrotron application.

A theoretical model to trace X-rays through an L-shaped (nested or Montel Kirkpatrick-Baez mirrors) laterally graded multilayer mirror to be used in a synchrotron application is presented. The model includes source parameters (size and divergence), mirror figure (parabolic and elliptic), multilayer parameters (reflectivity, which depends on layer material, thickness and number of layers) and figure errors (slope error, roughness, layer thickness fluctuation Deltad/d and imperfection in the corners). The model was implemented through MATLAB/OCTAVE scripts, and was employed to study the performance of a multilayer mirror designed for the analyzer system of an ultrahigh-resolution inelastic X-ray scattering spectrometer at National Synchrotron Light Source II.