Uniqueness of glasses prepared via x-ray induced yielding.

The yield point marks the beginning of plastic deformation for a solid subjected to sufficient stress, but it can alternatively be reached by x-ray irradiation. We characterize this latter route in terms of thermodynamics, structure and dynamics for a series of GeSechalcogenide glasses with different amount of disorder. We show that a sufficiently long irradiation at room temperature results in a stationary and unique yielding state, independent of the initial state of the glass.

A new experimental setup for combined fast differential scanning calorimetry and X-ray photon correlation spectroscopy.

Synchrotron-radiation-based techniques are a powerful tool for the investigation of materials. In particular, the availability of highly brilliant sources has opened the possibility to develop techniques sensitive to dynamics at the atomic scale such as X-ray photon correlation spectroscopy (XPCS). XPCS is particularly relevant in the study of glasses, which have been often investigated at the macroscopic scale by, for example, differential scanning calorimetry.

Stochastic atomic acceleration during the X-ray-induced fluidization of a silica glass.

The X-ray-induced, nonthermal fluidization of the prototypical SiO glass is investigated by X-ray photon correlation spectroscopy in the small-angle scattering range. This process is initiated by the absorption of X-rays and leads to overall atomic displacements which reach at least few nanometers at temperatures well below the glass transition. At absorbed doses of ∼5 GGy typical of many modern X-ray-based experiments, the atomic displacements display a hyperdiffusive behavior and are distributed according to a heavy-tailed, Lévy stable distribution.

Structural changes across thermodynamic maxima in supercooled liquid tellurium: A water-like scenario.

Liquid polymorphism is an intriguing phenomenon that has been found in a few single-component systems, the most famous being water. By supercooling liquid Te to more than 130 K below its melting point and performing simultaneous small-angle and wide-angle X-ray scattering measurements, we observe clear maxima in its thermodynamic response functions around 615 K, suggesting the possible existence of liquid polymorphism. A close look at the underlying structural evolution shows the development of intermediate-range order upon cooling, most strongly around the thermodynamic maxima, which we attribute to bond-orientational ordering.

Universal Two-Component Dynamics in Supercritical Fluids.

Despite the technological importance of supercritical fluids, controversy remains about the details of their microscopic dynamics. In this work, we study four supercritical fluid systems─water, Si, Te, and Lennard-Jones fluid─via classical molecular dynamics simulations. A universal two-component behavior is observed in the intermolecular dynamics of these systems, and the changing ratio between the two components leads to a crossover from liquidlike to gaslike dynamics, most rapidly around the Widom line.

Two-Component Dynamics and the Liquidlike to Gaslike Crossover in Supercritical Water.

Molecular-scale dynamics in sub- to supercritical water is studied with inelastic x-ray scattering and molecular dynamics simulations. The obtained longitudinal current correlation spectra can be decomposed into two main components: a low-frequency (LF), gaslike component and a high-frequency (HF) component arising from the O-O stretching mode between hydrogen-bonded molecules, reminiscent of the longitudinal acoustic mode in ambient water. With increasing temperature, the hydrogen-bond network diminishes and the spectral weight shifts from HF to LF, leading to a transition from liquid- to gaslike dynamics with rapid changes around the Widom line.

Lithium Borates from the Glass to the Melt: A Temperature-Induced Structural Transformation Viewed from the Boron and Oxygen Atoms.

A multiedge study of the local structure of lithium borate glasses and melts has been carried out using X-ray Raman scattering (XRS) as a function of temperature. Thanks to a wide range of compositions, from pure BO up to the metaborate composition, we are able to finely interpret the modifications of the local environment of both the boron and oxygen atoms in terms of boron coordination number, formation of nonbridging oxygens (NBOs), and polymerization degree of the borate framework as a function of temperature and composition. A temperature-induced B to B conversion is observed above the glass transition temperature () from the glass to the melt from the triborate composition up to the metaborate composition.

Resonant inelastic X-ray scattering of magnetic excitations under pressure.

Resonant inelastic X-ray scattering (RIXS) is an extremely valuable tool for the study of elementary, including magnetic, excitations in matter. The latest developments of this technique have mostly been aimed at improving the energy resolution and performing polarization analysis of the scattered radiation, with a great impact on the interpretation and applicability of RIXS. Instead, this article focuses on the sample environment and presents a setup for high-pressure low-temperature RIXS measurements of low-energy excitations.

Damping of vibrational excitations in glasses at terahertz frequency: The case of 3-methylpentane.

We report a compared analysis of inelastic X ray scattering (IXS) and of low frequency Raman data of glassy 3-methylpentane. The IXS spectra have been analysed allowing for the existence of two distinct excitations at each scattering wavevector obtaining a consistent interpretation of the spectra. In particular, this procedure allows us to interpret the linewidth of the modes in terms of a simple model which relates them to the width of the first sharp diffraction peak in the static structure factor.

Study on the reflectivity properties of spherically bent analyser crystals. Corrigendum.

Corrections to the paper by Honkanen et al. (2014). [J.

Resonant X-ray emission with a standing wave excitation.

The Borrmann effect is the anomalous transmission of x-rays in perfect crystals under diffraction conditions. It arises from the interference of the incident and diffracted waves, which creates a standing wave with nodes at strongly absorbing atoms. Dipolar absorption of x-rays is thus diminished, which makes the crystal nearly transparent for certain x-ray wave vectors.

Improving the energy resolution of bent crystal X-ray spectrometers with position-sensitive detectors.

Wavelength-dispersive high-resolution X-ray spectrometers often employ elastically bent crystals for the wavelength analysis. In a preceding paper [Honkanen et al. (2014).

Interplay between temperature-activated vibrations and nondipolar effects in the valence excitations of the CO₂ molecule.

We report a study on the temperature dependence of the valence electron excitation spectrum of CO2 performed using nonresonant inelastic X-ray scattering spectroscopy. The excitation spectra were measured at the temperatures of 300 and 850 K with momentum-transfer values of 0.4-4.

Crystal-field excitations in NiO under high pressure studied by resonant inelastic x-ray scattering.

We report a study on charge-neutral crystal-field (dd) excitations in NiO as a function of applied pressure up to 55 GPa, using resonant inelastic x-ray scattering spectroscopy at the Ni K edge. We find distinct signatures of the pressure-induced modifications to the 3d orbital energies as a function of pressure. These modifications are experimentally evidenced by a subtle splitting of the dd-excitation resonance energies.

Study on the reflectivity properties of spherically bent analyser crystals.

Theoretical and experimental studies are presented on properties of spherically bent analyser crystals for high-resolution X-ray spectrometry. A correction to the bent-crystal strain field owing to its finite surface area is derived. The results are used to explain the reflectivity curves and anisotropic properties of Si(660) and Si(553) analysers in near-backscattering geometry.

Saturation behavior in X-ray Raman scattering spectra of aqueous LiCl.

We report a study on the hydrogen-bond network of water in aqueous LiCl solutions using X-ray Raman scattering (XRS) spectroscopy. A wide concentration range of 0-17 mol/kg was covered. We find that the XRS spectral features change systematically at low concentrations and saturate at 11 mol/kg.

Thermal deformation of cryogenically cooled silicon crystals under intense X-ray beams: measurement and finite-element predictions of the surface shape.

X-ray crystal monochromators exposed to white-beam X-rays in third-generation synchrotron light sources are subject to thermal deformations that must be minimized using an adequate cooling system. A new approach was used to measure the crystal shape profile and slope of several cryogenically cooled (liquid nitrogen) silicon monochromators as a function of beam power in situ and under heat load. The method utilizes multiple angular scans across the Bragg peak (rocking curve) at various vertical positions of a narrow-gap slit downstream from the monochromator.

X-ray-Raman-scattering-based EXAFS beyond the dipole limit.

X-ray Raman scattering (XRS) provides a bulk-sensitive method of measuring the extended X-ray absorption fine structure (EXAFS) of soft X-ray absorption edges. Accurate measurements and data analysis procedures for the determination of XRS-EXAFS of polycrystalline diamond are described. The contributions of various angular-momentum components beyond the dipole limit to the atomic background and the EXAFS oscillations are incorporated using self-consistent real-space multiple-scattering calculations.

Temperature dependence of the near-edge spectrum of water.

The interpretation of the oxygen near-edge spectrum of water has been debated intensively. We present new measurements of the temperature dependence of the spectrum and perform a van't Hoff analysis for the pre-edge intensity. Many microscopical and thermodynamic properties of liquid water have been described in the literature in terms of mixture models, which presume the existence of two distinct species with different local structures.

Direct tomography with chemical-bond contrast.

Three-dimensional (3D) X-ray imaging methods have advanced tremendously during recent years. Traditional tomography uses absorption as the contrast mechanism, but for many purposes its sensitivity is limited. The introduction of diffraction, small-angle scattering, refraction, and phase contrasts has increased the sensitivity, especially in materials composed of light elements (for example, carbon and oxygen).

Role of non-hydrogen-bonded molecules in the oxygen K-edge spectrum of ice.

We report the oxygen K-edge spectra of ices Ih, VI, VII, and VIII measured with X-ray Raman scattering. The pre-edge and main-edge contributions increase strongly with density, even though the hydrogen bond arrangements are very similar in these phases. While the near-edge spectral features in water and ice have often been linked to hydrogen bonding, we show that the spectral changes in the phases studied here can be quantitatively related to structural changes in the second coordination shell.

Phonon spectroscopy at high pressure by inelastic X-ray scattering.

The current status of phonon-dispersion studies at high pressure using very high energy resolution inelastic X-ray scattering is discussed. A brief description of the instrumental apparatus is given, together with an illustration of the high-pressure facilities available at the IXS beamlines ID16 and ID28 of the ESRF. Some selected examples of recent studies on crystalline and liquid samples in a diamond anvil cell are then presented.

Anomalous properties of the acoustic excitations in glasses on the mesoscopic length scale.

The low-temperature thermal properties of dielectric crystals are governed by acoustic excitations with large wavelengths that are well described by plane waves. This is the Debye model, which rests on the assumption that the medium is an elastic continuum, holds true for acoustic wavelengths large on the microscopic scale fixed by the interatomic spacing, and gradually breaks down on approaching it. Glasses are characterized as well by universal low-temperature thermal properties that are, however, anomalous with respect to those of the corresponding crystalline phases.

High frequency dynamics in liquid Cs at high pressure.

We report on an inelastic x-ray scattering investigation of the high frequency dynamics of liquid cesium at 493 K and 1 GPa, which corresponds to a density 23% higher than that at the room pressure melting point. The analysis of the spectra, performed within the framework of the memory function approach suggests the existence of two different relaxation processes, i.e.

Multiple-element spectrometer for non-resonant inelastic X-ray spectroscopy of electronic excitations.

A multiple-analyser-crystal spectrometer for non-resonant inelastic X-ray scattering spectroscopy installed at beamline ID16 of the European Synchrotron Radiation Facility is presented. Nine analyser crystals with bending radii R = 1 m measure spectra for five different momentum transfer values simultaneously. Using a two-dimensional detector, the spectra given by all analysers can be treated individually.