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Pressure is the cleanest way to tune heavy fermion systems to a quantum phase transition in order to study the rich physics and competing phases, and the comparison between ytterbium and cerium systems is particularly fruitful. We briefly review the mechanisms in play and show some examples of expected and unexpected behaviour. We emphasise the importance of the valence changes under pressure and show how modern synchrotron techniques can accurately determine this, including at low temperature. [ABSTRACT FROM AUTHOR]

In order to study the dynamic structure factor of hydrogen fluoride and its water solutions, we have realized a sample container able to resist these highly reacting hydrogen-bonded liquids and suitable for near-forward x-ray scattering experiments. The design and development of each part of the apparatus together with a discussion on the choice of the materials is reported. Two cells have been built for pure HF and for (HF)x(H2O)1-x solutions based on similar schemes but developed with different materials and some structural variations. Their contribution to the total scattered intensity has been measured. An example of inelastic x-ray scattering spectra at fixed temperature (T=283 K) and momentum transfer (Q=4 nm-1) is reported as a function of the concentration of hydrogen fluoride [(HF)x(H2O)1-x,with x=0,0.2,0.4,0.73,1]. [ABSTRACT FROM AUTHOR]

Abstract: High energy-resolution resonant inelastic X-ray scattering (RIXS) at the L2,3 edges of 3d transition metal compounds has proved to be a very powerful technique for the study of elementary excitations of various nature. In the case of cuprates, in particular, it was realized that magnetic excitations can be directly accessed, thus complementing neutron scattering experiments. It is clearly desirable to extend this technique to 5d transition metal compounds, whose L2,3 edges lie in the hard X-ray energy range. In the case of Ir, the L3 edge is found at 11.215keV. To access excitations energies similar to those of magnetic excitations in cuprates, a resolving power better than ≈105 is needed. Here, we describe the hard X-ray RIXS set-up at the ID16 beam line at the European Synchrotron Radiation Facility (ESRF), suitable for L3 edge RIXS studies of Ir oxides, with a combined energy-resolution of 36meV, i.e. a resolving power of 3×105. [Copyright &y& Elsevier]

We provide a complete picture of the valence instabilities of Yb in the heavy-fermion compound YbCu2Si2 by resonant inelastic x-ray scattering measurements (RIXS) at the Yb L3 edge under high pressure (up to 22 GPa) and at low temperatures (down to 7 K) in the vicinity of the magnetic ordered state. The valence shows a significant increase with pressure without reaching the full trivalent state even at the highest pressure. Its pressure dependence is marked by a pronounced change of slope around 10 GPa, a value close to the magnetic critical pressure Pc≈ 8 GPa. Our results suggest that magnetic order in YbCu2Si2 appears for a valence value v < 3. Unlike CeCu2Si2, valence fluctuations do not sustain superconductivity, which is likely destroyed by ferromagnetism. [ABSTRACT FROM AUTHOR]

The design and first results of a large-solid-angle X-ray emission spectrometer that is optimized for energies between 1.5 keV and 5.5 keV are presented. The spectrometer is based on an array of 11 cylindrically bent Johansson crystal analyzers arranged in a non-dispersive Rowland circle geometry. The smallest achievable energy bandwidth is smaller than the core hole lifetime broadening of the absorption edges in this energy range. Energy scanning is achieved using an innovative design, maintaining the Rowland circle conditions for all crystals with only four motor motions. The entire spectrometer is encased in a high-vacuum chamber that allocates a liquid helium cryostat and provides sufficient space for in situ cells and operando catalysis reactors.

Corrections to the paper by Honkanen et al. (2014). [J. Synchrotron Rad. 21, 104-110] are made.

We present the development, manufacturing, and performance of spherically bent crystal analyzers (SBCAs) of 100 mm diameter and 0.5 m bending radius. The elastic strain in the crystal wafer is partially released by a "strip-bent" method where the crystal wafer is cut into strips prior to the bending and the anodic bonding process. Compared to standard 1 m SBCAs, a gain in intensity is obtained without loss of energy resolution. The gain ranges between 2.5 and 4.5, depending on the experimental conditions and the width of the emission line measured. This reduces the acquisition times required to perform high energy-resolution x-ray absorption and emission spectroscopy on ultra-dilute species, accessing concentrations of the element of interest down to, or below, the ppm (ng/mg) level.

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. Notably, such a crossover is accompanied by a cusp-like behavior in the pressure dependence of the elastic response of the system. Overall, the presented results highlight the complex fingerprint of PA phenomena on the high-frequency phonon dispersion.

Hydration of sulfuric acid plays a key role in new-particle formation in the atmosphere. It has been recently proposed that proton dynamics is crucial in the stabilization of these clusters. One key question is how water molecules mediate proton transfer from sulfuric acid, and hence how the deprotonation state of the acid molecule behaves as a function concentration. We address the proton transfer in aqueous sulfuric acid with O K edge and S L edge core-excitation spectra recorded using inelastic X-ray scattering and with ab initio molecular dynamics simulations in the concentration range of 0-18.0 M. Throughout this range, we quantify the acid-water interaction with atomic resolution. Our simulations show that the number of donated hydrogen bonds per Owater increases from 1.9 to 2.5 when concentration increases from 0 to 18.0 M, in agreement with a rapid disappearance of the pre-edge feature in the O K edge spectrum. The simulations also suggest that for 1.5 M sulfuric acid SO4(2-) is most abundant and that its concentration falls monotonously with increasing concentration. Moreover, the fraction of HSO4(-) peaks at ∼12 M.

Wavelength-dispersive high-resolution X-ray spectrometers often employ elastically bent crystals for the wavelength analysis. In a preceding paper [Honkanen et al. (2014). J. Synchrotron Rad. 21, 104-110] a theory for quantifying the internal stress of a macroscopically large spherically curved analyser crystal was presented. Here the theory is applied to compensate for the corresponding decrease of the energy resolution. The technique is demonstrated with a Johann-type spectrometer using a spherically bent Si(660) analyser in near-backscattering geometry, where an improvement in the energy resolution from 1.0 eV down to 0.5 eV at 9.7 keV incident photon energy was observed.

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. We compare the experimental results to a charge-transfer cluster-model calculation, and a LSDA + U calculation of the ground state as a function of lattice constant. We thus show how resonant inelastic x-ray scattering spectroscopy is able to give insights into the manifold of excited states even in conditions that are difficult to access with many traditional experimental techniques.

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. The results from the calculation agree very well with experimental results obtained using an inelastic X-ray scattering synchrotron beamline.

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). X-ray spectroscopy, in principle, offers information on element composition and chemical environment. However, its application in 3D imaging over macroscopic length scales has not been possible for light elements. Here we introduce a new hard-X-ray spectroscopic tomography with a unique sensitivity to light elements. In this method, dark-field section images are obtained directly without any reconstruction algorithms. We apply the method to acquire the 3D structure and map the chemical bonding in selected samples relevant to materials science. The novel aspects make this technique a powerful new imaging tool, with an inherent access to the molecular-level chemical environment., (© 2011 Macmillan Publishers Limited. All rights reserved)

We measured the dynamic structure factor of the liquid and glassy phases of the LiCl-6H(2)O solution by means of inelastic scattering of radiation in the visible, UV, and x-ray range, between 1 GHz and 10 THz, and by means of photon-correlation spectroscopy, between 0.01 Hz and 20 kHz. The measurements were performed in the temperature range between 353 and 80 K. Our data show that a single-relaxation process exists at high temperature, which has features similar to those of the single relaxation of pure water. Upon cooling the system below approximately 220 K, this single mode starts to differentiate two processes, a structural (alpha-) and a secondary (beta-) relaxation. As the temperature is decreased, the beta-relaxation is the vanishing continuation of the single, high-temperature process, while the onset of the alpha-relaxation occurs at the expense of the beta-process.

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. The spectrometer is based on a Rowland circle design with fixed Bragg angles of about 88 degrees . The energy resolution can be chosen between 30-2000 meV with typical incident-photon energies of 6-13 keV. The spectrometer is optimized for studies of valence and core electron excitations resolving both energy and momentum transfer.

The energy scale of a triple-axis x-ray spectrometer with meV energy resolution based on perfect silicon crystal optics is calibrated, utilizing the most recent determination of the silicon lattice parameter and its thermal expansion coefficient and recording the dispersion of longitudinal acoustic and optical phonons in a diamond single crystal and the molecular vibration mode in liquid nitrogen. Comparison of the x-ray results with previous inelastic neutron and Raman scattering results as well as with ab initio phonon dispersion calculations yields an overall agreement better than 2%.

The high-frequency acoustic dynamics of sulfur across the liquid-liquid, lambda transition has been studied using inelastic x-ray scattering. The combination of these high-frequency data with lower frequency, literature data indicates that liquid sulfur develops, in the high-temperature, polymeric solution phase, some characteristic features of a rubber. In particular, entanglement coupling among polymeric chains plays a relevant role in the dynamics of this liquid phase.

The dynamic structure factor of m-toluidine has been measured by inelastic x-ray scattering in the mesoscopic Q range between 1 and 10 nm(-1), where a prepeak is revealed in the static structure factor resulting from the existence of hydrogen bonded, nanometer size clusters. Evidence is given of (i) a square-root cusp in the nonergodicity factor and of (ii) critical nonergodicity parameters which oscillate in phase with the static structure factor. These results demonstrate that local order in a liquid can coexist with the signatures of the ergodic to nonergodic transition predicted by the mode coupling theory for simple, dense liquids.

An X-ray beam of 3 x 10(7) photons s(-1) with 2 x 10(8) relative energy resolution has been obtained at a third-generation synchrotron undulator X-ray source using the (13 13 13) Bragg reflection from a silicon perfect crystal. The production of these 25.70 keV X-rays with 450 +/- 50 mueV bandpass opens up new possibilities in X-ray optics and spectroscopies.