The Extremely Brilliant Source (EBS), the first high-energy 4th-generation synchrotron radiation source, constructed at the ESRF and based upon the novel concept of a Hybrid Multi-Bend Achromat (HMBA), has started user operation on August 25th, 2020. We report here on selected recent scientific results exploiting the greatly improved performances of this novel X-ray source.

The Extremely Brilliant Source (EBS) is the experimental implementation of the novel Hybrid Multi Bend Achromat (HMBA) storage ring magnetic lattice concept, which has been realised at European Synchrotron Radiation Facility. We present its successful commissioning and first operation. We highlight the strengths of the HMBA design and compare them to the previous designs, on which most operational synchrotron X-ray sources are based. We report on the EBS storage ring’s significantly improved horizontal electron beam emittance and other key beam parameters. EBS extends the reach of synchrotron X-ray science confirming the HMBA concept for future facility upgrades and new constructions.

The chemical and physical alterations of cadmium yellow (CdS) paints in Henri Matisse’s The Joy of Life (1905–1906, The Barnes Foundation) have been recognized since 2006, when a survey by portable X-ray fluorescence identified this pigment in all altered regions of the monumental painting. This alteration is visible as fading, discoloration, chalking, flaking, and spalling of several regions of light to medium yellow paint. Since that time, synchrotron radiation-based techniques including elemental and spectroscopic imaging, as well as X-ray scattering have been employed to locate and identify the alteration products observed in this and related works by Henri Matisse. This information is necessary to formulate one or multiple mechanisms for degradation of Matisse’s paints from this period, and thus ensure proper environmental conditions for the storage and the display of his works. This paper focuses on 2D full-field X-ray Near Edge Structure imaging, 2D micro-X-ray Diffraction, X-ray Fluorescence, and Fourier Transform Infra-red imaging of the altered paint layers to address one of the long-standing questions about cadmium yellow alteration—the roles of cadmium carbonates and cadmium sulphates found in the altered paint layers. These compounds have often been assumed to be photo-oxidation products, but could also be residual starting reagents from an indirect wet process synthesis of CdS. The data presented here allow identifying and mapping the location of cadmium carbonates, cadmium chlorides, cadmium oxalates, cadmium sulphates, and cadmium sulphides in thin sections of altered cadmium yellow paints from The Joy of Life and Matisse’s Flower Piece (1906, The Barnes Foundation). Distribution of various cadmium compounds confirms that cadmium carbonates and sulphates are photo-degradation products in The Joy of Life, whereas in Flower Piece, cadmium carbonates appear to have been a [(partially) unreacted] starting reagent for the yellow paint, a role previously suggested in other altered yellow paints.

Que ce soit en France, en Europe, aux États-Unis, au Japon ou ailleurs dans le monde, trois mots-clés reviennent toujours lorsqu’on présente les synchrotrons et leurs activités : pluridisciplinarité, brillance, utilisateurs. Ces très grands instruments de la physique, considérés comme les sources de lumière les plus sophistiquées et les plus performantes, sont, en effet, au service de dizaines de milliers de chercheurs dans le monde, irriguant toutes les disciplines scientifiques. C’est ce qui constitue leur atout principal en tant qu’infrastructures de recherche : favoriser les synergies entre disciplines et les collaborations entre équipes en proposant, au même endroit et au même moment, un panel de techniques expérimentales et de compétences.

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We discuss Extended X-ray Absorption Fine Structure (EXAFS) experiments on impurities in semiconductors. The local structure of the impurity site is determined for the first, second and third neighbor shells. These studies are carried out on absorption edges in the soft x-ray region using a novel fluorescence detection scheme which reveals improved detection sensitivity when compared with more standard electron Auger yield methods. The higher detection sensitivity allows structural studies at atomic densities as low as 1018 at/cm3 and this technique is used to study the local structure of P and S impurities in GaAs and of S in AlxGa1-xAs at concentrations of 1019–1020 at/cm3. The P atoms are substitutional on As sites, and a breathing relaxation of the P first shell Ga atoms is responsible for a P-Ga distance of 2.38A, which is 0.07A shorter than the As-Ga distance in GaAs(2.45A). No detectable relaxation is observed in the P second and third atomic shells. In Sdoped GaAs we find two different populations of S-Ga bonds with nearly equal intensity and both with S located on the As sub-lattice. These findings indicate two different configurations of substitutional S in GaAs. The coexistence of two similarly populated, charge compensating configurations is the first structural evidence which allows us to explain the observation that in n-doped GaAs the electrical activity of donors is lower than the atomic concentration. Finally, we present experimental results on S impurities in AlxGa1-xAs (0.2<x<0.5). In this system, at the Al concentrations we studied, the S impurities are bound only to Al and not to Ga atoms. We report the formation of an extended complex which is discussed in connection with the structural identification of DX centers in these materials.

The pressure evolution of the sound velocity in liquid water in the terahertz regime, c(infinity), between 0.05 and 0.88 GPa, at room temperature, has been investigated by synchrotron inelastic x-ray scattering in a diamond anvil cell. We confirm previous results showing that c(infinity) increases with density much less than the adiabatic sound velocity c(s), which is reasonably related to the known structural modifications in the hydrogen bond network. At variance with a previous study where an anomaly was found in the density evolution of c(infinity)-most likely due to the nonisothermal character of the study-the present work reveals a smooth behavior of c(infinity), which could provide a useful constraint to the current theories on liquid water.

The microscopic dynamics of four prototype systems (water, ammonia, nitrogen, and neon) across the critical temperature has been investigated by means of high-resolution inelastic x-ray scattering. The experimental line shape has been described using a model based on the memory function formalism. Two main relaxations, the thermal and the structural one, were observed in all the investigated systems. We found that the microscopic mechanism driving the structural relaxation clearly changes, being mainly governed by intermolecular bond rearrangements below the critical temperature and by binary collisions above it. Moreover, we observed that the relative weight of the thermal relaxation systematically increases on approaching the critical temperature, thus allowing for the observation of a transition from an adiabatic to an isothermal regime of sound propagation. Finally, we found the presence of an additional instantaneous relaxation, likely related to the coupling between collective vibrational modes and intramolecular degrees of freedom.

The dynamic structure factor of vitreous silica is measured at terahertz frequencies by inelastic scattering of x rays (IXS) and neutrons (INS). The IXS experiment is performed at exchanged wave vectors q between 4 and 15 nm(-1) and at temperatures above and below the glass transition. The neutron time-of-flight technique is used as a high-resolution probe in a comparable q region. The data analysis confirms the presence of two inelastic features in the IXS spectra in the entire explored wave-vector range. The lower-frequency component is nondispersive and is observed by both IXS and INS around the boson peak frequency. The higher-frequency one, associated with the longitudinal-acoustic-like branch, is marked by a positive dispersion, confirming the results of a previous study [Ruzicka , Phys. Rev. B 69, 100201 (2004)]. As q increases, the vibrational modes of the disordered structure progressively lose their plane-wave character; for q around that of the first sharp diffraction peak, the dynamic structure factor converges to an effective density of vibrational states. The contribution of the terahertz vibrations to the thermal conductivity of vitreous silica is then evaluated by means of a Kubo-type formula for the diffusivity in disordered systems. The acousticlike modes that persist at terahertz frequencies represent a heat conduction channel which accounts for only a fraction, although relevant, of the thermal conductivity. The failure of this approach to fully describe the conductivity data is attributed to the nondiagonal elements of the heat current operator that are not experimentally accessible.

We study the nonlinear refraction of X-rays in highly ionized condensed matter by using a classical model of a cold electron plasma in a lattice of still ions coupled with Maxwell equations. We discuss the existence and stability of nonlinear waves. As a real-world example, we consider beam self-defocusing in crystalline materials (B, C, Li, Na). We predict that nonlinear processes become comparable to the linear ones for focused beams with powers of the order of mc(3)/ro (approximately 10 GW), the classical electron power. As a consequence, nonlinear phenomena are expected in currently exploited X-ray Free-Electron Lasers and in their future developments.

We study the nonlinear refraction of x rays in highly ionized condensed matter by using a classical model of a cold electron plasma in a lattice of still ions coupled with Maxwell equations. By employing a group-theoretical technique, we reduce the governing equations of the system to an integrable set of nonlinear ordinary differential equations, discussing the existence and stability of nonlinear waves. This allows us to define the effective Kerr coefficient n(2) at x rays. With reference to real-world crystalline materials (B, C, Li, and Na), we consider beam self-defocusing and predict that nonlinear processes become comparable to the linear ones for focused beams with powers on the order of mc(3)/r(0) (approximate to 10 GW), the classical electron power. As a consequence, nonlinear phenomena are expected to largely affect imaging experiments in currently exploited x-ray free-electron lasers and in their future developments.

A combined inelastic X-ray and neutron scattering experiment is performed on the prototypical glass vitreous silica. The complementarity of the two techniques is exploited to determine the dynamic structure factor in a wide range of energies and wavevectors. The vibrational-mode spectral density is then used to compute the high-temperature thermal conductivity. The acoustic-like modes persisting at THz frequencies are shown to represent a relevant heat conduction channel, although they cannot account for the entire thermal conductivity.

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%.

This paper aims to discuss the present understanding of the high frequency dynamics in liquid water, with particular attention to a specific phenomenon - the so-called fast sound - since its first appearance in the literature up to its most recent explanation. A particular role in this history is played by the inelastic x-ray scattering (IXS) technique, which - with its introduction in the middle '90- allowed to face a large class of problems related to the high frequency dynamics in disordered materials, such as glass and liquids. The results concerning the fast sound in water obtained using the IXS technique are here compared with the inelastic neutron scattering (INS) and molecular dynamics simulation works. The IXS work has allowed us to demonstrate experimentally the existence of two branches of collective modes in liquid water: one linearly dispersing with the momentum (apparent sound velocity of approximate to 3200 m/s, the "fast sound") and the other at almost constant energy (5 - 7 meV). It has been possible to show that the dispersing branch originates from the viscoelastic bend up of the ordinary sound branch. The study of this sound velocity dispersion, marking a transition from the ordinary sound, c. to the "fast sound", c, as a function of temperature, has made it possible to relate the origin of this phenomenon to a structural relaxation process, which presents many analogies to those observed in glass-forming systems. The possibility to estimate from the IXS data the value of the relaxation time, tau, as a function of temperature leads to relating the relaxation process to the structural re-arrangements induced by the making and breaking of hydrogen bonds. In this framework, it is then possible to recognize an hydrodynamical "normal" regime, i. e. when one considers density fluctuations whose period of oscillation is on a timescale long with respect to tau, and a solid-like regime in the opposite limit. In the latter regime, the density fluctuations feel the liquid as frozen and the sound velocity is much higher: this is 'last sound" whose value is equivalent to the sound velocity found in crystalline ice.

We have performed bulk and surface-sensitive inelastic x-ray scattering experiments on liquid indium with 3 meV energy resolution. The experimental data are well reproduced within a generalized hydrodynamic model including structural and microscopic relaxation processes. We find a longitudinal viscosity of 22 mPa s in the near-surface region compared to 7.4 mPa s in the bulk. The origin of the increase is associated with a slowing down of the collective dynamics in a subsurface region of 4.6 nm.