R. Verbeni

A perfect crystal X-ray analyser with 1.5 meV energy resolution

Abstract A new spherical silicon crystal analyser, operated in backscattering geometry at the Si(11 11 11) reflection, allows to perform inelastic X-ray scattering experiments with a total energy resolution of 1.5 ± 0.2 meV full-width-half-maximum (FWHM) at 22 keV incident photon energy. This analyser was constructed by improving a procedure recently developed.

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. 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.

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). 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.

Improving the performance of high-resolution X-ray spectrometers with position-sensitive pixel detectors

A dispersion-compensation method to remove the cube-size effect from the resolution function of diced analyzer crystals using a position-sensitive two-dimensional pixel detector is presented. For demonstration, a resolution of 23 meV was achieved with a spectrometer based on a 1 m Rowland circle and a diced Si(555) analyzer crystal in a near-backscattering geometry, with a Bragg angle of 88.5 degrees . In this geometry the spectrometer equipped with a traditional position-insensitive detector provides a resolution of 190 meV. The dispersion-compensation method thus allows a substantial increase in the resolving power without any loss of signal intensity.

Resonant inelastic hard x-ray scattering with diced analyzer crystals and position-sensitive detectors

A novel design of a high-resolution spectrometer is proposed for emission spectroscopy and resonant inelastic hard x-ray scattering applications. The spectrometer is based on a Rowland circle geometry with a diced analyzer crystal and a position-sensitive detector. The individual flat crystallites of the diced analyzer introduce a well-defined linear position-energy relationship within the analyzer focus. This effect can be exploited to measure emission spectra with an unprecedented resolution. For demonstration, a spectrometer was constructed using a diced Si(553) analyzer working at the CuK edge with an intrinsic resolution of 60meV. With the proposed design, spectrometers operating at the K edges of 3d transition metals can have intrinsic resolutions below 100meV even with analyzer crystals not working in Bragg-backscattering conditions.

X-ray Monochromator with 2 × 108 Energy Resolution

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.

High-frequency longitudinal and transverse dynamics in water

High-resolution, inelastic x-ray scattering measurements of the dynamic structure factor S (Q,omega) of liquid water have been performed for wave vectors Q between 4 and 30 nm(-1) in distinctly different thermodynamic conditions ( T=263-420 K ; at, or close to, ambient pressure and at P=2 kbar ). In agreement with previous inelastic x-ray and neutron studies, the presence of two inelastic contributions (one dispersing with Q and the other almost nondispersive) is confirmed. The study of their temperature and Q dependence provides strong support for a dynamics of liquid water controlled by the structural relaxation process. A viscoelastic analysis of the Q -dispersing mode, associated with the longitudinal dynamics, reveals that the sound velocity undergoes a complete transition from the adiabatic sound velocity ( c(0) ) (viscous limit) to the infinite-frequency sound velocity ( c(infinity) ) (elastic limit). On decreasing Q , as the transition regime is approached from the elastic side, we observe a decrease of the intensity of the second, weakly dispersing feature, which completely disappears when the viscous regime is reached. These findings unambiguously identify the second excitation to be a signature of the transverse dynamics with a longitudinal symmetry component, which becomes visible in S (Q,omega) as soon as the purely viscous regime is left.

Experimental setup for high energy photoemission using synchrotron radiation

The instrument VOLPE (volume photoemission from solids) is an experimental setup dedicated to high energy photoemission (PE) experiments. The instrument is equipped with an electrostatic hemispherical spectrometer especially designed to analyze high energy electrons (up to 10 keV) with high resolving power. In order to attain an energy resolution of a few tens of millielectron volts, we designed and constructed a dedicated input lens system, high stability power supplies, and a low dark-count detector and readout electronics. The system has been tested and is now operational on the ID16 beamline at European Synchrotron Radiation Facility, where an optical layout has been developed to perform high energy, high resolution PE experiments. First results show an overall energy resolution (electron + photon) of 71+/-7 meV at 5934 eV. The effective attenuation length of the photoelectrons is estimated to be 5+/-0.5 nm at a kinetic energy of 5 keV

Microscopic relaxation in supercritical and liquid neon

The high frequency behavior of the dynamic structure factor, S(Q,ω), of liquid and supercritical neon is investigated by inelastic x-ray scattering at different temperatures and pressure. The spectral evolution is described in terms of a single-relaxation-time viscoelastic model. The occurrence of a positive dispersion in the sound velocity is clearly visible in both investigated thermodynamic phases. The anomalies in the dispersive behavior deeply reduce at the higher temperatures, probably, as a consequence of important changes in the first shell interactions. More generally, the atomic dynamics is dominated by a relaxation process whose time scale is in the range of fast microscopic degrees of freedom (≈10−13 s), and whose strength and typical time scale stay constant over all the explored liquid and supercritical regions.

Acoustic nature of the boson peak in vitreous silica

New temperature-dependent inelastic X-ray scattering (IXS) and Raman scattering (RS) data are compared with each other and with existing inelastic neutron scattering (INS) data in vitreous silica, in the 300± 1775K region. The IXS data show collective propagating excitations up to Q ˆ 3:5nm i 1 . The temperature behaviour of the excitations at Q ˆ 1:6nm i 1 matches that of the boson peak found in INS and RS. This supports the fact that the acoustic origin of the excess of vibrational states gives rise to the boson peak in this glass.