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Many-body localization (MBL) has attracted significant attention because of its immunity to thermalization, role in logarithmic entanglement entropy growth, and opportunities to reach exotic quantum orders. However, experimental realization of MBL in solid-state systems has remained challenging. Here, we report evidence of a possible phonon MBL phase in disordered GaAs/AlAs superlattices. Through grazing-incidence inelastic X-ray scattering, we observe a strong deviation of the phonon population from equilibrium in samples doped with ErAs nanodots at low temperature, signaling a departure from thermalization. This behavior occurs within finite phonon energy and wavevector windows, suggesting a localization-thermalization crossover. We support our observation by proposing a theoretical model for the effective phonon Hamiltonian in disordered superlattices, and showing that it can be mapped exactly to a disordered 1D Bose-Hubbard model with a known MBL phase. Our work provides momentum-resolved experimental evidence of phonon localization, extending the scope of MBL to disordered solid-state systems.

X-ray beams at energies tuned slightly below that of exact backscattering (extreme conditions, where X-ray back-diffraction is almost extinguished – called residual XBD) are better focused if the experiment is carried out at lower energies in order to avoid multiple-beam diffraction effects. Following previous work by the authors [Hönnicke, Conley, Cusatis, Kakuno, Zhou, Bouet, Marques & Vicentin (2014). J. Appl. Cryst. 47, 1658–1665], herein efforts are directed towards characterizing the residual XBD beam of an ultra-thin Si 220 crystal (UTSiXTAL) at ∼3.2 keV. To achieve the residual XBD condition the UTSiXTAL was cooled from 310 to 273 K. The results indicate that under this extreme condition the energy resolution can be further improved. Issues with the energy resolution measurements due to incoming beam divergence and the ultra-thin crystal flatness are discussed.

We used Inelastic X-ray Scattering to gain insight into the complex Terahertz dynamics of a diluted Au-nanoparticles suspension in glycerol. We observe that, albeit sparse, Au-nanoparticles leave clear signatures on the dynamic response of the system, the main one being an additional mode propagating at the nanoparticle-glycerol interface. A Bayesian inferential analysis of the lineshape reveals that such a mode, at variance with conventional acoustic modes, keeps a hydrodynamic-like behavior well beyond the continuous limit and down to sub-nanometer distances.

In biological membranes, lipid rafts are now thought to be transient and nanoscopic. However, the mechanism responsible for these nanoscopic assemblies remains poorly understood, even in the case of model membranes. As a result, it has proven extremely challenging to probe the physicochemical properties of lipid rafts at the molecular level. Here, we use all-atom molecular dynamics (MD) simulations and inelastic X-ray scattering (IXS), an intrinsically nanoscale technique, to directly probe the energy transfer and collective short-wavelength dynamics (phonons) of biologically relevant model membranes. We show that the nanoscale propagation of stress in lipid rafts takes place in the form of collective motions made up of longitudinal (compression waves) and transverse (shear waves) molecular vibrations. Importantly, we provide a molecular picture for the so-called van der Waals mediated "force from lipid" [Anishkin, A. et al. Proc. Natl. Acad. Sci. U.S.A. 2014, 111, 7898], a key parameter for the ionic channel mechano-transduction and the mechanism for the lipid transfer of molecular level stress [Aponte-Santamaria, C. et al. J. Am. Chem. Soc. 2017, 139, 13588]. Specifically, we describe how lipid rafts are formed and maintained through the propagation of molecular stress, lipid raft rattling dynamics, and a relaxation process. Eventually, the rafts dissipate through the self-diffusion of lipids making up the rafts. We also show that the molecular stress and viscoelastic properties of transient lipid rafts can be modulated through the use of hydrophobic biomolecules such as melatonin and tryptophan. Ultimately, the herein proposed mechanism describing the molecular interactions for the formation and dissolution of lipid rafts may offer insights as to how lipid rafts enable biological function.

International audience; We used the high-resolution Inelastic X-ray Scattering beamline of the Advanced Photon Source at Argonne National Laboratory to measure the terahertz spectrum of pure water and a dilute aqueous suspension of 15 nm diameter spherical Au nanoparticles (Au-NPs). We observe that, despite their sparse volume concentration of about 0.5%, the immersed NPs strongly influence the collective molecular dynamics of the hosting liquid. We investigate this effect through a Bayesian inference analysis of the spectral lineshape, which elucidates how terahertz transport properties of water change upon Au-NP immersion. In particular, we observe a nearly complete disappearance of the longitudinal acoustic mode and a mildly decreased ability to support shear wave propagation.

We consider here the possibility of shaping the high-frequency acoustic propagation in a liquid upon directional confinement. This hypothesis is investigated by Inelastic X-ray Scattering measurements on water confined in aligned multi-walled carbon nanotubes, in which the momentum transfer was either parallel or orthogonal to the confinement axis. The comparison between the spectra measured in these two scattering geometries highlights the anisotropic nature of the dynamic response of directionally confined water, thus potentially inspiring new pathways to shape high-frequency sound propagation in isotropic systems. Finally, a Bayesian analysis of measured spectra unravels close similarities in the phonon dispersions of multiwalled nanotubes and graphite.

Significance Although it is believed that the raft formation in a cell membrane is governed by a selective interaction of different lipids and proteins, mechanisms driving and regulating the lateral membrane heterogeneity remain poorly understood. Here, using multicomponent lipid mixtures and inelastic X-ray scattering, we provide a spatial–temporal window to study lipid–lipid interactions. We show experimental evidence for the formation of dynamic lipid pairs, which are subnanometer in size and have a subnanosecond lifetime. These pairs form transient nanoscopic substructures in the liquid-ordered phase. The presented approach to study membrane heterogeneity is universal and can be applied to more realistic lipid mixtures, offering the possibility to discern differences between the structures of ordered and disordered phases in a cell membrane., Biological membranes exhibit a great deal of compositional and phase heterogeneity due to hundreds of chemically distinct components. As a result, phase separation processes in cell membranes are extremely difficult to study, especially at the molecular level. It is currently believed that the lateral membrane heterogeneity and the formation of domains, or rafts, are driven by lipid–lipid and lipid–protein interactions. Nevertheless, the underlying mechanisms regulating membrane heterogeneity remain poorly understood. In the present work, we combine inelastic X-ray scattering with molecular dynamics simulations to provide direct evidence for the existence of strongly coupled transient lipid pairs. These lipid pairs manifest themselves experimentally through optical vibrational (a.k.a. phononic) modes observed in binary (1,2-dipalmitoyl-sn-glycero-3-phosphocholine [DPPC]–cholesterol) and ternary (DPPC–1,2-dioleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-glycero-3-phosphocholine [DOPC/POPC]–cholesterol) systems. The existence of a phononic gap in these vibrational modes is a direct result of the finite size of patches formed by these lipid pairs. The observation of lipid pairs provides a spatial (subnanometer) and temporal (subnanosecond) window into the lipid–lipid interactions in complex mixtures of saturated/unsaturated lipids and cholesterol. Our findings represent a step toward understanding the lateral organization and dynamics of membrane domains using a well-validated probe with a high spatial and temporal resolution.

In recent years, responsive polymer-based structures have been studied extensively due to their unique ability to alter their physical properties upon exposure to external stimuli. Despite this, the nanoscale Q-resolved dynamic properties of these materials have barely been explored, which is limiting the development and applications of these materials. To address this issue, we used inelastic X-ray scattering (IXS) and found evidence for van der Waals mediated molecular vibration-responsive rattling dynamics in bulk poly(isoprene-block-styrene) (SI) and poly(styrene-block-ethylene oxide) (SO) stacked thin film block copolymers. Their cylinder-forming hexagonally arranged static structures were characterized using small-angle X-ray scattering (SAXS) and grazing incidence small-angle X-ray scattering (GISAXS), complemented by scanning electron microscopy (SEM). Specifically, we observed that the longitudinal vibrational mode in bulk SI experiences a strong phonon attenuation as temperature increases from 3...

The control of phonon propagation in nanoparticle arrays is one of the new frontiers of nanotechnology, potentially enabling the discovery of materials with unknown functionalities for potential innovative applications. The exploration of the terahertz window appears quite promising as phonons in this range are the leading carriers of heat transport in insulators and their control is the key to implement devices for heat flow management. Unfortunately, this scientific field is still in its infancy and even a basic topic such as the influence of floating nanoparticles on the terahertz phonon propagation of a colloidal suspension still eludes a firm answer. Shedding some light on this topic is the main motivation of the present work, which focuses an Inelastic X-Ray Scattering (IXS) measurements on a dilute suspension of Au nano-spheres in water. Measured spectra showed a non-trivial and unexpected shape displaying multiple inelastic features that, based on a Bayesian inference analysis, we assign to phonon modes propagating throughout the nanoparticle interior. Surprisingly, the spectra bear no evidence of propagating modes, which are known to dominate the spectrum of pure water, owing to the scattering that these modes suffer from the sparse nanoparticles in suspension. In perspective, this finding may inspire simple routes to manipulate high-frequency acoustic propagation in hybrid - liquid and solid- materials.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi2Sr2CaCu2O8+δ (Bi-2212, with δ = 0.1). The morphology of the ribbon-like phase evolves simultaneously with the dome-shaped TC behavior under pressure. X-ray absorption studies show that the increasing of TC is associated with oxygen-hole redistribution in the CuO2 plan, while TC starts to decrease with pressure when oxygen holes become immobile. Additional X-ray irradiation experiments reveal that nanoscaled short-range ordering of oxygen vacancies could further lower TC, which indicates that the optimal TC is affected not only by an optimal morphology of the ribbon phase, but also an optimal distribution of oxygen vacancies. Our studies thereby provide for the first time compelling experimental e...

The investigation of phononic collective excitations in soft matter systems at the molecular scale has always been challenging due to limitations of experimental techniques in resolving low-energy modes. Recent advances in inelastic X-ray scattering (IXS) enabled the study of such systems with unprecedented spectral contrast at meV excitation energies. In particular, it has become possible to shed light on the low-energy collective motions in materials whose morphology and phase behavior can easily be manipulated, such as mesogenic systems. The understanding of collective mode behavior with a Q-dependence is the key to implement heat management based on the control of a sample structure. The latter has great potential for a large number of energy-inspired innovations. As a first step toward this goal, we carried out high contrast IXS measurements on a liquid crystal sample, D7AOB, which exhibits solid-like dynamic features, such as the coexistence of longitudinal and transverse phononic modes. For the first time, we found that these terahertz phononic excitations persist in the crystal, smectic A, and isotropic phases. Furthermore, the intermediate smectic A phase is shown to support a van der Waals-mediated nonhydrodynamic mode with an optical-like phononic behavior. The tunability of the collective excitations at nanometer-terahertz scales via selection of the sample mesogenic phase represents a new opportunity to manipulate optomechanical properties of soft metamaterials.

Newly developed 3D reconstruction technology has many uses ranging from facial recognition, self-driving vehicles, and producing accurate models of samples. To utilize 3D reconstruction, a depth map of the sample must be generated from a series of images. This can be done using stereoscopic 3D, or in the case of a fixed camera (such as the 10ID On-Axis Microscope at NSLS-II used for this paper) through focus stacking. This paper will explain how focus stacking can be used to generate in-focus images at very shallow depth of fields, and merge these images to create depth maps and 3D models.

In this work we report on terahertz phononic excitations in two-dimensional (2D) gold nanoparticle arrays in a water matrix through a series of large-scale molecular dynamics simulations. For the first time, we observe acoustic Dirac-like crossings in H (H2O) atomic (molecular) networks that emerge due to an intraband phononic scattering. These crossings are the phononic fingerprints of ice-like arrangements of H (H2O) atomic (molecular) networks at nanometer scale. We reveal how phononic excitations in metallic nanoparticles and the water matrix reciprocally impact on one another providing the mechanism for the THz phononics manipulation via structural engineering. Furthermore, we show that by tuning the arrangement of 2D gold nanoparticle assemblies, the Au phononic polarizations experience subterahertz hybridization (Kohn anomaly) due to surface electron–phonon relaxation processes. This opens the way for the sound control and manipulation in soft matter metamaterials at nanoscale.

The construction and characterization of a focusing X-ray spherical analyzer based on α-quartz 4{\bar 4}04 are presented. The performance of the analyzer was demonstrated by applying it to a high-resolution X-ray spectroscopy study of theKα1,2emission spectrum of Ni. An analytical representation based on physical grounds was assumed to model the shape of the X-ray emission lines. Satellite structures assigned to 3dspectator hole transitions were resolved and determined as well as their relative contribution to the emission spectrum. The present results on 1s−13d−1shake probabilities support a recently proposed calculation framework based on a multi-configuration atomic model.

One challenge in studying high-temperature superconductivity (HTSC) stems from a lack of direct experimental evidence linking lattice inhomogeneity and superconductivity. Here, we apply synchrotron hard X-ray nanoimaging and small-angle scattering to reveal a novel micron-scaled ribbon phase in optimally doped Bi

It has been widely accepted that the thermally excited motions of the molecules in a cell membrane is the prerequisite for a cell to carry its biological functions. On the other hand, the detailed mapping of the ultrafast picosecond single-molecule and the collective lipid dynamics in a cell membrane remains rather elusive. Here, we report all-atom molecular dynamics simulations of a 1,2-dipalmitoyl-sn-glycero-3-phosphocholine bilayer over a wide range of temperature. We elucidate a molecular mechanism underlying the lateral lipid diffusion in a cell membrane across the gel, rippled, and liquid phases using an analysis of the longitudinal and transverse current correlation spectra, the velocity auto-correlation functions, and the molecules mean square displacements. The molecular mechanism is based on the anomalous ultrafast vibrational properties of lipid molecules at the viscous-to-elastic crossover. The macroscopic lipid diffusion coefficients predicted by the proposed diffusion model are in a good agreement with experimentally observed values. Furthermore, we unveil the role of water confined at the water-lipid interface in triggering collective vibrations in a lipid bilayer.

We introduce a unified approach to states of matter (solid, liquid and gas) and describe the thermodynamics of the pressure-temperature phase diagram in terms of phonon excitations. We derive the effective Hamiltonian with low-energy cutoff in two transverse phonon polarizations (phononic band gaps) by breaking the symmetry in phonon interactions. Further, we construct the statistical mechanics of states of aggregation employing the Debye approximation. The introduced formalism covers the Debye theory of solids, the phonon theory of liquids, and thermodynamic limits such as the Dulong-Petit thermodynamic limit, the ideal gas limit and the new thermodynamic limit, dubbed here the Frenkel line thermodynamic limit. We discuss the phonon propagation and localization effects in liquids above and below the Frenkel line, and explain the "fast sound" phenomenon. As a test for our theory we calculate velocity-velocity autocorrelation and pair distribution functions within the Green-Kubo formalism. We show the consistency between dynamics of phonons and pair correlations in the framework of the unified approach. New directions towards advancements in phononic band gaps engineering, hypersound manipulation technologies and exploration of exotic behaviour of fluids relevant to geo- and planetary sciences are discussed. The presented results are equally important both for practical implications and for fundamental research., Comment: 21 pages, 7 figures, 3 tables

Nearly two decades of thorough inelastic X-ray scattering (IXS) studies of transverse-like excitation in the spectrum of simple amorphous materials are reviewed. Particular attention is given to the case of liquid water and other prototypical samples, through discussion of both solved and still open issues. The perspectives opened up by the development of next generation IXS instruments with unprecedented contrast and resolution bandwidth are briefly illustrated.

In this work, we report on inelastic X-ray scattering experiments combined with the molecular dynamics simulations on deeply supercritical Ar. The presented results unveil the mechanism and regimes of sound propagation in the liquid matter and provide compelling evidence for the adiabatic-to-isothermal longitudinal sound propagation transition. We introduce a Hamiltonian predicting low-frequency transverse sound propagation gaps, which is confirmed by experimental findings and molecular dynamics calculations. As a result, a universal link is established between the positive sound dispersion (PSD) phenomenon and the origin of transverse sound propagation revealing the viscous-to-elastic crossover in liquids. The PSD and transverse phononic excitations evolve consistently with theoretical predictions. Both can be considered as a universal fingerprint of the dynamic response of a liquid, which is also observable in a subdomain of supercritical phase. The simultaneous disappearance of both these effects at elevated temperatures is a manifestation of the Frenkel line. We expect that these findings will advance the current understanding of fluids under extreme thermodynamic conditions., Comment: 18 pages, 5 figures

Knowledge of the high-pressure behavior of carbon dioxide (CO2), an important planetary material found in Venus, Earth, and Mars, is vital to the study of the evolution and dynamics of the planetary interiors as well as to the fundamental understanding of the C-O bonding and interaction between the molecules. Recent studies have revealed a number of crystalline polymorphs (CO2-I to -VII) and an amorphous phase under high pressure-temperature conditions. Nevertheless, the reported phase stability field and transition pressures at room temperature are poorly defined, especially for the amorphous phase. Here we shed light on the successive pressure-induced local structural changes and the molecular-to-nonmolecular transition of CO2 at room temperature by performing an in situ study of the local electronic structure using X-ray Raman scattering, aided by first-principle exciton calculations. We show that the transition from CO2-I to CO2-III was initiated at around 7.4 GPa, and completed at about 17 GPa. The present study also shows that at ~37 GPa, molecular CO2 starts to polymerize to an extended structure with fourfold coordinated carbon and minor CO3 and CO-like species. The observed pressure is more than 10 GPa below previously reported. The disappearance of the minority species at 63(± 3) GPa suggests that a previously unknown phase transition within the nonmolecular phase of CO2 has occurred.

High-quality quartz (α-SiO2) crystals are characterized, and their use for inelastic X-ray scattering analyzers is presented and discussed., Spherical analyzers are well known instruments for inelastic X-ray scattering (IXS) experiments. High-resolution IXS experiments almost always use Si single crystals as monochromators and spherical analyzers. At higher energies (>20 keV) Si shows a high energy resolution (

A concept of an inelastic x-ray scattering (IXS) spectrograph with an imaging analyzer was proposed recently and discussed in a number of publications (see e.g. Ref.1). The imaging analyzer as proposed combines x-ray lenses with highly dispersive crystal optics. It allows conversion of the x-ray energy spectrum into a spatial image with very high energy resolution. However, the presented theoretical analysis of the spectrograph did not take into account details of the scattered radiation source, i.e. sample, and its impact on the spectrograph performance. Using numerical simulations we investigated the influence of the finite sample thickness, the scattering angle and the incident energy detuning on the analyzer image and the ultimate resolution.

Commissioning of the first X-ray beamlines of NSLS-II included detailed measurements of spectral and spatial distributions of the radiation at different locations of the beamlines, from front-ends to sample positions. Comparison of some of these measurement results with high-accuracy calculations of synchrotron (undulator) emission and wavefront propagation through X-ray transport optics, performed using SRW code, is presented.

A novel on-axis X-ray microscope with 3 µm resolution, 3x magnification, and a working distance of 600 mm for in-situ sample alignment and X-ray beam visualization for the Inelastic X-ray Scattering (IXS) beamline at NSLS-II is presented. The microscope uses reflective optics, which minimizes dispersion, and allows imaging from Ultraviolet (UV) to Infrared (IR) with specifically chosen objective components (coatings, etc.). Additionally, a portable high resolution X-ray microscope for KB mirror alignment and X-ray beam characterization was developed.

The passive transport of molecules through a cell membrane relies on thermal motions of the lipids. However, the nature of transmembrane transport and the precise mechanism remain elusive and call for a comprehensive study of phonon excitations. Here we report a high resolution inelastic X-ray scattering study of the in-plane phonon excitations in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine above and below the main transition temperature. In the gel phase, for the first time, we observe low-frequency transverse modes, which exhibit a phonon gap when the lipid transitions into the fluid phase. We argue that the phonon gap signifies the formation of short-lived nanometre-scale lipid clusters and transient pores, which facilitate the passive molecular transport across the bilayer plane. Our findings suggest that the phononic motion of the hydrocarbon tails provides an effective mechanism of passive transport, and illustrate the importance of the collective dynamics of biomembranes., The molecular transport through bio-membranes of cells heavily relies on the dynamics of lipids, but the related mechanism remains unknown. Here, Zhernenkov et al. observe the propagating transverse phonon mode with a finite band gap and suggest its connection to short-lived local lipid clustering.

The principles of the virtual source spread (spatial broadening) phenomenon induced by angular dispersion in asymmetric X-ray Bragg reflections are illustrated, from which the virtual source properties are analyzed for typical high-resolution multiple-crystal monochromators, including inline four-bounce dispersive monochromators, back-reflection-dispersion monochromators and nondispersive nested channel-cut monochromators. It is found that dispersive monochromators can produce spread virtual sources of a few millimetres in size, which may prevent efficient microfocusing of the beam as required by inelastic X-ray scattering spectroscopy and other applications. Possible schemes to mitigate this problem are discussed. The analyses may provide important guidelines for designing and optimizing modern high-precision synchrotron X-ray optics and beamline instrumentation for spectroscopy, imaging and nanofocusing applications.

There are still large discrepancies among the previous reports on the spin transition of iron in Mg–perovskite (Pv). To alleviate this problem, we examined the spin state of Fe3 + in Mg0.85Fe3 +0.15Al0.15Si0.85O3 Pv up to 200 GPa by X-ray emission spectroscopy (XES) and X-ray diffraction (XRD). The gradual decrease of the high spin (HS) ratio of Fe3 + by low temperature annealing of the samples above ~ 60 GPa in XES and the change of the trend of unit cell volumes with pressure by annealing at 50–60 GPa in XRD indicate that Fe3 + occupies the A-site and is HS below ~ 50 GPa but above 50–60 GPa it gradually replaces Al at the B-site through cation exchange reaction by annealing and becomes low spin (LS), while Fe3 + remaining at the A-site is HS up to 200 GPa. This means that the spin state of Fe3 + depends on Fe3 + occupancies between the A- and B-sites and these Fe3 + occupancies are strongly controlled by the synthesis condition and annealing temperature of the samples through the cation exchange reaction. The present results combined with the previous reports indicate that in Al-bearing Mg–Pv in the lower mantle Fe2 + occupies the A-site and remains HS for the whole lower mantle, while Fe3 + occupies the A-site and is HS below ~ 50 GPa but above 50–60 GPa it replaces Al at the B-site and becomes LS, on the assumption that spin transition pressure of Fe2 + at the A-site is higher than that of Fe3 + at the same site.

Characterization and testing of an L-shaped laterally graded multilayer mirror are presented. This mirror is designed as a two-dimensional collimating optics for the analyzer system of the ultra-high-resolution inelastic X-ray scattering (IXS) spectrometer at National Synchrotron Light Source II (NSLS-II). The characterization includes point-to-point reflectivity measurements, lattice parameter determination and mirror metrology (figure, slope error and roughness). The synchrotron X-ray test of the mirror was carried out reversely as a focusing device. The results show that the L-shaped laterally graded multilayer mirror is suitable to be used, with high efficiency, for the analyzer system of the IXS spectrometer at NSLS-II.

Inelastic X-ray scattering (IXS) is a general experimental technique for studying lattice and electronic excitations, which has undergone rapid development following the advent of the third generation synchrotron radiation facilities. X-ray Raman scattering (XRS) is inelastic scattering of X-rays due to the excitation associated with bound electrons in an atom. Its very small scattering cross-section is compensated for by a high-flux beam generated from a strong photon source. Instrumentation for IXS is now highly sophisticated, and has been applied to study a broad range of condensed matter systems [1].

We have performed X-ray Raman scattering (XRS) measurements on the oxygen K and silicon L absorption edges of four silica minerals: α-quartz, α-cristobalite, coesite, and stishovite. We have also calculated the partial electron densities of states (DOSs) and compared these with the XRS spectra. This study demonstrates that the short-range structure around the atom of interest strongly influences the XRS spectral features. Importantly, the oxygen K-edge XRS spectra are found to reflect the p-orbital DOS while the silicon L-edge spectra reflect the s- and d-orbital DOSs, even when a product of a momentum transfer and a mean radius of a electron orbit (1s for oxygen and 2p for silicon), Qr, is close to or larger than unity. Building on this, calculations of the partial DOSs for other silica phases are presented, including ultra-high-pressure phases, which provide a good reference for further XRS study of silica and silicate minerals. XRS measurements should be performed on not only either of oxygen or silicon but also on many kinds of constituent elements to reveal the structural change of glasses/melts of silicates under extreme conditions.

This paper describes a scheme utilizing a set of low-cost and compact Kirkpatrick–Baez mirrors for upgrading the optical system of the Taiwan Inelastic X-ray Scattering beamline at SPring-8 for high-pressure experiments using diamond-anvil cells. The scheme as implemented improves the focus to 13 µm × 16 µm with transmission of up to 72%., Inelastic X-ray scattering (IXS) is a powerful technique capable of probing the dynamic behavior and electronic structure of materials. For IXS experiments under high pressure up to the megabar range using state-of-the-art diamond-anvil-cell technology, the sample volume is limited to the order of 1 × 10−3 mm3 for which a beam focus of the same order and less is often required. In this paper a scheme utilizing a set of low-cost and compact Kirkpatrick–Baez mirrors for upgrading the existing optical system of the Taiwan IXS beamline at SPring-8 is described. The scheme as implemented improves the focus to 13 µm × 16 µm (horizontal × vertical) with a transmission of up to 72% and a flux density gain of over 30 times, which has enhanced substantially the efficiency of the beamline for high-pressure research.

Supercritical fluids play a significant role in elucidating fundamental aspects of liquid matter under extreme conditions. They have been extensively studied at pressures and temperatures relevant to various industrial applications. However, much less is known about the structural behaviour of supercritical fluids and no structural crossovers have been observed in static compression experiments in any temperature and pressure ranges beyond the critical point. The structure of supercritical state is currently perceived to be uniform everywhere on the pressure-temperature phase diagram, and to change only in a monotonic way even moving around the critical point, not only along isotherms or isobars. Conversely, we observe structural crossovers for the first time in a deeply supercritical sample through diffraction measurements in a diamond anvil cell and discover a new thermodynamic boundary on the pressure-temperature diagram. We explain the existence of these crossovers in the framework of the phonon theory of liquids using molecular dynamics simulations. The obtained results are of prime importance since it implies a global reconsideration of the mere essence of the supercritical phase. Furthermore, this discovery may pave the way to new unexpected applications and to the exploration of exotic behaviour of confined fluids relevant to geo- and planetary sciences., 11 pages, 5 figures

A further development of a focusing monochromator concept for X-ray energy resolution of 0.1 meV and below is presented. Theoretical analysis of several optical layouts based on this concept was supported by numerical simulations performed in the “Synchrotron Radiation Workshop” software package using the physical-optics approach and careful modeling of partially-coherent synchrotron (undulator) radiation. Along with the energy resolution, the spectral shape of the energy resolution function was investigated. It was shown that under certain conditions the decay of the resolution function tails can be faster than that of the Gaussian function.

The THz spectrum of density fluctuations, $S(Q, \omega)$, of vitreous GeO$_2$ at ambient temperature was measured by inelastic x-ray scattering from ambient pressure up to pressures well beyond that of the known $\alpha$-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., Comment: 18 pages, 5 figures

In this paper we present inelastic X-ray scattering experiments in a diamond anvil cell and molecular dynamic simulations to investigate the behavior of phononic excitations in liquid Ar. The spectra calculated using molecular dynamics were found to be in a good agreement with the experimental data. Furthermore, we observe that, upon temperature increases, a low-frequency transverse phononic gap emerges while high-frequency propagating modes become evanescent at the THz scale. The effect of strong localization of a longitudinal phononic mode in the supercritical phase is observed for the first time. The evidence for the high-frequency transverse phononic gap due to the transition from an oscillatory to a ballistic dynamic regimes of motion is presented and supported by molecular dynamics simulations. This transition takes place across the Frenkel line thermodynamic limit which demarcates compressed liquid and non-compressed fluid domains on the phase diagram and is supported by calculations within the Green-Kubo phenomenological formalism. These results are crucial to advance the development of novel terahertz thermal devices, phononic lenses, mirrors, and other THz metamaterials., 8 pages, 5 figures. arXiv admin note: text overlap with arXiv:1512.07202

Up to now simulation of perfect crystal optics in the “Synchrotron Radiation Workshop” (SRW) wave-optics computer code was not available, thus hindering the accurate modelling of synchrotron radiation beamlines containing optical components with multiple-crystal arrangements, such as double-crystal monochromators and high-energy-resolution monochromators. A new module has been developed for SRW for calculating dynamical diffraction from a perfect crystal in the Bragg case. We demonstrate its successful application to the modelling of partially-coherent undulator radiation propagating through the Inelastic X-ray Scattering (IXS) beamline of the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Laboratory. The IXS beamline contains a double-crystal and a multiple-crystal highenergy- resolution monochromator, as well as complex optics such as compound refractive lenses and Kirkpatrick-Baez mirrors for the X-ray beam transport and shaping, which makes it an excellent case for benchmarking the new functionalities of the updated SRW codes. As a photon-hungry experimental technique, this case study for the IXS beamline is particularly valuable as it provides an accurate evaluation of the photon flux at the sample position, using the most advanced simulation methods and taking into account parameters of the electron beam, details of undulator source, and the crystal optics.

The ultrahigh energy resolution IXS spectrometer being developed at the National Synchrotron Light Source II (NSLSII) employs an innovative optical design. Its analyzer system utilizes an L-shaped laterally graded multilayer mirror in tandem with a multi-crystal arrangement. The multi-crystal arrangement explores the angular dispersion effect in extremely asymmetric Bragg reflections to achieve sub-meV energy resolution at an energy about 9.1 keV. Its angular acceptance (~ 0.1 mrad) is about two orders of magnitude lower than the spherically-bent backscattering analyzers conventionally used in other IXS spectrometers. The L-shaped laterally graded multiplayer mirror was designed to increase the angular acceptance of this new multi-crystal optics to a comparable level. It performs angular collimation of the incoming beam from about 15 mrad down to 0.1 mrad in both vertical and horizontal directions. Here we present simulations of the mirror performance and study the positioning and stability requirements in conjunction with the multicrystal energy analyzer.

Photons are an alternative probe to electrons or ions for the detection of surface and interface collective modes. We have used synchrotron radiation in conjunction with angle resolved photoyield measurements to study the evolution of overlayer excitation modes in thin alkali layers. Our experimental results show clear evidence of collective modes such as the multipole plasmon, bulk overlayer plasmon and threshold excitation. Both the energy and lineshape of these photoyield resonances show strong thickness dependence. The response of the hidden substrate is rather different. The Al multipole peak shows no energy shift as a function of coverage confirming the absence of an intermediate charge density. We discuss our results in terms of previous dynamical calculations of the surface response.

Angle-resolved photoemission has proven to be a powerful tool, especially in combination with polarized, tunable light produced by synchrotron radiation, for the study of the electronic structure of a wide range of materials. Its intrinsic surface sensitivity makes it an ideal choice for addressing some issues of current interest in surface science, among which are the electronic structure of metal-oxide thin films and the effects of electron-phonon interaction in simple, two-dimensional metallic systems. After a brief introduction of the technique of angle-resolved photoemission and the properties of synchrotron radiation, examples are given to illustrate some current activities in these areas. In particular, the electronic structure of an iron-oxide thin film, namely, Fe_3O_4(111) epitaxially grown on Pt(111), and the effects of strong electron-phonon interaction on α-Ga(010) surface and its link with a phase transition on the surface will be described and discussed., この論文は国立情報学研究所の電子図書館事業により電子化されました。

We have investigated the (010) surface of $\ensuremath{\alpha}\ensuremath{-}\mathrm{Ga}$ by angle-resolved photoemission and low energy electron diffraction. We find a surface state around the $\overline{C}$ point of the surface Brillouin zone. The electron-phonon coupling at this surface is very strong with an electron-phonon mass enhancement parameter of $\ensuremath{\lambda}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1.4\ifmmode\pm\else\textpm\fi{}0.10$. Our spectra show high background intensity in a projected bulk band gap which cannot be accounted for by defect scattering and is therefore interpreted as indicating a nonquasiparticle behavior. Upon cooling the sample below 220 K we observe a phase transition accompanied by spectral changes near the Fermi level.

The circular dichroism of angle-resolved photoelectron spectra was investigated for core-levels from clean and hydrogen exposed GaAs (111) surfaces. It was found that the circular dichroism of Ga-3d and As-3d photoelectrons shows clear dependence on the emission angle of the photoelectrons and the sample surface. It is proposed that the experimental results may be interpreted primarily in terms of the interference of photoelectrons affected by the anisotropic field in the surface layer of GaAs (111).

The size dependence of the electronic structure of Pd clusters deposited on an ordered Al2O3 film on Re(0001) has been studied using angle-resolved photoemission in conjunction with synchrotron radiation. The appearance of dispersion effects along directions both parallel and perpendicular to the substrate surface with increasing cluster size is observed, which is attributed to the formation of crystallites with a preferred orientation and signifies the non-metal to metal transition of the Pd clusters. The transition appears to take place at an estimated average cluster size of approximately 25 A.

The electronic states of O/Cs/GaAs(100) have been investigated by using ultraviolet photoelectron spectroscopy in order to understand the initial coadsorption kinetics on the way to the negative electron affinity formation. It was found that the energy positions of the Ga-3d and As-3d peaks shift to the lower binding energy side by the first Cs deposition, while they shift to the higher binding energy side during the n-th Cs deposition ( n≧3). It was also found that besides the appearance of oxidized As, the width of the Ga-3d peak becomes larger by the first oxygen exposure. In the case of the n-th Cs deposition and oxygen exposure, all photoelectron peaks and the work function made parallel shifts in energy, which can be well interpreted in terms of the change in band bending. These results indicate that the coadsorption kinetics can be classified into two stages: At first Cs deposition and oxygen exposure, both of Ga and As react with Cs and O, resulting in the rearrangement in the surface layers, whil...

A temperature-dependent study of the magnetic surface states on Ni(100) near the Fermi level reported by Plummer and Eberhardt [Phys. Rev. B 20 (1979) 1444] has been carried out using angle-resolved photoemission. The line width of the single narrow peak corresponding to a transition from the isolated surface feature of even symmetry has been found to exhibit no changes with temperature in the range from 100 to 700 K. The peak previously reported by Plummer and Eberhardt as a transition from the odd majority surface state has been resolved into majority and minority components at room temperature half-way along the \ gGM direction. These components have been observed to move towards each other with increasing temperature and are no longer resolvable above 400 K. The width of the single peak for temperatures at and above the Curie temperature (Tc) suggests, however, a non-vanishing exchange splitting above Tc, indicative of short-range magnetic order.

Sagittal focusing is a widely used geometry to horizontally focus X-rays in synchrotron beamlines. Usually, two types of devices are used: toroidal mirrors combined with flat X-ray monochromators or flat mirrors combined with sagittal focusing monochromators. The former option seems to be better since the stresses caused by the bending of the second crystal in a double crystal monochromator (DCM) are avoided. In this work we explore the effect of sagittal focusing in medium to high energy resolution X-ray monochromators. Our studies are based on a theoretical explanation of experimental data acquired in two different experiments performed at the XRD2 beamline at Laboratorio Nacional de Luz Sincrotron (LNLS / Brazilian Synchrotron) and X18A at the National Synchrotron Light Source (NSLS / BNL / USA). The first experiment was carried out with a flat meridional bendable mirror followed by a DCM with the second crystal being sagitally bent. The second experiment was carried out with a flat Si 111 DCM followed by a toroidal, but meridional bendable mirror. Both setups are completed by a Si 551 4-bounce monochromator to scan the energy spectrum around 13.7 keV and 13.9 keV, respectively. The results show that the sagittal curvature induces an energy structure. Theoretical studies made by analyzing the reflecting angles in the mirror surface joined with the dynamical theory of X-ray diffraction in the 4-bounce X-ray monochromators confirm these results, which are also explored by the DuMond diagram.