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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.

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.

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.

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 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.

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.

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.

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.

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

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...

Studies of angle-resolved photoemission from an As-rich GaAs( 1 1 1 )-2x2 surface have been extended to off-normal emission. The experimentally observed peak dispersion was compared with calculation and to previously reported photoemission results. This enabled us to identify emission features due mainly to surface states and features to which a combination of various transitions, including surface umklapp, may contribute.

The spectral momentum density ϱ(E, q ) of the valence electrons of solid thin films of annealed amorphous carbon, amorphous silicon and silicon carbide has been measured using (e,2e) spectroscopy. Substantial contrast has been observed between the images of the three momentum densitites, which show not only well-defined energy band dispersion in the three materials, but also the antisymmetric gap due to the unequal potentials between the Si and C sites in the silicon carbide. The relation between the three momentum densities is explained within the framework of the one-electron band theory of solids.

The spectral momentum density \ensuremath{\rho}(\ensuremath{\epsilon},q) of the valence electrons of a thin polycrystalline silicon carbide (SiC) film has been measured using an (e,2e) spectrometer employing a noncoplanar asymmetric geometry with estimated energy and momentum resolutions of about 2.0 eV and 0.15 a.u., respectively. Well-defined valence-band dispersion has been observed from the measured momentum density which resembles a parabola, but deviates from what is expected for a free electron near the top of the band and at the boundary of the Brillouin zone, where the antisymmetric gap due to the unequal potentials between the Si and C sites in SiC is clearly visible. Based on the assumption that the spectral momentum density of polycrystalline materials is a spherical average of the spectral momentum density of the corresponding single crystalline phase of the materials, ab initio linear muffin-tin orbital calculations have been performed using the zinc-blende structure of \ensuremath{\beta}-SiC. The measured dispersion of the energy band is in excellent agreement with theory. Reasonable agreement is also obtained for the energy-integrated momentum density, although the measured momentum density exceeds considerably the calculated one at high momenta. The theoretical implication of using crystal band-structure calculations for studying disordered materials is also discussed.

In this paper we discuss the finite-element analysis (FEA) of a one-dimensional beryllium compound refractive lens (Be-CRL) that was undertaken to study the feasibility of installing the CRL in the Inelastic X-ray Scattering (IXS) beamline of National Synchrotron Light Source-II (NSLS-II) (a new state-of-the-art medium-energy third-generation storage ring). The current insertion device for this beamline is an IVU22-6m in-vacuum planar undulator delivering a total power of ~9 kW with a peak power density of ~90 kW/mrad2. Through analysis, based on calculation of spectral angular distribution of undulator radiation from IVU22, we determined that it is essential to install a 30 µm graphite filter upstream of the CRL in order to restrict the temperature rise in the CRL to 65°C for acceptable thermal strain.

Angle-resolved photoemission techniques have been used to study the occupied band structure of the As-terminated GaAs(001)-1×1 surface grown by molecular-beam epitaxy. The measurements were taken along the [100] azimuth and covered the photon-energy range 10-70 eV. Structure plots involving linear-muffin-tin-orbital (LMTO) calculated valence bands and free-electron-like final states (FELFS's) were used to interpret the acquired data, which included normal-emission spectra at various photon energies and off-normal-emission spectra at selected photon energies

The iron structural and magnetic transition between the magnetic (bcc-$\ensuremath{\alpha})$ and the nonmagnetic (hcp-$\ensuremath{\epsilon})$ phases has been studied monitoring the pressure dependence of the Fe-$K\ensuremath{\beta}$ fluorescence line excited with monochromatic synchrotron radiation. The relative intensity of the two multiplets shows an S-shaped pressure curve with flex point at the known transition pressure of 130 kbar. The S width of $\ensuremath{\approx}30$ kbar also coincides with the one determined in structural determinations, and in magnetism studies using M\"ossbauer techniques. This shows how the x-ray emission method can be used to probe the local magnetic properties of atoms under extreme thermodynamic conditions.

Near-edge x-ray Raman scattering (XRS) spectra of the silicon $L$ edge have been obtained on ${\text{SiO}}_{2}$ glass under compression in a diamond anvil cell up to 74 GPa. Partial densities of states (DOS's) of electrons, which the spectra reflect, have been calculated. The spectra for the glass do not show significant variations with pressure, whereas distinct differences are observed between quartz and stishovite, providing clear evidence for the nonexistence of sixfold-coordinated silicon by oxygen, that is stishovitelike silicon, in silica glass up to 74 GPa. A post main-edge hump, which is not seen in the XRS spectra and DOS's of quartz and stishovite, and an edge energy shift suggest that the silicon is in a different coordination environment under pressure. A compression mechanism of ${\text{SiO}}_{2}$ glass which involves the formation of fivefold-coordinated silicon following the decrease in Si-O-Si angle is proposed to explain the observed changes up to 74 GPa.

Knowledge of the electronic structure of amorphous and liquid silica at high pressures is essential to understanding their complex properties ranging from silica melt in magma to silica glass in optics, electronics, and material science. Here we present oxygen near $K$-edge spectra of ${\mathrm{SiO}}_{2}$ glass to $51\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ obtained using x-ray Raman scattering in a diamond-anvil cell. The x-ray Raman spectra below $\ensuremath{\sim}10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ are consistent with those of quartz and coesite, whereas the spectra above $\ensuremath{\sim}22\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ are similar to that of stishovite. This pressure-induced spectral change indicates an electronic bonding transition occurring from a fourfold quartzlike to a sixfold stishovitelike configuration in ${\mathrm{SiO}}_{2}$ glass between $10\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ and $22\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. In contrast to the irreversible densification, the electronic bonding transition is reversible upon decompression. The observed reversible bonding transition and irreversible densification call for a coherent understanding of the transformation mechanism in compressed ${\mathrm{SiO}}_{2}$ glass.

The electronic structure of thulium monochalcogenides $\mathrm{Tm}X$ $(X=\mathrm{S},\mathrm{Se},\mathrm{Te})$ is investigated by x-ray absorption spectroscopy (XAS) in the partial fluorescence yield mode (PFY-XAS) and resonant x-ray emission spectroscopy around and far below the edge. These three resonant inelastic x-ray scattering (RIXS)-derived techniques yield consistent values of the thulium valency of 2.67, 2.65, and 2.70, respectively, in the mixed-valent compound TmSe. These values are in closer agreement with the valency derived from the lattice parameter measurement compared to previous x-ray photoemission spectroscopy and XAS studies. The study demonstrates that RIXS is a powerful and accurate probe of mixed-valent states in $f$-electron systems.

The near K-edge structure of oxygen in liquid water and ices III, II, and IX at 0.25 GPa and several low temperatures down to 4 K has been studied using inelastic x-ray scattering at 9884.7 eV with a total energy resolution of 305 and 175 meV. A marked decrease of the preedge intensity from the liquid phase and ice III to ices II and IX is attributed to ordering of the hydrogen bonds in the proton-ordered lattice of the latter phases. Density functional theory calculations including the influence of the Madelung potential of the ice IX crystal correctly account for the remaining preedge feature. Furthermore, we obtain spectroscopic evidence suggesting a possible new phase of ice at temperatures between 4 and 50 K.

Crystal analyzers produced by spherically bending a Si crystal wafer are employed in high‐resolution inelastic x‐ray scattering experiments to increase the counting efficiency. The fabrication commonly involves dicing the crystal wafer into blocks of ∼1mm×1mm to release the bending strain before gluing the wafer onto a spherical substrate. During the gluing, the relative alignment of each block must be maintained to achieve the desired focusing effect. A novel pressing tool has been designed to apply uniform pressure on the wafer during the gluing process to ensure the relative alignment between the crystal blocks, and has produced analyzers with satisfactory performance. The design details and the fabrication process will be presented and discussed.

Spherically bent silicon crystal x-ray analyzers have been employed in high-resolution inelastic x-ray scattering experiments to increase the counting efficiency due to the small cross-section of the inelastic scattering processes of interest. [1] In these bent analyzers, strain causes a distribution of lattice spacing, limiting the achievable energy resolution. Hence, the silicon wafers were diced using precision diamond saws into an array of ~1x1 mm2 blocks, and then acid etched to remove the saw damage, leaving blocks ~0.6x0.6 mm2 glued to a spherical concave substrate. With this method, meV energy resolution has been demonstrated with a bending radius of 6.5 m. [2] We seek to optimize the dicing process using the technique of deep reactive ion etching (DRIE) to develop highly efficient crystal analyzers. Ideally, each individual block subtends an angle that matches the acceptance (Darwin width) of the silicon reflection. This requires block sizes of about 500 μm2. DRIE offers the flexibility of selecting the block size, with finely controlled groove widths (i.e., minimal loss of material), and hence the possibility of controlling the energy width. We have made a prototype analyzer using DRIE with block size of 470 μm2, groove widths of 30 μm, and about 500 μm deep. The wafer was then bent and glued to a glass substrate with 2-meter radius. Tests showed encouraging results, with the DRIE analyzer performing at the 100 meV level. Details of the process and further refinements will be discussed.

We have studied the growth and magnetism of two-dimensionally coupled nanometer-scale Co dots which are squarely arranged on a $\mathrm{Cu}(001)\ensuremath{-}c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ surface. The morphology was analyzed by scanning tunneling microscopy, and the magnetization was studied using the magneto-optical Kerr effect. Well-ordered arrays of two monolayer (ML) thick Co dots interconnected by narrow 1 ML thick Co films can be grown by adjusting the deposited amount of Co. Here we used selective growth of Co at the clean Cu area of the surface, which consists of $5\ifmmode\times\else\texttimes\fi{}5 {\mathrm{nm}}^{2}$ N-adsorbed $c(2\ifmmode\times\else\texttimes\fi{}2)$ patches separated by clean Cu lines of a few nm in width. The observed ferromagnetism in these arrays is considered to be mediated by narrow monolayer thick Co films on clean Cu lines. When the average thickness of Co exceeds 1.5 ML, 2 ML thick Co dots are connected with each other, and 1 ML Co films grow on the $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ patches. For Co films with an average thickness between 1.8 ML and 2.1 ML, the magnetization is almost constant between 150 K and 370 K, and increases with decreasing temperature from 150 K. This result suggests that polarization is induced in the 1 ML Co film on $c(2\ifmmode\times\else\texttimes\fi{}2)\mathrm{N}$ patches below 150 K.

We report on the electronic structure and the valence of Tm in TmTe studied under high pressure by X-ray absorption spectroscopy in the partial fluorescence yield mode (PFY-XAS). The pressure-dependent behavior of the Tm valence v can be divided into three regimes: (i) in the 0–3 GPa range Tm remains mostly divalent; (ii) in the 3–4.5 GPa range v rapidly increases up to 2.45; (iii) in the 4.5–10.6 GPa range v increases more gently up to 2.85. The variations of v in these regimes are consistent with previous compressibility data, though the pressure ranges slightly differ between both studies. More interestingly, our results shed new light on the highest pressure regime, where Tm still has not reached a full trivalent state unlike commonly accepted ideas.

Recent developments in (e,2e) momentum spectroscopy of thin films have resulted in the study of a diverse range of solid targets. These studies have revealed the electronic structure of solids in much more detail than has been previously available using this technique. A summary of the developments which have led up to this is presented here. Some details of a spectrometer that represents the state of the art are given. Recent results from this spectrometer are discussed.

This paper discusses measurement of the band structure of a semiconductor, GaAs, and the Fermi surface of Copper determined from angle resolved photoemission measurements. The dissimilarity in the materials and the information derived is not as divergent as may first appear. The measurements techniques are identical, the methods of interpretation are similar, both provide information of bulk electronic states and anyway, the Fermi surface is way of describing aspects band structure.

The ultrahigh resolution IXS beamline of NSLS-II is designed to probe a region of dynamic response that requires an ultrahigh energy and momentum resolution of up to 0.1 meV and < 0.1 nm -1 , respectively, which is currently still beyond the reach of existing low and high frequency inelastic scattering probes. Recent advances at NSLS-II in developing the required x-ray optics and instrumentation based on the use of extremely asymmetric Bragg back reflections of Si have allowed us to achieve sub-meV energy resolution with sharp tails and high efficiency at a medium energy of around 9.1 keV, thereby validating the optical design of the beamline for the baseline scope and paving the way for further development towards the ultimate goal of 0.1 meV. The IXS beamline is expected to provide a broad range of scientific opportunities, particularly in areas of liquid, disordered and bio-molecular systems.

The Mn 3d valence states in single-crystalline TbMnO3 were probed using x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The polarized Mn K-edge x-ray absorption spectra show a strong polarization dependence, particularly for the white line region, indicating the strong anisotropic Mn–O bonding within the ab plane in TbMnO3. The RXES data obtained at the Mn K edge clearly reveal that unoccupied Mn 3d states exhibit a relatively delocalized character, stemming from hybridization of the Mn 3d states with the neighboring Mn 4p orbitals. The authors demonstrated that resonant x-ray emission spectroscopy is able to characterize the degree of localization of the unoccupied states or hole carriers in manganites.

The photon-excited multipole plasmon and the bulklike plasmon modes have been studied in Na/Al(111) and K/Al(111). These collective modes appear for a coverage of ≥2 monolayers. Both the multipole and the bulklike plasmon modes exhibit interesting variations in frequency, line shape, and relative intensity with adlayer coverage. The reasons for such behavior are discussed on the basis of existing theoretical results. The substrate Al multipole plasmon is found to be attenuated by smooth adlayer growth. Deposition of K on two monolayer Na/Al(111) results in the growth of K related collective excitation at the expense of the Na modes. For complicated surface structures like Al(111)-(√3×√3)R30°:K or the Al(111)-(2×2):Na surface alloy, electron charge-density profiles at the surface are calculated based on ab initio density-functional theory-local-density approximation method to explain the photoyield data. The importance of the shape of the charge-density profile in determining the collective excitations is demonstrated. For Al(111)-(√3×√3)R30°:K, a strong increase in intensity in the energy region of the K plasmons is observed in the on-top structure which is attributed to a "mixed plasmon" mode. These results show that while the experimental observations for smooth alkali-metal adlayers are in good agreement with existing theory, more theoretical work, especially for the complicated surface structures, is desirable.