Combination Of Synchrotron Radiation Research Articles

X-ray diffractometer combining synchrotron radiation and pulsed magnetic fields up to 40 T

A synchrotron X-ray diffractometer incorporating a pulsed field magnet for high fields up to 40 T has been developed and a detailed description of this instrument is reported. The pulsed field magnet is composed of two coaxial coils with a gap of 3 mm at the mid-plane for passage of the X-rays. The pixel detector PILATUS 100K is used to store the diffracted X-rays. As a test of this instrument, X-ray diffraction by a powder sample of the antiferromagnet CoO is measured below the Néel temperature. A field-dependent lattice distortion of CoO due to magnetostriction is observed up to 38 T.

Protein Structure and Function in the Time-Domain of Vibrational Spectroscopies. The Promising Applications of IR Synchrotron Radiation Micro-Spectroscopy

Fourier Transform Infrared (FTIR) spectroscopy is a fundamental technique capable to characterize proteins and to investigate their conformation and dynamics in real physiological environments. Actually, a FTIR spectrum is characterized by many features, which may be correlated to the different components of the protein structure. In the last decade many relevant results have been achieved with this technique in terms of chemical imaging of proteins at subcellular level and in the investigation of cooperative phenomena. This contribution presents a few examples that illustrate the capability of the FTIR spectroscopy to investigate both protein structure and function and the opportunities offered by IR synchrotron radiation sources. Indeed the high source brilliance of these sources enables FTIR micro-spectroscopy to be performed with spatial and time resolution not available with standard sources. Moreover, the combination of synchrotron radiation and new two-dimensional detectors open new opportunities to investigate in the IR energy domain different protein processes in real time and with proteins in their native environments.

Anisotropy in ordered sexithiophene thin films studied by angle-resolved photoemission using combined laser and synchrotron radiation

We present angle-resolved photoemission (PE) spectra of ordered multilayer sexithiophene (6T) films, 200nm thick, grown on a Au(110) single crystal. However, the measurement of sharp and nonshifted PE spectral features from the low-conducting organic material is only possible if the positive surface charge, generated in the PE process, is fully compensated. We have accomplished this by simultaneous laser irradiation. On the basis of the resulting data we found that for these thick films the 6T molecules are preferentially oriented with their long axes nearly normal to the surface.

Experimental and theoretical NEXAFS/XPS study of the room-temperature adsorption of acetonitrile onSi(001)−2×1

Combining synchrotron radiation N $1s$ x-ray photoemission and x-ray absorption spectroscopy to density functional theory calculations of electron transition energies and cross sections performed on silicon clusters, we have re-examined the issue of acetonitrile adsorption on single- and two-domain $\mathrm{Si}(001)\text{\ensuremath{-}}2\ifmmode\times\else\texttimes\fi{}1$ surfaces, taking into consideration the various adsorption models proposed in the recent theoretical works. It is shown that at 300 K and saturation coverage, the molecule is chemisorbed both under nondissociated and dissociated forms. The nondissociative adsorption mode results from a $\mathrm{di}\text{\ensuremath{-}}\ensuremath{\sigma}$ bonding involving the cyano group. The use of a vicinal surface allows us to show that the side-on (a cycloadditionlike product on the Si dimer) is the majority species of $\mathrm{di}\text{\ensuremath{-}}\ensuremath{\sigma}$ type. The datively bonded molecule (end-on) is not observed at 300 K. The molecule also dissociates on the surface, under the form of a cyanomethyl plus a silicon monohydride, a model which has not been so far proposed by theoretical works.

Two-colour studies of the even-parity autoionization series 5p51/2nℓ′(ℓ = p, f) in atomic xenon

Two-colour experiments combining synchrotron radiation and light pulses from a synchronized linear dye laser have been performed to investigate even-parity Xe* 5p5(2P1/2) np′ and nf′ resonances of atomic xenon. These autoionization states have been reached through a double-resonant excitation scheme including the short-lived intermediate states Xe* 5p5(2P3/2) 5d and 6d. Our theoretical results reproduce the experimental findings, especially the observed dramatic suppression of the np′ resonances, by taking into account strong configuration interaction in the intermediate and the final states. Moreover, theory reveals that asymmetry parameters and oscillator strengths for the 5p5nf′ and 5p5np′ series are strongly dependent on the description of the intermediate states. The measured and calculated values for the reduced widths and the quantum defects of the 5p5nf′ series are in good agreement.

Cure of Fisher rats bearing radioresistant F98 glioma treated with cis-platinum and irradiated with monochromatic synchrotron X-rays.

High-grade gliomas are usually of poor prognosis, and conventional radiotherapy, even combined with chemotherapy, still fails to improve the survival of patients. Here, we propose an innovative therapeutic approach combining synchrotron radiation with cis-diamminedichloroplatinum (II) (CDDP). As suggested previously, monochromatic synchrotron irradiation of CDDP at 78.8 keV, just above the 78.4 keV platinum absorption K-edge, leads to an enhanced photoelectric effect and an increased local toxicity. To select a particular radiation energy that could provide supra-additive effect, we used pulsed-field gel electrophoresis to assess yields of DNA double-strand breaks induced in rat F98 glioma cells after CDDP treatment combined with synchrotron X-rays. Thereafter, intracerebral CDDP injection combined with synchrotron X-rays was applied to Fisher rats bearing F98 glioma. CDDP concentrations were mapped by synchrotron X-ray microfluorescence. An extra number of more slowly repaired double strand breaks were observed when irradiating CDDP-treated F98 cells at 78.8 keV. In vivo treatments were then performed with different radiation doses and CDDP concentrations. All cell inoculations in rat brain resulted in tumor development, and tumor presence was controlled by computed tomography. Among all of the conditions tested, the combination of 3 micro g of CDDP with 15 Gy resulted in the largest median survival time (206 days). After 1 year, about 34% of treated rats were still alive. This preclinical finding, validated by molecular analysis, represents the most protracted survival reported with this radioresistant glioma model and demonstrates the interest in powerful monochromatic X-ray sources as new tools for cancer treatments.

In situ x-ray diffraction of graphite–diamond transformation using various catalysts underhigh pressures and high temperatures

In situ x-ray diffraction studies of graphite–diamond transitions with various solventcatalysts under high pressures and high temperatures at the Photon Factory and SPring-8are reviewed. By combining synchrotron radiation and a large-volume multi-anvilhigh-pressure apparatus, real-time observations have been successful in the diamondformation process with the help of various catalysts, such as transition metals, carbonatesand aqueous fluids. The experimental procedures and the technical details are described.The diffraction data with various catalysts are shown and the problems and limitations ofthis method are discussed.

X-ray fluorescence tomography of individual municipal solid waste and biomass fly ash particles.

Information about Cd distribution inside single municipal solid waste and biomass fly ash particles is fundamental since it affects its leachability. The internal 2D distributions of the main and trace elements in such highly inhomogeneous matrixes were successfully determined by means of the combined synchrotron radiation induced micro X-ray fluorescence (micro-SRXRF) and tomography (micro-SRXRFT) techniques. Scanning micro-SRXRF measurements show Cd elemental distribution within single fly ash particles to be inhomogeneous, but no information can be obtained about its internal distribution. During micro-SRXRFT analysis, single fly ash particles are successively measured by a rotational-translational scan in a VH=2 x 5 microm2 microbeam. The 2D internal elemental distribution images, obtained by the modified simultaneous algebraic reconstruction technique algorithm, provide the size and the location of Cd-containing areas together with the location of other measurable elements. Results showed Cd concentration to be higher in the core of the fly ash particles analyzed rather than on the surface of the particles. Moreover, in both ashes, Ca-containing matrixes are found to be the main Cd-bearing phases. A possible mechanism for Cd adsorption on the fly ash particles is proposed based on the obtained results.

Surface photovoltage effect and its time dependence in GaAs–GaAsP superlattice studied with combination of synchrotron and laser radiation

The surface photovoltage (SPV) effect and its temporal profiles in a GaAs–GaAsP superlattice (SL) were measured by core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser. It was found that the SPV effect in the SL is remarkably suppressed as compared with that in a bulk GaAs. The difference in the temporal profile of the SPV between SL and bulk samples was observed in microsecond range. The suppression of the SPV effect in the negative electron affinity surfaces of the SL was also observed. It is concluded that the SL with a high-doping surface layer is suitable for the spin-polarized electron source without the SPV effect.

Charge carrier dynamics at the SiO2/Si(100) surface: a time-resolved photoemission study with combined laser and synchrotron radiation

Abstract The charge carrier dynamics at a thermally grown 15 A thick SiO 2 /Si(1 0 0) interface has been studied by time-resolved Si 2p core level photoemission. Upon excitation of electron hole pairs in the surface-near region by picosecond laser pulses, the dynamics of the charge carrier recombination has been determined by time-resolved Si 2p core level photoemission via the time-dependent surface photovoltage. On a timescale from picoseconds to 800 ns a non-exponential decay of the surface photovoltage and a logarithmic dependence on laser intensity is found. Both aspects can be well described by a quasi-equilibrium model based on charge carrier dynamics which is governed by thermionic emission.

Time-resolving and energy-dispersive photoelectron detector for combined laser and synchrotron radiation experiments

A time-resolving and energy-dispersive photoelectron detector for time-resolved experiments has been set up for pump–multiple-probe experiments with combined laser and synchrotron radiation. The time resolution of the detector of about 1 ns allows an assignment of the photoelectron signal to a specific synchrotron radiation pulse for any filling pattern of third-generation synchrotron storage rings. This leads to an overall temporal resolution given by the synchrotron radiation pulse width, which is 30 ps at the synchrotron radiation facility BESSY, Berlin. Application of the pump–multiple-probe technique is demonstrated for time-resolved photoemission experiments with combined laser and synchrotron radiation.

Oxidation of Aqueous HF-treated Si(001) Surface Induced by Translational Kinetic Energy of O2 at Room Temperature

The oxidation induced by the translational kinetic energy of O2 on the Si(001) surface treated with HF solution were investigated by combining synchrotron radiation photoemission spectroscopy with the supersonic molecular beam techniques. The oxidation at room temperature did not progress up to 3600 L of O2 exposure with incident energy of 0.04 eV, whereas the oxidation states of up to Si4+ species were formed in the case of 3.0 eV. The oxide-layer thickness was estimated to be 0.26 nm at the final oxidation stages. We concluded that the Si atoms at the top layers were oxidized by the incident energy of 3.0 eV.

High pressure x-ray study on anthracene

The crystalline structure of anthracene (C14H10) under high pressure was studied performing angle dispersive x-ray diffraction experiments using synchrotron radiation in combination with Rietveld refinements and rigid body approximation. High hydrostatic pressure was applied up to 27.8 GPa using a diamond anvil cell. Full structural information (molecular orientations and lattice constants) is given up to a pressure of 20.3 GPa. At the highest pressure of 22.7 GPa the unit cell volume is decreased by 36.8%. Fourier transformation of the diffracted intensities reveals the electron density distribution within the unit cell. A pressure induced increase of the electron densities between adjacent molecules is observed. These findings are shown to be in agreement with theoretical calculations and hint towards the evolution of the anisotropic conductivity with pressure.

Dynamics of Surface Photovoltage Effects on Clean and Negative Electron Affinity Surfaces ofp-GaAs (100)

Core-level photoelectron spectroscopy with the combination of synchrotron radiation and laser light was used for exploring the dynamics of the surface photovoltage (SPV) effect on a p -GaAs (100). It was found that a temporal profile of the SPV is very different in microsecond range between room temperature and 90 K. The results can be explained with the recombination of photoexcited carriers via thermionic and tunneling processes. The SPV effects and its temporal profiles on the negative electron-affinity (NEA) surface were also studied. It was observed that the SPV effect is suppressed on the NEA surface, which may be due to the escape process of the photoexcited carriers.

The growth of silver films on Si(1 1 1)-(7 × 7) studied by using photoelectron diffraction

We have combined synchrotron radiation photoemission (PES), X-ray photoelectron diffraction (PED) and low-energy electron diffraction (LEED) to examine the formation of the Ag/Si(111)-(7×7) interface, throughout a wide silver coverage range. All studied silver films gave rise to a fcc phase with their principal crystallographic axes parallel to the substrate and a [111] orientation perpendicular to the surface. Angular-scanned PED of the Ag 4p core level showed the formation of well-ordered Ag islands, with the presence of two well-defined domains, both for 6 and 30ML films. The two domains were rotated 60° from each other and appeared in a 60/40 proportion.

The Crystal Sructure of Anthracene up to 22 GPa: a X-ray Diffraction Study

AbstractThe aim of this study is to investigate the crystalline structure of anthracene C14H10 under high pressure performing angle dispersive x-ray diffraction experiments using synchrotron radiation in combination with Rietveld refinements and rigid body approximation. High hydrostatic pressure was applied up to 27.8 GPa using a diamond anvil cell. Full structural information (molecular orientations and lattice constants) is given up to a pressure of 20.3 GPa. At the highest pressure of 22.7 GPa the unit cell volume is decreased by 36.8%. Fourier transformation of the diffracted intensities reveals the electron density distribution within the unit cell. A pressure induced increase of the electron densities between adjacent molecules is observed. These findings are shown to be in agreement with theoretical calculations and hint towards the evolution of the anisotropic conductivity with pressure.

In situ X-ray observations of phase transitions in MgAl 2 O 4 spinel to 40 GPa using multianvil apparatus with sintered diamond anvils

Phase transitions in MgAl2O4 spinel have been studied at pressures 22–38 GPa, and at temperatures up to 1600 °C, using a combination of synchrotron radiation and a multianvil apparatus with sintered diamond anvils. Spinel dissociated into a mixture of MgO plus Al2O3 at pressures to 25 GPa, while it transformed to the CaFe2O4 (calcium ferrite) structure at higher pressures via the metastably formed oxide mixture upon increasing temperature. Neither the e-phase nor the CaTi2O4-type MgAl2O4, which were reported in earlier studies using the diamond-anvil cell, were observed in the present pressure and temperature range. The zero-pressure bulk modulus of the calcium-ferrite-type MgAl2O4 was calculated as K=213 (3) GPa, which is significantly lower than that reported by Yutani et al. (1997), but is consistent with a more recent result by Funamori et al. (1998) and that estimated by an ab initio calculation by Catti (2001).

Selenium-assisted nucleic acid crystallography: use of phosphoroselenoates for MAD phasing of a DNA structure.

The combination of synchrotron radiation and a variety of atoms or ions (either covalently attached to the biomolecule prior to crystallization or soaked into crystals) that serve as anomalous scatterers constitutes a powerful tool in the X-ray crystallographer's repertoire of structure determination techniques. Phosphoroselenoates in which one of the nonbridging phosphate oxygens in the backbone is replaced by selenium offer a simplified means for introducing an anomalous scatterer into oligonucleotides by conventional solid-phase synthesis. Unlike other methods that are used to derivatize DNA or RNA by covalent attachment of a heavy atom (i.e., bromine at the C5 position of pyrimidines), tedious synthesis of specialized nucleosides is not required. Introduction of selenium is readily accomplished in solid-phase oligonucleotide synthesis by replacing the standard oxidation agent with a solution of potassium selenocyanide. This results in a diastereomeric mixture of phosphoroselenoates that can be separated by strong anion-exchange HPLC. As a test case, all 10 DNA hexamers of the sequence CGCGCG containing a single phosphoroselenoate linkage (PSe) were prepared. Crystals were grown for a subset of them, and the structure of [d(C(PSe)GCGCG)](2) was determined by the multiwavelength anomalous dispersion technique and refined to 1.1 A resolution.

SURFACE-PHOTOVOLTAGE EFFECT IN A GaAs–GaAsP SUPERLATTICE STUDIED WITH COMBINATION OF SYNCHROTRON RADIATION AND THE LASER

Core-level photoelectron spectroscopy with the combination of synchrotron radiation (SR) and a laser was used for exploring the surface-photovoltage (SPV) effect and its temporal profiles in a GaAs–GaAsP superlattice (SL). It was observed that the SPV value in the SL is suppressed as compared with a bulk GaAs. However, no significant difference was found in the temporal profile between the bulk and the SL. It is suggested that the suppression of the SPV in the SL is dominantly due to the small value of band bending under thermal equilibrium.

Pd on Cu(1 1 1) studied by photoelectron diffraction

The PdCu alloy system, which has important catalytic properties, has been the subject of many experimental and theoretical studies using a large number of different techniques. Theoretical and experimental structural studies converge in predicting ordered alloys for the Pd/Cu(1 1 0) and Pd/Cu(1 0 0) surfaces. No such agreement exists for the Pd/Cu(1 1 1) surface, however; indeed, few structural studies have been performed for this surface. Here, we report the first application of X-ray photoelectron diffraction (XPD) (using synchrotron radiation) in combination with LEED to determine the structure of ultra-thin epitaxial Pd films (∼1 ML) evaporated on Cu(1 1 1) single crystal surfaces. The analysis of the data was performed with the multiple scattering diffraction program of Chen and Van Hove. For the preparation condition used, a random surface alloy seems to form in the first three layers. The first interlayer distance expands whereas the second seems to contract.