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Resonant Auger spectra following O $1s\ensuremath{-}^{1}\ensuremath{\Pi}_{u}$ excitation of metastable oxygen $a\phantom{\rule{0.2em}{0ex}}^{1}\ensuremath{\Delta}_{g}$ molecules have been measured at high resolution under resonant Raman conditions. By selectively monitoring various decay channels, the singlet manifold excitation spectrum has been separated from the dominating triplet excitation. The decay spectra have been analyzed using the lifetime-vibrational-interference model to give the spectroscopic parameters of the $1s$ excited $^{1}\ensuremath{\Pi}_{u}$ state of ${\mathrm{O}}_{2}$. Singlet and triplet manifold Auger decay rates are also compared.

We have probed the interface of a ferromagnetic/semiconductor (FM/SC) heterojunction by a combined high resolution photoemission spectroscopy and x-ray photoelectron diffraction study. Fe/ZnSe(001) is considered as an example of a very low reactivity interface system and it expected to constitute large Tunnel Magnetoresistance devices. We focus on the interface atomic environment, on the microscopic processes of the interface formation and on the iron valence-band. We show that the Fe contact with ZnSe induces a chemical conversion of the ZnSe outermost atomic layers. The main driving force that induces this rearrangement is the requirement for a stable Fe-Se bonding at the interface and a Se monolayer that floats at the Fe growth front. The released Zn atoms are incorporated in substitution in the Fe lattice position. This formation process is independent of the ZnSe surface termination (Zn or Se). The Fe valence-band evolution indicates that the d-states at the Fermi level show up even at submonolayer Fe coverage but that the Fe bulk character is only recovered above 10 monolayers. Indeed, the Fe 1-band states, theoretically predicted to dominate the tunneling conductance of Fe/ZnSe/Fe junctions, are strongly modified at the FM/SC interface., Comment: 23 pages, 5 figures, submitted to Physical review B

A Mo-Si multilayer mirror has been used for determination of the ellipticity and higher-order content of a synchrotron beam. The method is based on the angular measure of multilayer reflectivity in the region of Bragg first- and second-order reflections. Beam parameters were derived by a fitting procedure. (c) 2006 Optical Society of America.

We report on the results obtained during the commissioning phase of the volume photoemission (VOLPE) project, now operational at ESRF. Test experiments were performed on noble metals and highly correlated systems, analyzing photoelectrons with kinetic energies up to 8 keV. They confirmed that hard X-ray photoemission spectroscopy (HAXPES) can achieve bulk sensitivity with high energy resolution (e.g. 70 meV at 6 keV kinetic energy). At these kinetic energies, the surface contribution to the measured spectra is less than 5%. (c) 2005 Elsevier B.V. All rights reserved.

Early manifestation of breast cancer is often very subtle and is displayed in a complex and variable pattern of normal anatomy that may obscure the disease. The use of dual-energy techniques, that can remove the structural noise, and contrast media, that enhance the region surrounding the tumour, could help us to improve the detectability of the lesions. The aim of this work is to investigate the use of an iodine-based contrast medium in mammography with two different double exposure techniques: K-edge subtraction mammography and temporal subtraction mammography. Both techniques have been investigated by using an ideal source, like monochromatic beams produced at a synchrotron radiation facility and a clinical digital mammography system. A dedicated three-component phantom containing cavities filled with different iodine concentrations has been developed and used for measurements. For each technique, information about the minimum iodine concentration, which provides a significant enhancement of the detectability of the pathology by minimizing the risk due to high dose and high concentration of contrast medium, has been obtained. In particular, for cavities of 5 and 8 mm in diameter filled with iodine solutions, the minimum concentration needed to obtain a contrast-to-noise ratio of 5 with a mean glandular dose of 2 mGy has been calculated. The minimum concentrations estimated with monochromatic beams and K-edge subtraction mammography are 0.9 mg ml(-1) and 1.34 mg ml(-1) for the biggest and smallest details, respectively, while for temporal subtraction mammography they are 0.84 mg ml(-1) and 1.31 mg ml(-1). With the conventional clinical system the minimum concentrations for the K-edge subtraction mammography are 4.13 mg ml(-1) (8 mm diameter) and 5.75 mg ml(-1) (5 mm diameter), while for the temporal subtraction mammography they are 1.01 mg ml(-1) (8 mm diameter) and 1.57 mg ml(-1) (5 mm diameter).

The Fe vibrational density of states (VDOS) has been determined for the heme proteins deoxymyoglobin, metmyoglobin, and cytochrome f in the oxidized and reduced states, using nuclear resonance vibrational spectroscopy (NRVS). For cytochrome f in particular, the NRVS spectrum is compared with multiwavelength resonance Raman spectra to identify those Raman modes with significant Fe displacement. Modes not seen by Raman due to optical selection rules appear in the NRVS spectrum. The mean Fe force constant extracted from the VDOS illustrates how Fe dynamics varies among these four monoheme proteins, and is correlated with oxidation and spin state trends seen in model heme compounds. The protein's contribution to Fe motion is dominant at low frequencies, where coupling to the backbone tightly constrains Fe displacements in cytochrome f, in contrast to enhanced heme flexibility in myoglobin.

We present a 5 m long spectrometer for soft x rays to be used at a synchrotron radiation beamline for resonant x-ray emission spectroscopy and resonant inelastic x-ray scattering in the 400-1600 eV energy range. It is based on a variable line spacing spherical grating (average groove density of 3200 mm(-1), R=58.55 m) and a charge coupled device two dimensional detector. With an x-ray spot on the sample of 10 mu m, the targeted resolving power is higher than 10 000 at all energies below 1100 eV and better than 7000 at 1500 eV. The off-line tests made with Al and Mg K alpha(1,2) fluorescence emissions indicate that the spectrometer can actually work at 12 000 and 17 000 resolving power at the L-3 edges of Cu (930 eV) and of Ti (470 eV), respectively. SAXES (superadvanced x-ray emission spectrometer) is mounted on a rotating platform allowing to vary the scattering angle from 25 degrees to 130 degrees. The spectrometer will be operational at the ADRESS (advanced resonant spectroscopies) beamline of the Swiss Light Source from 2007.

The normal-mode spectrum for the four-coordinated heme compound Fe(II) octaethylporphyrin, Fe(OEP), has been determined by refining force constants to the experimental Fe vibrational density of states measured with nuclear resonance vibrational spectroscopy (NRVS). Convergence of the calculated spectrum to the data was achieved by first imposing D-4 symmetry on the model structure as well as the force constants, progressively including different internal coordinates of motion, then allowing the true C-i (or S-2) point group symmetry of the C-i(1) Fe(OEP) crystal structure. The NRVS-refined normal modes are in good agreement with Raman and IR spectra at high frequencies. Prior density functional theory predictions for a model porphyrin are similar to the core modes computed with the best-fit force field, but significant differences between D-4 and C-i modes underline the sensitivity of porphyrin Fe normal modes to structural details. Some differences between the C-i best fit and the NRVS data can be attributed to intermolecular contacts not included in the normal-mode analysis.

This paper presents experimental and theoretical studies of lattice vibrations in a single-crystalline Fe3O4(001) thin film. The investigations were carried out in order to see how the lattice dynamics changes at the Verwey transition. Vibrational densities of states (DOS) were obtained from nuclear inelastic scattering (NIS) of synchrotron radiation in the temperature range 25 to 296 K, while theoretical DOS were calculated ab initio within density functional theory. Experimental phonon density of states shows good agreement with calculated DOS, reproducing both the general features of main line groups as well as the groups' structure. This is also in qualitative accord with heat capacity data, provided that experimental DOS is augmented with that calculated for oxygen atoms. We have observed a gradual change in the NIS raw data as well as the relevant DOS while lowering the temperature. In particular, the main peak in the energy region 15-25 meV shows increasing splitting on cooling. The Lamb-Mossbauer factor calculated in the course of DOS evaluation shows a pronounced drop in the vicinity of the Verwey transition that may be partly connected to the observed abrupt lowering of the count rate at approximately 7 meV for T

This paper presents experimental and theoretical studies of lattice vibrations in a single-crystalline Fe3O4(001) thin film. The investigations were carried out in order to see how the lattice dynamics changes at the Verwey transition. Vibrational densities of states (DOS) were obtained from nuclear inelastic scattering (NIS) of synchrotron radiation in the temperature range 25 to 296 K, while theoretical DOS were calculated ab initio within density functional theory. Experimental phonon density of states shows good agreement with calculated DOS, reproducing both the general features of main line groups as well as the groups' structure. This is also in qualitative accord with heat capacity data, provided that experimental DOS is augmented with that calculated for oxygen atoms. We have observed a gradual change in the NIS raw data as well as the relevant DOS while lowering the temperature. In particular, the main peak in the energy region 15-25 meV shows increasing splitting on cooling. The Lamb-Mossbauer factor calculated in the course of DOS evaluation shows a pronounced drop in the vicinity of the Verwey transition that may be partly connected to the observed abrupt lowering of the count rate at approximately 7 meV for T

We use quantitative experimental and theoretical approaches to characterize the vibrational dynamics of the Fe atom in porphyrins designed to model heme protein active sites. Nuclear resonance vibrational spectroscopy (NRVS) yields frequencies, amplitudes, and directions for 57 Fe vibrations in a series of ferrous nitrosyl porphyrins, which provide a benchmark for evaluation of quantum chemical vibrational calculations. Detailed normal mode predictions result from DFT calculations on ferrous nitrosyl tetraphenylporphyrin Fe(TPP)(NO), its cation [Fe(TPP)(NO)] + , and ferrous nitrosyl porphine Fe(P)(NO). Differing functionals lead to significant variability in the predicted Fe-NO bond length and frequency for Fe(TPP)(NO). Otherwise, quantitative comparison of calculated and measured Fe dynamics on an absolute scale reveals good overall agreement, suggesting that DFT calculations provide a reliable guide to the character of observed Fe vibrational modes. These include a series of modes involving Fe motion in the plane of the porphyrin, which are rarely identified using infrared and Raman spectroscopies. The NO binding geometry breaks the four-fold symmetry of the Fe environment, and the resulting frequency splittings of the in-plane modes predicted for Fe(TPP)(NO) agree with observations. In contrast to expectations of a simple three-body model, mode energy remains localized on the FeNO fragment for only two modes, an N-O stretch and a mode with mixed Fe-NO stretch and FeNO bend character. Bending of the FeNO unit also contributes to several of the in-plane modes, but no primary FeNO bending mode is identified for Fe(TPP)(NO). Vibrations associated with hindered rotation of the NO and heme doming are predicted at low frequencies, where Fe motion perpendicular to the heme is identified experimentally at 73 and 128 cm -1 . Identification of the latter two modes is a crucial first step toward quantifying the reactive energetics of Fe porphyrins and heme proteins.

Some sulfate-reducing and microaerophilic bacteria rely on the enzyme superoxide reductase (SOR) to eliminate the toxic superoxide anion radical (O-2.(-)). SOR catalyses the one-electron reduction Of O-2.(-) to hydrogen peroxide at a nonheme ferrous iron center. The structures of Desulfoarculus baarsii SOR (mutant E47A) alone and in complex with ferrocyanide were solved to 1.15 and 1.7 Angstrom resolution, respectively. The latter structure, the first ever reported of a complex between ferrocyanide and a protein, reveals that this organo-metallic compound entirely plugs the SOR active site, coordinating the active iron through a bent cyano bridge. The subtle structural differences between the mixed-valence and the fully reduced SOR-ferrocyanide adducts were investigated by taking advantage of the photoelectrons induced by X-rays. The results reveal that photo-reduction from Fe(III) to Fe(II) of the iron center, a very rapid process under a powerful synchrotron beam, induces an expansion of the SOR active site. ispartof: Structure vol:12 issue:9 pages:1729-1740 status: published

We have measured the photoabsorption spectra of the Kr-like ions Rb+ and Sr2+ at photon energies corresponding to the excitation of 4s-np resonances using, the dual laser plasma photoabsorption technique. Dramatic changes in the line profiles, with increasing ionization and also proceeding along the Rydberg series of each ion, are observed and explained by the trends in 4s-transition amplitudes computed within a framework of configuration-interaction Pauli-Fock calculations. Total photoionization cross sections show very good agreement with relative absorption data extracted from the measured spectra.

The high X-ray flux available at the European Synchrotron Radiation Facility (ESRF), combined with the use of a suitably designed area detector setup, allowed us to follow in real time the structural changes occurring during the template burning processes inside TS-1 and Fe-silicalite MFI zeolites with a X-ray powder diffraction technique (XRPD). Rietveld analysis of the XRPD patterns collected in the 350-1000 K interval, integrated each 15 K, yields to the determination of the template overall occupancy factor versus T with an accuracy comparable with that obtained by thermogravimetric measurements, routinely employed for this purpose. The evolution of the structural parameters (V, a, b, c, site occupancy factor of the template molecule) vs T has been obtained. These data allow us to have, for the first time, a complete view of the structural rearrangements induced by the template burning process on the zeolitic framework. The differences caused by the different heteroatom inserted in the MFI lattice (Ti or Fe) are discussed. For both TS-1 and Fe-MFI, the kinetics of the reaction were investigated, to obtain the activation energy of the calcinations process employing the nonisothermal data according to the theory recently proposed by Kennedy and Clark [Thermochim. Acta, 1997, 307, 27-35]. For TS-1 only, the time-resolved template burning experiment has been repeated in isothermal conditions at four different temperatures, to obtain the activation energy from isothermal data, according to the standard procedure. Comparison between Arrhenius plots obtained from isothermal and nonisothermal data demonstrates that the Kennedy and Clark method can be also applied to complex materials such as the MFI zeolites. This approach, when applied to time-resolved XRPD studies, is much less time consuming (requesting, in principle, one single nonisothermal run) with respect to the classic approach, which requests at least three isothermal runs. Moreover, it allows a remarkably lower associated error (151 +/- 11 versus 146 +/- 30 kJ mol(-)(1)) due to the much higher number of experimental points employed to perform the linear fit.

The vibrational spectrum of Fe-57 in chloro iron octaethylporphyrin, Fe(OEP)Cl, has been calculated by normal-mode analysis refined to absorption data from nuclear resonance vibrational spectroscopy. This technique directly measures the amplitudes and frequencies for all modes that have significant iron participation, providing rigorous constraints to the best-fit values for the force constants. The calculated normal modes reveal the importance of Fe displacements perpendicular to the heme plane for both the lowest frequency modes and the ligand modes. The actual normal modes of Fe(OEP)Cl are not well described by single modes of the core porphyrin; instead they are hybrids of multiple core modes and ethyl and chlorine displacements.

Detailed Fe vibrational spectra have been obtained for the heme model complex [Fe(TPP)(CO)-(1-Melm)] using a new, highly selective and quantitative technique, Nuclear Resonance Vibrational Spectroscopy (NRVS). This spectroscopy measures the complete vibrational density of states for iron atoms, from which normal modes can be calculated via refinement of the force constants. These data and mode assignments can reveal previously undetected vibrations and are useful for validating predictions based on optical spectroscopies and density functional theory, for example. Vibrational modes of the iron porphyrin-imidazole compound [Fe(TPP)(CO)(1-Melm)] have been determined by refining normal mode calculations to NRVS data obtained at an X-ray synchrotron source. Iron dynamics of this compound, which serves as a useful model for the active site in the six-coordinate heme protein, carbonmonoxy-myoglobin, are discussed in relation to recently determined dynamics of a five-coordinate deoxy-myoglobin model, [Fe(TPP)(2-MeHIm)]. For the first time in a six-coordinate heme system, the iron-imidazole stretch mode has been observed, at 226 cm(-1). The heme in-plane modes with large contributions from the nu(42), nu(49), nu(50), and nu(53) modes of the core porphyrin are identified. In general, the iron modes can be attributed to coupling with the porphyrin core, the CO ligand, the imidazole ring, and/or the phenyl rings. Other significant findings are the observation that the porphyrin ring peripheral substituents are strongly coupled to the iron doming mode and that the Fe-C-O tilting and bending modes are related by a negative interaction force constant.

In this work we study the adsorption of Li on a Na-intercalated TaSe2(0001) and, reversibly, the deposition of Na on a Li-intercalated TaSe2(0001) surface. The intercalation occurred by deposition of the alkali elements onto the basal plane of the TaSe2. The experiment was performed in UHV by soft Xray photoelectron spectroscopy, using synchrotron radiation as excitation source. Lithium intercalation into 1T-TaSe2 leads to a phase transition of the substrate from 1T to 2H polytypism. Lithium and sodium appear to compete in the intercalation process. Sodium pushes the preintercalated Li deeper into the bulk of the substrate, whereas, in the case of Li on Na-intercalated TaSe2, an exchange reaction takes place and part of the Na deintercalates. Surface Review and Letters

The third generation sources of soft X-rays, ALS and ELETTRA, have been producing data in surface and interface science for over two years. The impact of their ultrahigh brightness is quite evident, particularly as far as photoemission techniques are concerned. We illustrate this point with a short review of very recent examples from ELETTRA, in the specific domains of time resolution, high lateral resolution and high energy resolution.

Most of the presently known microstructures are still fabricated using silicon-based technologies. However, in the case of fabrication using anisotropic etching, geometrical limitations due to the crystallographic nature of silicon prevent the design of any in-place structure shapes. If microsystems, built by means of reactive ion etching and sacrificial layer technology do have freedom for lateral geometry, they are limited to a few micrometers height only. Nevertheless, and in spite of difficulties to always answer the demands in the best way, real microsystems are produced by these techniques and are currently present on the market. To overpass these limitations, other technologies have been studied and developed in recent years. Among them the LIGA process (German acronym for Lithography, Electroplating, Molding), which uses synchrotron radiation and in particular its hard X-Ray spectrum, is certainly the most promising one regarding to, very high aspect ratio, submicron precision, arbitrary pattering and mass production capabilities. Furthermore, LIGA can handle a large variety of materials to fabricate microsystems.

International audience; Biomolecular polyanions mainly relax by electron emission after UV excitation. Here, we study photodetachment of protein polyanions in the 6-16 eV VUV range by coupling a linear quadrupole ion trap with a synchrotron beamline. Gas-phase VUV action spectra of electrospray-produced multiply deprotonated insulin (5.6 kDa) and myoglobin (16.7 kDa) proteins are reported, which significantly increases the amount of data available on the optical response of proteins in the VUV. The influence of the protein charge and oxidation state upon the electron detachment efficiency is discussed. For small protein such as insulin, it appears that higher charge states produce higher detachment yields. Investigations on oxidized species show that the nature of the groups bearing the negative charges has an influence on the yields. For larger proteins, comparison of two forms of myoglobin clearly indicate that the three-dimensional structure does not impact much on the shape and the magnitude of the photodetachment spectra, in spite of a slight shift for the first electronic excited states. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4790165]

The Schottky-barrier formation of the Au/GaP (110) interface has been investigated by photoemission, in the presence of large surface photovoltage effects induced by the intense photon beam of a synchrotron-radiation source. The surface photovoltage has been measured with a Kelvin probe. The largest surface photovoltage shift observed in the photoemission spectra was almost 1 eV. The Schottky barrier appears to be fully established at about 8 Angstrom, while the surface photovoltage does not disappear until about 16 Angstrom. The Schottky-barrier height is 1.35+/-0.1 eV. The Kelvin-probe results demonstrate directly that the photoemission data must be corrected for the surface photovoltage during the formation of the barrier but are insensitive to it once full coverage is obtained. (C) 1996 American Vacuum Society.

Two-photon resonant photoionization of helium is investigated both experimentally and theoretically. Ground state helium atoms are excited to the 1s4p, 1s5p and 1s6p P-1 states by synchrotron radiation and ionized by a synchronized infrared pulsed picosecond laser. The photoelectron angular distributions of the emitted electrons are measured using a velocity map imaging (VMI) spectrometer. The measured asymmetry parameters of the angular distribution allow the phase differences and the ratios of the dipole matrix elements of the 1s epsilon s and 1s epsilon d channels to be determined. The experimental results agree with the calculated values obtained in a configuration-interaction calculation with a Coulomb-Sturmian basis set. The effects of the radiative decay of the intermediate state and the static electric field of the VMI spectrometer on the measurements are discussed.

The first part of this topical review provides the reader with a conceptual background sufficient to understand the mechanism of an X-FEL without using any formalism. The discussion is thus accessible to non-specialized scientists from any discipline. Then, we review the present status of selected X-FEL projects throughout the world. Examples of actual experiments are used to illustrate the potential impact of these new, exciting sources at the forefront of photon technology.

Using linear response approach to the Mossbauer isomer shift, the calibration constant alpha(Fe-57) was obtained from high level ab initio calculations carried out for a representative set of iron compounds. The importance of the effects of relativity and electron correlation for an accurate description of the Fe-57 isomer shift is demonstrated on the basis of the Hartree-Fock, coupled cluster with singles and doubles and of the double hybrid density functional calculations. A reliable value of the calibration constant (alpha(Fe-57) = -0.306 +/- 0.009 mm s(-1)) was obtained with the use of the B2-PLYP double hybrid density functional. This value is in good agreement with the experimentally estimated constant of -0.31 +/- 0.04 a(0)(3) mm s(-1) and can be recommended for theoretical modeling of Fe-57 isomer shifts.

We report on the evolution of the P L2,3 VV Auger line shape with increasing Yb deposition onto the GaP(110) surface. Strong affinity with Si L2,3 VV profiles measured from the Si(111)/Yb interface and nearly-d0 metal silicides (Ca silicides, Gd silicides) is pointed out and fruitfully exploited to model the character of the P 3p-derived valence states in the Yb phosphidelike reaction products. The chemical bond is thus ascribed mainly to the formation of P 3p - Yb 5d hybrids.

A study of the formation of In- and Au-GaAs(100) interfaces is reported. The metal overlayers are deposited in ultrahigh vacuum on room-temperature (RT) and low-temperature (LT) (100)GaAs grown by molecular-beam epitaxy, following the evaporation of a protective As capping layer from the semiconductor surface. High-resolution photoemission spectroscopy and low-energy electron diffraction are used to characterize these interfaces. In forms a two-dimensional interface layer plus clusters at RT and LT, with reduced clustering at LT. The top substrate layers are only slightly altered by In. The Au-induced perturbation is more significant, as reflected by Ga outdiffusion even at LT. Different Ga core-level components are found at RT and LT, attesting to different levels of segregation as a function of temperature. The GaAs(100) band bending is studied as a function of metal coverage and deposition temperature. Kelvin-probe measurements, coupled with synchrotron-radiation photoemission, are performed to evaluate the synchrotron-light-induced surface photovoltage. The Fermi level is found to be pinned at 0.4 and 0.6 eV above the valence-band maximum for Au and In, respectively, in good agreement with the positions obtained on the cleaved (110) GaAs surface. Evidence of correlation between pinning and overlayer metallization is found for both interfaces.

We report a P L2, 3 VV Auger line-shape study of the early stages of the GaP(110)/Yb interface formation. Strong similarities with the evolution displayed by the Si L2, 3 VV Auger profiles measured from the Si(111)/Yb interface and nearly-d0 metal silicides (Ca-silicides, Gd-silicides) is pointed out and exploited to determine the character of the P 3p-derived valence states in the Yb phosphide-like reaction products. A comparison, at different Yb coverages, with the self-folded partial density of states calculated for stoichiometric YbP is moreover performed. On this basis, the chemical bond is mainly described in terms of the formation of P 3p-Yb 5d hybrids.

Wet and dry oxide films-4H-SiC epitaxial (000 (1) over bar) C-face interfaces have been characterized by capacitance-voltage (C-V) measurements and soft x-ray excited photoemission spectroscopy (SX-PES) and hard x-ray excited photoemission spectroscopy (HX-PES) using synchrotron radiation. The interface state density for wet oxidation is much smaller than that for dry oxidation at any energy level. In the PES measurements, intermediate oxidation states such as Si1+ and Si3+ were observed. In addition, the areal densities of these states were found to be in a good correspondence with those of the interface states. The reasons for the good electrical characteristics of metal-oxide-semiconductor devices fabricated by wet oxidation are discussed in terms of the depth profiles of oxide films derived from the SX-PES and HX-PES results. (c) 2006 American Institute of Physics., copyright(c)2006 American Institute of Physics.