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Publications (89)
Implementing a newly developed spectrometer for the soft x‐ray range of (35–130) eV based on reflection zone plates was successfully accomplished on an electron probe microanalyzer. In this context, we present the first spectra acquired using this setup, including those of elements such as Be (Kα), C (Kα), Mg (L 2,3 ), Al (L 2,3 ), and Si (L 2,3 )....
Hard x‐ray emission spectroscopy (XES) has been used to study buried layers and interfaces in a Fe/Si periodic multilayer. Until now, buried layers could be studied using the XES in the soft x‐ray range. Here, we extend the methodology to study the buried interfaces in hard x‐ray region (photon energy ≥ 5 keV). We report the formation of FeSi2 at a...
Lattice dynamics of low-dimensional BaVS3 is reported across the metal-insulator Peierls transition occurring at TP=69 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density-functional theory calculations. The nondetection of a Kohn anomaly points to a unique situation of an order-disorder Peierls...
Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids,-(BEDT-TTF) 2 Ag 2 (CN) 3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the u...
Here, the first accurate study is presented of the room-temperature and 100 K structures of one of the first organic spin liquids, κ-(BEDT-TTF)2Ag2(CN)3. It is shown that the monoclinic structure determined previously is only the average one. It is shown that the exact structure presents triclinic symmetry with two non-equivalent dimers in the unit...
The lattice dynamics of low-dimensional BaVS 3 is reported across the hexagonal-orthorhombic phase transition occurring at TS = 250 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density functional theory calculations. We observed the occurrence of strongly temperature-dependent diffuse scattering...
The lattice dynamics of low-dimensional BaVS 3 is reported across the hexagonal-orthorhombic phase transition occurring at T S = 250 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density functional theory calculations. We observed the occurrence of strongly temperature-dependent diffuse scatterin...
Iridates are often viewed as an equivalent of cuprates with strong spin-orbit coupling. As such, they offer a new way to study the physics of Mott insulators. The hybridization with oxygen is, of course, essential in both compounds and may play a crucial role in the doping process. It could be quite different in the two families, iridates being 5d...
The Kossel effect is the diffraction by a periodically structured medium, of the characteristic X-ray radiation emitted by the atoms of the medium. We show that multilayers designed for X-ray optics applications are convenient periodic systems to use in order to produce the Kossel effect, modulating the intensity emitted by the sample in a narrow a...
The lattice dynamics of low-dimensional BaVS 3 is reported across the hexagonal-orthorhombic phase transition occurring at T S = 250 K using a combination of the thermal diffuse scattering of x rays, inelastic x-ray scattering, and density functional theory calculations. We observed the occurrence of strongly temperature-dependent diffuse scatterin...
Pd/Y multilayers are high reflectance mirrors designed to work in the 7.5-11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B4C barrier layers located at the interfaces of Pd and Y layers to reduce interdiffusion, which is expected by calculating mixing enthalpy of Pd and Y. Grazing incident x-ray refl...
Pd/Y multilayers are high-reflectance mirrors designed to work in the 7.5–11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B4C barrier layers located at the interfaces of the Pd and Y layers to reduce interdiffusion, which is expected from calculating the mixing enthalpy of Pd and Y. Grazing-incident...
We present here the first accurate determination of the exact structure of κ-(BEDT-TTF)2Cu2(CN)3. Not only did we show that the room temperature structure used over the last twenty years was incorrect, but we were also able to correctly and precisely determine it. The results of our work provide evidence that the structure presents a triclinic symm...
Resonant inelastic x-ray scattering at the N K edge reveals clearly resolved harmonics of the anion plane vibrations in the κ-(BEDT-TTF) 2 Cu 2 (CN) 3 spin-liquid insulator. Tuning the incoming light energy at the K edge of two distinct N sites permits us to excite different sets of phonon modes. The cyanide (CN) stretching mode is selected at the...
Resonant inelastic x-ray scattering at the N K edge reveals clearly resolved harmonics of the anion plane vibrations in the kappa-(BEDT-TTF)2Cu2(CN)3 spin-liquid insulator. Tuning the incoming light energy at the K edge of two distinct N sites permits to excite different sets of phonon modes. Cyanide CN stretching mode is selected at the edge of th...
The Kossel interferences generated by characteristic x-ray lines produced inside a periodic multilayer have been observed upon proton irradiation, by submitting a Cr/B4C/Sc multilayer stack to 2 MeV protons and observing the intensity of the Sc and Cr K$\alpha$ characteristic emissions as a function of the detection angle. When this angle is close...
The Kossel interferences generated by characteristic X-ray lines produced inside a periodic multilayer have been observed upon proton irradiation, by submitting a Cr/B4C/Sc multilayer stack to 2 MeV protons and observing the intensity of the Sc and Cr Kα characteristic emissions as a function of the detection angle. When this angle is close to the...
We show that the quasi-1D behavior of BaVS3 can be understood analyzing the X-ray absorption near edge spectra at the sulfur K edge. Linear dichroism experiments, analyzed with the help of ab initio calculations, reveal two strong and polarization dependent pre-edge features, induced by the band character of the 3d vanadium levels. They are related...
V L3 edge resonant inelastic x-ray scattering measurements performed on high quality BaVS3 single crystals reveal that the intra-t2g dd excitations close to the elastic peak are suppressed below the metal-insulator transition induced by the Peierls instability. The depletion of electronic states close to the Fermi level represents a direct observat...
V L 3 edge resonant inelastic x-ray scattering measurements performed on high quality BaVS 3 single crystals reveal that the intra-t 2g dd excitations close to the elastic peak are suppressed below the metal–insulator transition induced by the Peierls instability. The depletion of electronic states close to the Fermi level represents a direct obser...
Besides two strong π⊥1* and π∥* resonances in the 398- to 400-eV energy range, N 1s near edge x-ray absorption fine structure spectra of acrylonitrile molecules have a less intense 401- to 403-eV doublet. The two components correspond to the N 1s → π⊥2* and N 1s → D∥* transitions, where D∥* is a diffuse state with strong Rydberg character. The vibr...
In this paper we review the salient features of the different instabilities exhibited by the quasi-1D system BaVS3 and show that there is a subtle interplay between the different phases stabilized. The analysis of the Peierls instability shows that the mobile dz² electrons are more localized than calculated because of their strong correlation with...
The hole distribution in Sr14Cu24O41 is studied by low-temperature polarization-dependent O K near-edge x-ray absorption fine-structure measurements and state-of-the-art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semiempirical models, we show...
Polarization dependent vanadium L edge X-ray absorption spectra of BaVS$_3$
single crystals are measured in the four phases of the compound. The difference
between signals with the polarization \textbf{E}$\perp$\textbf{c} and
\textbf{E}$\parallel$\textbf{c} (linear dichroism) changes with temperature.
Besides increasing intensity of one of the maxi...
Polarization dependent vanadium L edge x-ray absorption spectra of BaVS 3 single crystals are measured in the four phases of the compound. The difference between signals with the polarizations E ? c and E k c (linear dichroism) changes with temperature. Besides increasing the intensity of one of the maxima, a new structure appears in the pre-edge r...
Polarization dependent vanadium L edge X-ray absorption spectra of BaVS3 single crystals are measured in the four phases of the compound. The difference between signals with the polarization E⊥c and Ec (linear dichroism) changes with temperature. Besides increasing intensity of one of the maxima, a new structure appears in the pre-edge region below...
The hole distribution in Sr$_{14}$Cu$_{24}$O$_{41}$ is studied by low temperature polarization dependent O K Near-Edge X-ray Absorption Fine Structure measurements and state of the art electronic structure calculations that include core-hole and correlation effects in a mean-field approach. Contrary to all previous analysis, based on semi-empirical...
This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal,...
Resonant magnetic x-ray scattering near the vanadium L2,3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below TN=31K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.2260.226xi) in hexagonal notation, with xi=0.033. The azimut...
Resonant magnetic x-ray scattering near the vanadium L-2,L-3-absorption edges has been used to investigate the low temperature magnetic structure of high quality BaVS3 single crystals. Below T-N = 31 K, the strong resonance revealed a triple-incommensurate magnetic ordering at the wave vector (0.226 0.226 xi) in hexagonal notation, with xi = 0.033....
We investigate magnetic excitations in the spin-ladder compound Sr_{14}Cu_{24}O_{41} using high-resolution Cu L_{3} edge resonant inelastic x-ray scattering (RIXS). Our findings demonstrate that RIXS couples to two-triplon collective excitations. In contrast to inelastic neutron scattering, the RIXS cross section changes only moderately over the en...
Using Resonant Inelastic X-ray Scattering (RIXS) at the Cu L3 and O K edge we studied the spin-ladder/spin-chain compound Sr14Cu24O41 [1,2]. We observe collective spin-excitations from the ladders, which we assign to two-Triplon modes [3]. At the Cu L3 resonance the dispersion of the modes was mapped out, obtaining excellent sensitivity over the fu...
Using resonant inelastic x-ray scattering (RIXS) at the Cu $L_{3}$ edge in Sr$_{14}$Cu$_{24}$O$_{41}$ we study the dispersion of collective spin excitations in the ladder system along the leg-direction. From calculations within an effective Hubbard model for a finite-size cluster and optical selection rules the observed modes are assigned to two-tr...
The N 1s near edge x-ray absorption fine structure spectra of acrylonitrile gas are accurately reproduced by a complete ab initio multidimensional vibrational analysis. The role of π∗-orbital localization and hybridization on vibrations accompanying core excitation is discussed. Transition to the π⊥∗(C=C−C≡N) delocalized orbital excites mostly stre...
This paper focuses on the use and value of XPS and NEXAFS spectroscopies to unveil the nature of the chemical bond of various bifunctional nitrile molecules adsorbed on Si(001) 2x1 at 300 K. The adsorption modes are also discussed in the light of recent theoretical publications devoted to optimized geometries and reaction paths of these molecules o...
The room temperature adsorption of acetonitrile (CH3-C N) on Si(111)-7x7 is examined by synchrotron radiation N 1s x-ray photoemission and x-ray absorption spectroscopies. The experimental spectroscopic data point to multiple adsorption geometries. Candidate structures are optimized using density functional theory (DFT), the surface being simulated...
We have studied the adsorption geometries of benzonitrile
(C6H5-CN) deposited on Si(001)-2×1
at 300 K, using synchrotron radiation x-ray photoemission spectroscopy
and x-ray absorption spectroscopy. The experimental data are interpreted
through density functional theory calculations of ground and excited
states. It is shown that the molecule chemi...
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 Si(001)-2×1 surfaces, taking into
consideration the...
The experimental N(1s) near-edge x-ray-absorption fine-structure spectrum of the benzonitrile molecule in the gas phase shows well separated double peaks with different vibrational profiles. Hybrid density-functional theory calculations reveal that such a separation is a result of the conjugation effect on the nitrogen 2p orbitals and the double sp...
We investigated the resonant Auger process near the V 2p3∕2 edge in vanadium metal. Attention is centered on the onset of Auger decays and their behavior below the 2p3∕2 resonance. The 2p3∕23d3d decay has a crossover from the Raman-Auger to the normal Auger regime at the 2p ionization threshold. Meanwhile, Auger decays with core holes in the final...
We have extended the transition-state theory to describe the dynamics of core hole excitation. This allows us to interpret the abnormally bland near-edge x-ray absorption fine structure spectrum of the gas phase benzonitrile molecule at the N 1s edge. We have brought to light different paths for the two most intensive resonances, going from the lin...
The cycloaddition of acrylonitrile on the Si surface was discussed using density functional approach. It was found that the buckling of the surface dimers characteristic for the (2×1) reconstructed surface favored structures with a dipolar moment such as the resonant form of acrylonitrile with cumulative double bonds. It was observed that the absor...
We report results obtained by resonant photoemission (RPE) and X-ray magnetic circular dichroism (XMCD) in absorption with photon energies around the L2/3 edges of manganese. The samples contain manganese in different environments and details about the dynamics of electronic structure on one side, magnetic structure on the other side are being disc...
We have performed angle-resolved photoemission spectroscopy on InAs(0 0 1)4×2-c(8×2) clean surfaces in order to investigate two new electronic surface states related to the In-terminated InAs(0 0 1)4×2-c(8×2) clean surface. The experiments were carried out at normal emission as a function of photon energy using s- and p-polarized light. The surface...
We have studied Mn/InAs(001)(4×2)c(8×2) interfaces by high-resolution core-level spectroscopy, surface EXAFS and by X-ray magnetic circular dichroism (XMCD). The growth of manganese is found to depend strongly on the temperature of InAs. At low temperatures (room and liquid nitrogen temperature (LNT)), Mn atoms form the compound MnAs in the surface...
Interface reaction and magnetism of epitaxially-grown Fe on InAs(100) are studied by core-level photoemission (As 3d and In 4d) and Fe 2p X-ray magnetic circular dichroism using synchrotron radiation. The reactivity of Fe/InAs(100) is relatively low compared
to that of other interfaces involving deposition of 3d metals on III-V semiconductors. As a...
In contrast with the other interfaces involving deposition of 3d transition metals on III–V semiconductors (mostly GaAs), the Fe/InAs(1 0 0) interface exhibits magnetic properties even at the lowest coverage (1 monolayer, ML) investigated. The reactivity of the interface is also lower compared with Fe/GaAs. It involves formation of an interface com...
We have investigated clean In-terminated InAs(0 0 1)(4×2)-c(8×2) surface by LEED, STM and high-resolution core-level and valence band (VB) spectroscopies. The In4d and As3d core levels showed the presence of chemically shifted components. The decomposition of In4d core level exhibited a new surface component located close to that of free indium met...
We have applied the tool of resonant photoemission at the L3 absorption edge to thin Mn layers deposited on Cu(100). This allows us to study the transition from atomic to solid-state phase by following the 3d-band formation through the localization of a photon-excited electron in the presence of a 2p core hole. We have observed localized behavior f...
We have studied the growth of Fe thin layers on In-terminated InAs(100) surfaces by X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES) and reflection high energy electron diffraction (RHEED). Islanding is observed at the early stages of Fe deposition, then the growing mechanism is layer-by-layer. In thicker films, iron atoms...
The atoms of V exhibit a non-zero magnetic moment when alloyed with Fe or in ultrathin films deposited on Fe. In order to better understand this phenomenon which depends crucially on the atomic structure we have studied V/Fe(100) growth mode at different temperatures (300–800 K). RHEED intensity oscillations are observed during the V growth up to a...
Vanadium atoms present a magnetic moment different to zero when they are part of a thin film deposited on Fe or as a bimetallic Fe–V alloy. The understanding of this phenomenon can only be achieved with a correct structural description of these types of systems. We report an Auger electron diffraction investigation of V films grown on body cubic ce...
We present an x-ray diffuse scattering study of the anion ordering (AO)
transition in the
(TMTSF)2(ReO4)1-x(ClO4)x
solid solution of quasi-one-dimensional organic conductors and
superconductors. As (TMTSF)2ReO4 and
(TMTSF)2ClO4 present AO instabilities at different
critical wave vectors [q1=(12,12,12) and
q2=(0,12,0), respectively] this solid solut...
We present an x-ray diffuse scattering study of the one-dimensional substituted perylene radical-cation (M)2X-S salts, where M is the 1,2,7,8-tetrahydrodicyclopenta[cd,lm]-perylene or the 3,4,9,10-tetra-methylperylene radical cation, X the PF-6 or AsF-6 anion, and S a solvent molecule similar to CH2Cl2. These isostructural salts consist of stacks o...
We present a study of the organic alloys [(TMTSF)1−x(TMTTF)x]2ReO4. They exhibit an enhanced charge localization and a strong decrease of the () anion ordering (AO) transition temperature. Contrary to the (TMTDTSF)2ReO4 salt, this behavior does not interpolate that of the x=0 and x=1 pure compounds. It is ascribed to the presence of a 4kF site char...
We study an anisotropic nearest-neighbor Ising antiferromagnet on the triangular lattice, using Monte-Carlo simulations and random-phase (or related) approximations. Our main interest concerns the high-temperature magnetic scattering. Exact results are available at the disorder line (Stephenson; Welberry and Galbraith). Of greater experimental sign...
Seven Al–4.5 at% Zn–x at% Mg alloys, with x ranging between 0 and 3.0, are studied by X-ray powder diffraction. The following measurements are performed: (i) the dependence of the lattice constant of the α-phase of the as-quenched and the slowly cooled alloys on x at RT, (ii) the thermal expansion of the equilibrium η(MgZn2)-phase and its dissoluti...
Structural, electrical, and magnetic studies of [(TMTSF)[sub 1[minus][ital x]](TMTTF)[sub [ital x]]][sub 2]ReO[sub 4] alloys are reported. They exhibit around [ital x][similar to]0.5 an enhanced charge localization and a strong decrease of the (1/2,1/2,1/2) anion-ordering (AO) transition temperature. The localization enhancement is attributed to a...
We present an X-ray diffuse scattering study of the fluoranthene radical cation salt (FA)2PF6, where FA is the fluoranthene molecule, C16H10. Below room temperature this salt undergoes two successive structural phase transitions. The upper one, at T(C) almost-equal-to 200K, breaks the face center Bravais lattice symmetry. The lower one, of the Peie...
We present an X-ray diffuse scattering study of the fluoranthene radical cation salt (FA)2PF6, where FA is the fluoranthene molecule, C16H10. Below room temperature this salt undergoes two successive structural phase transitions. The upper one, at TC ≈200K, breaks the face center Bravais lattice symmetry. The lower one, of the Peierls type, corresp...
Substitutional and orientational disorders in some of the title compounds have been characterized by simulations of the X-ray diffuse scattering pattern. It is found that in most of the cases the disorder is random but accompanied by molecular displacements (size effect). The influence of a random disorder on the 2k(F) charge density wave (CDW), sp...
Pressure measurements on successively heat-treated YBa2Cu3O7-δ single crystals suggest that the out-of-plane resistivity (ρc) is diffusive even if dρc/dT is positive in high-quality samples. dρc/dT>0 comes from the temperature dependence of the in-plane lifetime of the particles which tunnel to the neighboring planes and dρc/dT<0 is due to phonon-a...
Completing a recent paper, the lattice constants of the Al-rich f.c.c. α-matrix (M) in equilibrium with (metastable) Guinier-Preston (GP) zones, a[α(M/GPZ)], as well as with the β(Zn)-equilibrium phase, a[α(M/β)], are followed during the decomposition (in most cases at RT) of ten Al-Zn alloys ranging in zinc content between x = 8 and 48 at%. The mo...
The formation of oxide phases in the system (1 -x) Fe2O3 +xGd2O3 was investigated for 0 ⩽x ⩽ 1. On the basis of XRD measurements the distribution of oxide phases, α-Fe2O3, Gd3Fe5O12, GdFeO3 and Gd2O3 was determined, as a function ofx. No solid solutions were observed with certainty even at the very ends of the concentration range. This was also con...
We report measurements of the in-plane (varrhoab) and out-of-plane resistivity (varrhoc) for YBa2Cu3O7-delta high temperature superconducting single crystals under hydrostatic pressure up to 20 kbar. varrhoab has an initial derivative d ln varrhoab/dP of -1.0% kbar, while for varrhoc, d ln varrhoc/dP is -1.5%/kbar at room temperature. The supercond...
We report measurements of the in-plane resistivity (ρab) and out-of-plane resistivity (ρc) on a Bi2Sr2CaCu2O8 high-temperature superconducting single crystal under hydrostatic pressure up to 20 kbar. ρab has an initial derivative d(lnρab)/dP of -0.75% kbar-1, while ρc depends much more strongly on pressure, d(lnρab)/dP≊-4.0% kbar-1. The superconduc...
We investigate magnetic excitations in the spin-ladder compound Sr$_{14}$Cu$_{24}$O$_{41}$ using high-resolution Cu $L_3$-edge Resonant Inelastic X-ray Scattering (RIXS). Our findings demonstrate that RIXS couples to collective spin excitations from a quantum spin-liquid ground state. In contrast to Inelastic Neutron Scattering (INS), the RIXS cros...
