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Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases., This work was supported by the French National Research Agency through contract ORGANI'SO (ANR-15-CE09-0017). A. C. G. H. and J. C. thank Laurence Magaud for fruitful discussion about the simulation of the structure of the molecules. F. C. thanks Sarah Benchabane for fruitful discussion. C. S. S., J. I. M. and J. A. M. G. acknowledge financial support from Spanish MINECO (MAT2017-85089-C2-1-R, RYC-2015-17730, RYC-2018-024364-I), European Research Council (ERC) under contract (ERC-2013-SYG-610256 NANOCOSMOS), Comunidad de Madrid via Programa de Investigación Tecnologías 2018 (FOTOART-CM S2018/NMT-4367), and the innovation program under grant agreements 785219 and 881603 (GrapheneCore2 and GrapheneCore3-Graphene-based disruptive technologies, respectively). E. M. acknowledges financial support from Région Rhône Alpes (ARC6 program) and the Labex LANEF. J. C. and J. A. M. G. acknowledges financial support from CNRS and CSIC via the IEA program (PIC2017-FR4/07981), under the ORGAN'X project.

International audience; The surface structure of Mg-doped rutile TiO 2 (011) surfaces is determined by combining core level/valence band photoemission and photoelectron diffraction (PED) to evolutionary algorithm, density functional theory (DFT) and multiple scattering calculations. Upon annealing the reduced crystal above 620 K, Mg segregates by substitution to Ti atoms from the TiO 2 lattice while keeping the known reconstruction of the Mg-free surface. Band gap states being totally healed by Mg segregation, the charge compensation is provided by O vacancies as formally expressed by the Kröger and Vink notation. A full support to those findings comes from

The surface structure of Mg-doped rutile TiO2 (011) surfaces is determined by combining the core-level or valence band photoemission and photoelectron diffraction (PED) measurements with evolutionary algorithm, density functional theory (DFT), and multiple scattering calculations. Upon annealing the reduced crystal above 620 K, Mg segregates by substitution to the Ti atoms from the TiO2 lattice while retaining the known reconstruction of the Mg-free surface. Since the band gap states are totally healed by the Mg segregation, the charge compensation is provided by the O vacancies as formally expressed by the Kr?ger and Vink notation. Full support of these findings comes from DFT calculations based on the findings from evolutionary algorithm calculations, which demonstrate that a combination of four surface structures nicely accounts for the observed experimental Ti 3s and Mg 2s patterns. These model structures only involve Mg in the substitutional position and O vacancies, and neither interstitial atoms nor excess electrons were experimentally detected.

Hybrid semiconductor/superconductor devices constitute an important platform for a wide range of applications, from quantum computing to topological-state-based architectures. Here, we demonstrate full modulation of the interference pattern in a superconducting interference device with two parallel islands of ballistic InAs quantum wells separated by a trench, by acting independently on two side gates. This so far unexplored geometry enables us to tune the device with high precision from a SQUID-like to a Fraunhofer-type behavior simply by electrostatic gating, without the need for an additional in-plane magnetic field. These measurements are successfully analyzed within a theoretical model of an extended tunnel Josephson junction, taking into account the focusing factor of the setup. The impact of these results on the design of novel devices is discussed. Hybrid semiconductor/superconductor devices constitute an important platform for a wide range of applications, from quantum computing to topological-state-based architectures. Here, we demonstrate full modulation of the interference pattern in a superconducting interference device with two parallel islands of ballistic InAs quantum wells separated by a trench, by acting independently on two side gates. This so far unexplored geometry enables us to tune the device with high precision from a SQUID-like to a Fraunhofer-type behavior simply by electrostatic gating, without the need for an additional in-plane magnetic field. These measurements are successfully analyzed within a theoretical model of an extended tunnel Josephson junction, taking into account the focusing factor of the setup. The impact of these results on the design of novel devices is discussed.

International audience; Phase controlled multilayer mirrors provide an efficient solution to transport, focus and/or compress attosecond pulses in the extreme ultraviolet (EUV) domain (30 – 100 eV). In this spectral range, one can access the spectral phase of the multilayer stack by measuring the photocurrent generated at the mirror surface as a function of the incoming photon energy. It has been already demonstrated that one can extract the spectral phase from such measurements under specific hypotheses. In this paper, we present the experimental protocol for such measurements and discuss the validity of this technique in the EUV and in the soft x-ray domains. In the EUV spectral range, our experimental results are in good agreement with simulations. However, the previous hypotheses are no longer valid at shorter wavelengths, in the soft xrays domain. This is mainly due to the fact that the electron mean free path becomes comparable to the individual layer thickness in the multilayer mirror. Here we propose a new method that enables one to extend the validity of phase characterization using photocurrent measurements in the soft x-ray domain (100 – 1000 eV). We present the first experimental results concerning the phase characterization of Cr/Sc multilayer mirrors in the water window and compare these results with simulation.

Arsenic contamination of floodplain soils is extensive and additional fresh arsenic inputs to the pedosphere from human activities are ongoing. We investigate the cumulative effects of repetitive soil redox cycles, which occur naturally during flooding and draining, on a calcareous fluvisol, the native microbial community and arsenic mobility following a simulated contamination event. We show through bioreactor experiments, spectroscopic techniques and modelling that repetitive redox cycling can decrease arsenic mobility during reducing conditions by up to 45%. Phylogenetic and functional analyses of the microbial community indicate that iron cycling is a key driver of observed changes to solution chemistry. We discuss probable mechanisms responsible for the arsenic immobilisation observed in-situ. The proposed mechanisms include, decreased heterotrophic iron reduction due to the depletion of labile particulate organic matter (POM), increases to the proportion of co-precipitated vs. aqueous or sorbed arsenic with α-FeOOH/Fe(OH) 3 and potential precipitation of amorphous ferric arsenate.

We have performed a layer-resolved, microscopic study of interactions between domain walls in two magnetic layers separated by a non-magnetic one, using high-resolution x-ray photoemission electron microscopy. Domain walls in the hard magnetic Co layer of a Co/Al2O3/FeNi trilayer with in-plane uniaxial anisotropy strongly modify the local magnetization direction in the soft magnetic FeNi layer. The stray fields associated to the domain walls lead to an antiparallel coupling between the local Co and FeNi moments. For domain walls parallel to the easy magnetization axis this interaction is limited to the domain wall region itself. For strongly charged (head-on or tail-to-tail) walls, the antiparallel coupling dominates the interaction over radial distances up to several micrometers from the centre of the domain wall., Comment: Published version, J. Phys.: Condens. Matter 19, 476204 (2007)

The authors report on a method to tune the orientation of in-plane magnetic domains and domain walls in thin ferromagnetic strips by manipulating the magnetic anisotropy of the system. Uniaxial in-plane anisotropy is induced in a controlled way by oblique evaporation of magnetic thin strips. A direct correlation between the magnetization direction and the domain wall orientation is found experimentally and confirmed by micromagnetic simulations. The domain walls in the strips are always oriented along the oblique evaporation-induced easy axis, irrespective of the shape anisotropy. The controlled manipulation of domain wall orientations could provide promising possibilities for recently proposed devices based on domain wall propagation.

The aim of this work is to give an exhaustive characterization ofthe local structure for two class of compounds: sodium dopedlanthanum manganites and tungsten doped iron-molybdenumdouble-perovskites. Both class of materials usually behave asconductors in the ferromagnetic phase and undergo ametal-to-insulator transition, associated with aferromagnetic-to-paramagnetic(antiferromagnetic) transition, uponvarying the temperature or the doping level. It is widely acceptedthat in manganites, as well as in double-perovskites, transportproperties are strongly influenced by the local structure (bondlengths and angles) around key sites, occupied by magnetic ions. Forthis reason the X-ray absorption spectroscopy (XAS), being sensitiveto the local order around the absorber atom, is the more suitabletechnique to study such compounds. In this work, the local structureof Na-doped manganites in the form of thin films has been studied asa function of the film thickness, while, bulk samples of tungstendoped iron-molybdenum double perovskite series have beeninvestigated to characterize the local structure as a function ofthe doping level and to better understand the nature of themetal-to-insulator transition. It was necessary to develop a TEYdetector. which realization was challenging from a technical pointof view and it required an extensive theoretical and technical work.X-ray absorption measurements were done at the Italian beam line fordiffraction and absorption (GILDA-BM08) at the European SynchrotronRadiation Facility (ESRF) of Grenoble (France).; L'objectif de cet étude est de donner une caractérisation complètede la structure locale de deux classes de composés : les manganitesde lanthane droguées avec du sodium et les doubles perovskites deferro-molybdène droguées avec du tungstène. Les deux classes secomportent, en général comme de conducteurs dans leur phaseferromagnétique et, suivant variations de température ou de dopage,ils subissent une transition métal-isolant à laquelle il fautassocier une transitionferromagnétique-paramagnétique(antiferromagnétique). En effet, ilest tout à fait accepté que aussi bien dans les manganites, que dansles perovskites doubles, les propriétés de transport sontinfluencées d'une façon importante par la structure locale (longueuret angle de liaison) autour des sites clés occupés par des ionsmagnétiques. Pour cette raison la spectroscopie d'absorption derayon X, en étant sensible à l'ordre locale autour de l'atomeabsorbeur, constitue la technique la plus adaptée pour l'étude deces composés. La structure locale de film fins de manganite droguéesavec du sodium a été étudiée en fonction de l'épaisseur des film.Des échantillons de poudre de perovskites double droguées avectungstène ont été étudiées pour en caractériser la structure localeen fonction du dopage et pour chercher de comprendre la nature de latransition métal-isolant. Il a été nécessaire de développer undétecteur d'électrons. La réalisation de cet instrument s'est révéléun défi du point de vue technique et il a demandé une quantité detravail aussi bien sur la plan pratique que théorique. Les mesuresd'absorption de rayon-X ont été effectuées à la ligne de lumièreitalienne pour la diffraction et l'absorption (GILDA-BM8) àl'Installation Européenne de Rayonnement de Synchrotron (ESRF) deGrenoble (France).