Determination of the magnetization profile of Co/Mg periodic multilayers by magneto-optic Kerr effect and X-ray magnetic resonant reflectivity

The resonant magnetic reflectivity of Co/Mg multilayers around the Co L2,3 absorption edge is simulated then measured on a specifically designed sample. The dichroic signal is obtained when making the difference between the two reflectivities measured with the magnetic field applied in two opposite directions parallel to the sample surface. The simulations show that the existence of magnetic dead layers at the interfaces between the Co and Mg layers leads to an important increase of the dichroic signal measured in the vicinity of the third Bragg peak that otherwise should be negligible. The measurements are in agreement with the model introducing 0.25 nm thick dead layers. This is attributed to the Co atoms in contact with the Mg layers and thus we conclude that the Co-Mg interfaces are abrupt from the magnetic point of view.Comment: 8 page

X-ray fluorescence induced by standing waves in the grazing-incidence and grazing-exit modes: study of the Mg--Co--Zr system

We present the characterization of Mg-Co-Zr tri-layer stacks by using x-ray fluorescence induced by x-ray standing waves, both in the grazing incidence (GI) and grazing exit (GE) modes. The introduction of a slit in the direction of the detector improves the angular resolution by a factor 2 and significantly the sensitivity of the technique for the chemical characterization of the buried interfaces. By observing the intensity variations of the Mg Kalpha and Co Lalpha characteristic emissions as a function of the incident (GI mode) or detection (GE mode) angle, we show that the interfaces of the Si/[Mg/Co/Zr] x30 multilayer are abrupt, whereas in the Si/[Mg/Zr/Co] x30 multilayer a strong intermixing occurs at the Co-on-Zr interfaces. The explanation of this opposite behaviour of the Co-on-Zr and Zr-on-Co interfacesis given by the calculation of the mixing enthalpies of the Co-Mg, Co-Zr and Mg-Zr systems, which shows that the Co-Zr system presents anegative value and the two others positive values. Together with the difference of the surface free energies of Zr and Co, this leads us to consider the Mg/Zr/Co system as aMg/Co x Zr y bi-layer stack, with x/y estimated around 3.5.Comment: Published in Journal of Synchrotron Radiation 22, 1419 (2015)http://scripts.iucr.org/cgi-bin/paper?S160057751501623

Structural and electronic properties of anisotropic ultrathin organic films from dichroic resonant soft x-ray reflectivity

We developed a quantitative approach for the determination of molecular arrangement and electronic structure in anisotropic organic ultrathin films based on the measurement of polarized reflectivity at the carbon K-edge. The reflectivity spectra were fitted to a parameterized model calculation. The method was applied to a self-assembled monolayer of 1,4-benzenedimethanethiol on gold. To simulate reflectivity, the organic anisotropic film was described by a dielectric tensor, obtained by ab initio calculations for the single molecule and suitable rotations to describe the molecular organization in film domains. Film structure was obtained though the best fit of the simulation to the experiment. Results were consistent with a monolayer-thick film composed of domains of molecules with in-plane isotropic distribution of orientations. In each domain, molecules adopted a standing configuration, with a tilt of 28° relative to the substrate normal. Information on the modification of the molecular electronic states due to chemical bonding was derived

SEI Growth and Depth Profiling on ZFO Electrodes by Soft X-Ray Absorption Spectroscopy

The evolution of the solid electrolyte interface (SEI) in carbon‐coated ZnFe2O4 (ZFO‐C) anodes is studied by soft X‐ray absorption spectroscopy (XAS). Experiments probe locally the SEI growth in the 2–100 nm range, using both total electron (TEY) and total fluorescence (TFY) yield techniques. XAS analysis shows that the SEI grows preferentially around the ZFO‐C nanoparticles

Oxygen impurities link bistability and magnetoresistance in organic spin valves

Vertical cross-bar devices based on manganite and cobalt injecting electrodes and metal-quinoline molecular transport layer are known to manifest both magnetoresistance and electrical bistability. The two effects are strongly interwoven, inspiring new device applications such as electrical control of the magnetoresistance and magnetic modulation of bistability. To investigate the full device functionality, we first identify the mechanism responsible for electrical switching by associating the electrical conductivity and the impedance behavior with chemical states of buried layers obtained by in operando photoelectron spectroscopy. These measurements revealed that a significant fraction of oxygen ions migrates under voltage polarity, resulting in a modification of the electronic properties of the organic material and of the oxidation of interfacial layer with ferromagnetic contacts. Variable oxygen doping of the organic molecule represents the key element for correlating bistability and magnetoresistance and our measurements provide the first experimental evidence in favor of the impurity band model describing the spin transport in organic semiconductors in similar devices

Visita all'Osservatorio della Biodiversità marina e terrestre della Regione Sicilia - ORBS

Con il taglio inaugurale del nastro il 16 dicembre 2015, prende vita la struttura museale permanente dell'Osservatorio della Biodiversità marina e terrestre della Regione Sicilia che porta lo stesso nome del Progetto di Ricerca "ORBS – Sistema di comunicazione, informazione e diffusione dell'Osservatorio Regionale della Sicilia", intitolata il 21 dicembre 2018 al Dott. Sandro Fiorelli. Ad oggi, la struttura, è operativa presso la Sede Secondaria dell'Istituto per lo studio degli impatti Antropici e Sostenibilità in ambiente marino del Consiglio Nazionale delle Ricerche (IAS – CNR) di Capo Granitola. Il progetto ORBS, finanziato da Regione Siciliana - Assessorato alla Cooperazione, Commercio, Artigianato e Pesca - Dipartimento Pesca, con periodo di attività 2013 - 2015, si è concluso proprio con la realizzazione della struttura museale; l'Osservatorio è stato istituito dall'Assessorato del Territorio e dell'Ambiente della Regione Siciliana nell'ambito di un accordo quadro con ARPA, ISPRA e CNR. Grazie al progetto ORBS, docenti e allievi dell'Accademia di Belle Arti di Palermo e il personale CNR – IAS (ex IAMC) S. S. di Capo Granitola, hanno collaborato sinergicamente permettendo di realizzare delle azioni didattiche e creative di valore scientifico espresse con straordinaria forza e bellezza. Ricercatori e professori si sono confrontati al fine di combinare le proprie competenze riuscendo nel progetto ambizioso di coinvolgere e fondere i diversi ambiti scientifici sensibilizzando gli artisti ai temi della Biodiversità. Le opere prodotte, corredate da schede scientifiche, hanno oltre al valore artistico un aggiunto valore didattico. L'apertura della sezione espositiva dedicata alla diffusione e alla comunicazione della biodiversità rappresenta da un lato l'importante tappa conclusiva del progetto, dall'altro l'inizio di un percorso mirato alla diffusione della biodiversità verso il mondo giovanile, le scuole e per tutto il territorio. Questa strepitosa collaborazione "CNR – Accademia di Belle Arti di Palermo" conferma l'importanza e l'opportunità di unire arte e scienza per esaltare la percezione della ricerca scientifica da parte della comunità. La divulgazione della scienza è un'attività complessa e sicuramente necessita di competenze e attitudini multidisciplinari oltreché di motivazione ed entusiasmo. La comunicazione delle tematiche scientifiche, di per sé ardua nella traduzione al grande pubblico, grazie alla forza esplicativa dell'arte, diviene opportunità di riflessione, osservazione, confronto per le comunità di visitatori. Il coordinamento delle visite delle scuole di ogni ordine e grado, Enti Pubblici, Comunità Scientifica, Cariche Istituzionali, Delegazioni di Politici Italiani e Stranieri, Associazioni Culturali, Associazioni No-Profit di Volontariato, Associazioni di Promozione Sociale, Organizzazioni di Volontariato, Onlus, pubblico in generale, presso ORBS, è affidato al qualificato personale (tecnici, tecnologi e ricercatori) dell'IAS – CNR S. S. di Capo Granitola, che gestisce in prima persona i visitatori nel percorso didattico e promuove il valore della divulgazione scientifica perseguendo la terza missione degli Enti di Ricerca, attraverso l'applicazione diretta, la valorizzazione e l'impiego della conoscenza

Optical constants of e-beam evaporated titanium dioxide thin films in the 25.5-to 612-eV energy region

The optical constants of titanium dioxide (TiO2) have been experimentally determined at energies in the extreme ultraviolet and soft x-ray spectral regions, from 25.5 to 612 eV. Measuring angle-dependent reflectance of amorphous TiO2 thin films with synchrotron radiation at the BEAR beamline of Synchrotron ELETTRA. The experimental reflectivity profiles were fitted to the Fresnel equations using a genetic algorithm applied to a least-square curve fitting method, obtaining values for \u3b4 and \u3b2. We compared our measurements with tabulated data. All samples were grown on Si (100) substrates by the electron-beam evaporation technique, with a substrate temperature of 150\ub0C and deposition rates of 0.3 to 0.5 \uc5 15s. Complete films characterization have been carried out with structural (XRD, ellipsometry, and profilometry), compositional (x-ray photoelectron spectroscopy), and morphological (atomic force microscopy) analyse

Relating structure with morphology: A comparative study of perfect Langmuir–Blodgett multilayers

Atomic force microscopy and X-ray reflectivity of metal-stearate (MSt) Langmuir-Blodgett films on hydrophilic Silicon (1 0 0), show dramatic reduction in 'pinhole' defects when metal M is changed from Cd to Co, along with excellent periodicity in multilayer, with hydrocarbon tails tilted 9.6° from vertical for CoSt (untilted for CdSt). Near edge X-ray absorption fine structure (NEXAFS) and Fourier transform infra-red (FTIR) spectroscopies indicate bidentate bridging metal-carboxylate coordination in CoSt (unidentate in CdSt), underscoring role of headgroup structure in determining morphology. FTIR studies also show increased packing density in CoSt, consistent with increased coverage