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Abstract This work present structural, morphological, magnetic, and electrical properties of GaSb/Mn multilayer deposited via DC magnetron sputtering at room temperature and at 423 K. The samples are characterized by forming layers of 3, 6 and 12 periods of the GaSb/Mn structure. Through XRD patterns, it was possible to stablish the formation of GaSb, Mn3Ga, and Mn2Sb2 phases. FTIR measurements present an optical interference associated with periodicity and the homogenous thickness of the layers. HR-SEM shows the multilayer architecture with columnar microstructure in the formation of layers with grain nucleation on the surface. A ferromagnetic-like behavior was observed in the multilayers at room temperature related to the domains and interlayers interaction. Additionally, the hysteresis curves present shifts attributed to the effect of exchange bias coupling. I-V curves show RESET-SET states of the multilayer system with bipolar resistive behavior, which can be modified by external magnetic fields. The resistive switching evidenced corresponds to the conductive mechanism based on the capacitive conductance and the formation of conductive filaments in multilayer structure.

Abstract Ratchet devices allow turning an ac input signal into a dc output signal. A ratchet device is set by moving particles driven by zero averages forces on asymmetric potentials. Hybrid nanostructures combining artificially fabricated spin ice nanomagnet arrays with superconducting films have been identified as a good choice to develop ratchet nanodevices. In the current device, the asymmetric potentials are provided by charged Néel walls located in the vertices of spin ice magnetic honeycomb array, whereas the role of moving particles is played by superconducting vortices. We have experimentally obtained ratchet effect for different spin ice I configurations and for vortex lattice moving parallel or perpendicular to magnetic easy axes. Remarkably, the ratchet magnitudes are similar in all the experimental runs; i. e. different spin ice I configurations and in both relevant directions of the vortex lattice motion. We have simulated the interplay between vortex motion directions and a single asymmetric potential. It turns out vortices interact with uneven asymmetric potentials, since they move with trajectories crossing charged Néel walls with different orientations. Moreover, we have found out the asymmetric pair potentials which generate the local ratchet effect. In this rocking ratchet the particles (vortices) on the move are interacting each other (vortex lattice); therefore, the ratchet local effect turns into a global macroscopic effect. In summary, this ratchet device benefits from interacting particles moving in robust and topological protected type I spin ice landscapes.

Single-step synthesis and deposition of composite solid oxide fuel cell cathodes of composition (Nd,Gd)1/3Sr2/3CoO3−δ : Ce0.9(Gd,Nd)0.1O1.95 (70 : 30 w : w) with and without the addition of Ag nanoparticles (Ag NPs) was achieved employing spray pyrolysis and low-temperature sintering at 900 °C. Spray-pyrolysis-prepared materials offered improved microstructure with smaller particle size and higher porosity (extended triple phase boundary) in comparison to slurry-coated electrodes of analogous composition. Impedance spectroscopy of symmetrical cells of the composite air electrodes indicated a lower resistive response of the spray-pyrolysis-prepared electrodes with lower overall polarisation resistance (Rp), attributable to improved oxygen surface exchange and oxide-ion diffusion processes. Further reduction in Rp was achieved on decoration of the composite air electrodes with Ag NPs; the decorated composites were characterised by high resolution transmission electron microscopy (HRTEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Ag K-edge X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) of Ce0.9Gd0.1O2−δ:Ag spray-pyrolysed composites indicated that the Ag nanoparticles exhibit a core–shell structure with a Ag2O outer layer calculated to be two unit cells in thickness. The outer particle shell is suggested to participate in the enhanced electrochemical response, lowering the electrode polarisation response of symmetrical cells below 700 °C. Anode-supported single-cell fuel cells corresponding to the composite air electrode with Ag NPs and a thin YSZ-CGO electrolyte provided a maximum power density of 0.6 W cm−2 at 700 °C. [ABSTRACT FROM AUTHOR]

A controlled local enhancement of superconductivity yields unexpected modifications in the vortex dynamics. This local enhancement has been achieved by designing an array of superconducting Nb nanostructures embedded in a V superconducting film. The most remarkable findings are: (i) vanishing of the main commensurability effect between the vortex lattice and the array unit cell, (ii) hysteretic behavior in the vortex dynamics, (iii) broadening of the vortex liquid phase and (iv) strong softening of the vortex lattice. These effects can be controlled and they can be quenched by reducing the Nb array superconducting performance applying an in-plane magnetic field. These results can be explained by taking into account the repulsive potential landscape created by the superconducting Nb nanostructures on which vortices move.

Porous silicon (PSi) is a versatile matrix with tailorable surface reactivity, which allows the processing of a range of multifunctional films and particles. The biomedical applications of PSi often require a surface capping with organic functionalities. This work shows that visible light can be used to catalyze the assembly of organosilanes on the PSi, as demonstrated with two organosilanes: aminopropyl-triethoxy-silane and perfluorodecyl-triethoxy-silane. We studied the process related to PSi films (PSiFs), which were characterized by X-ray photoelectron spectroscopy (XPS), time of flight secondary ion mass spectroscopy (ToF-SIMS) and field emission scanning electron microscopy (FESEM) before and after a plasma patterning process. The analyses confirmed the surface oxidation and the anchorage of the organosilane backbone. We further highlighted the surface analytical potential of 13C, 19F and 29Si solid-state NMR (SS-NMR) as compared to Fourier transformed infrared spectroscopy (FTIR) in the characterization of functionalized PSi particles (PSiPs). The reduced invasiveness of the organosilanization regarding the PSiPs morphology was confirmed using transmission electron microscopy (TEM) and FESEM. Relevantly, the results obtained on PSiPs complemented those obtained on PSiFs. SS-NMR suggests a number of siloxane bonds between the organosilane and the PSiPs, which does not reach levels of maximum heterogeneous condensation, while ToF-SIMS suggested a certain degree of organosilane polymerization. Additionally, differences among the carbons in the organic (non-hydrolyzable) functionalizing groups are identified, especially in the case of the perfluorodecyl group. The spectroscopic characterization was used to propose a mechanism for the visible light activation of the organosilane assembly, which is based on the initial photoactivated oxidation of the PSi matrix.

Vicente Torres-Costa1, Gonzalo Martínez-Muñoz2, Vanessa Sánchez-Vaquero3, Álvaro Muñoz-Noval1, Laura González-Méndez3, Esther Punzón-Quijorna1,4, Darío Gallach-Pérez1, Miguel Manso-Silván1, Aurelio Climent-Font1,4, Josefa P García-Ruiz3, Raúl J Martín-Palma11Department of Applied Physics, 2Department of Computer Science, 3Department of Molecular Biology, 4Centre for Micro Analysis of Materials, Universidad Autónoma de Madrid, Madrid, SpainAbstract: The engineering of surface patterns is a powerful tool for analyzing cellular communication factors involved in the processes of adhesion, migration, and expansion, which can have a notable impact on therapeutic applications including tissue engineering. In this regard, the main objective of this research was to fabricate patterned and textured surfaces at micron- and nanoscale levels, respectively, with very different chemical and topographic characteristics to control cell–substrate interactions. For this task, one-dimensional (1-D) and two-dimensional (2-D) patterns combining silicon and nanostructured porous silicon were engineered by ion beam irradiation and subsequent electrochemical etch. The experimental results show that under the influence of chemical and morphological stimuli, human mesenchymal stem cells polarize and move directionally toward or away from the particular stimulus. Furthermore, a computational model was developed aiming at understanding cell behavior by reproducing the surface distribution and migration of human mesenchymal stem cells observed experimentally.Keywords: surface patterns, silicon, hMSCs, ion-beam patterning

Electrodeposition of gold into porous silicon was investigated. In the present study, porous silicon with ~100 nm in pore diameter, so-called medium-sized pores, was used as template electrode for gold electrodeposition. The growth behavior of gold deposits was studied by scanning electron microscope observation of the gold deposited porous silicon. Gold nanorod arrays with different rod lengths were prepared, and their surface-enhanced Raman scattering properties were investigated. We found that the absorption peak due to the surface plasmon resonance can be tuned by changing the length of the nanorods. The optimum length of the gold nanorods was ~600 nm for surface-enhanced Raman spectroscopy using a He-Ne laser. The reason why the optimum length of the gold nanorods was 600 nm was discussed by considering the relationship between the absorption peak of surface plasmon resonance and the wavelength of the incident laser for Raman scattering.

This work presents an experimental investigation which correlates the flexure load capacity loss of reinforced concrete beams with the amount of steel cross section loss due to localized corrosion of the embedded steel. Concrete beams (100x150x1500 mm) with the central portion contaminated by chlorides, placed during mixing of the concrete, were used in this investigation. By applying a 200 µA/cm2 constant anodic current for approximately 48 to 183 days, further acceleration of the corrosion process was achieved. After the corrosion-acceleration period was over, the specimens were tested in flexure under three-point loading. In addition, the average corrosion penetration, χAVER* estimated for each corroded beam from gravimetric metal loss. The results obtained show a decrease as high as 20% in the flexure load capacity values from the localized corroded specimens with only 14% of re bar radius loss.

Bimagnetic materials were fabricated by decorating the external surface of rattle-type hollow silica microspheres (which themselves contain metallic cobalt nanoparticles) with magnetite nanoparticles; thus, each magnetic substance was spatially isolated by the silica shell. The amount of magnetite decoration on the co-occluded hollow silica was varied from 1 to 17 mass %. Magnetic and electronic properties of the resulting bimagnetic materials were characterized by superconducting quantum interference device measurements and X-ray absorption spectroscopy, respectively. The ferrous iron in the bimagnetic sample was slightly more oxidized than in the magnetite reference, probably from some charge-transfer because of the SiO2 surface contact, although the overall oxidation state of the samples is very similar to that of magnetite. The temperature dependence of the sample magnetization recorded with Zero Field Cooling and Field Cooling resulted in blocking temperatures for the bimagnetic materials that were close to that of magnetite nanoparticles (176 K) and were lower than that for the bare Co-occluded hollow silica (which was above room temperature). Values of coercive force and exchange bias at 300 K became quite small after decoration with only minimal amounts of magnetite nanoparticles (1-3 mass %) and were lower than those of magnetite. This is the first example of enhancing superparamagnetism by spatial separation of both Co and magnetite magnetic nanoparticles using a thin wall of diamagnetic silica. [ABSTRACT FROM AUTHOR]

Materials with the formula Sr2CoNb1−xTixO6−δ (x=1.00, 0.70; δ=number of oxygen vacancies) present a cubic perovskite‐like structure. They are easily and reversibly reduced in N2 or Ar and re‐oxidized in air upon heating. Oxidation by water (wet N2), involving splitting of water at a temperature as low as 700 °C, produces hydrogen. Both compounds displayed outstanding H2 production in the first thermochemical cycle, the Sr2CoNb0.30Ti0.70O6−δ material retaining its outstanding performance upon cycling, whereas the hydrogen yield of the x=1 oxide showed a continuous decay. The retention of the materials' ability to promote water splitting correlated with their structural, chemical, and redox reversibility upon cycling. On reduction/oxidation, Co ions reversibly changed their oxidation state to compensate the release/recovery of oxygen in both compounds. However, in Sr2CoTiO6−δ, two phases with different oxygen contents segregated, whereas in Sr2CoNb0.30Ti0.70O6−δ this effect was not evident. Therefore, this latter material displayed a hydrogen production as high as 410 μmolH2  g−1perovskite after eight thermochemical cycles at 700 °C, which is among the highest ever reported, making this perovskite a promising candidate for thermosolar water splitting in real devices. [ABSTRACT FROM AUTHOR]

The in situ study of the discharge process in a zinc‐based half‐cell employing a porous electrode as a structural scaffold is reported. The in situ characterization has been performed by synchrotron X‐ray absorption fine‐structure spectroscopy and, for this purpose, an inexpensive, simple and versatile electrochemical cell compatible with X‐ray experiments has been designed and described. The experimental results reported here have been employed to semi‐quantify the dissolved and undissolved zinc species during the discharge, allowing the cell feasibility to be tested and to better understand the functioning of the zinc half‐cell based on porous electrodes. The in situ study of the discharge process in a zinc‐based half‐cell employing a porous electrode as a structural scaffold is reported. [ABSTRACT FROM AUTHOR]

The perovskite series Sr2CoNb1− xTi xO6− δ (0≤ x≤1) was investigated in the full compositional range to assess its potential as cathode material for solid oxide fuel cell (SOFC). The variation of transport properties and thus, the area specific resistances (ASR) are explained by a detailed investigation of the defect chemistry. Increasing the titanium content from x=0-1 produces both oxidation of Co3+ to Co4+ (from 0 up to 40 %) and oxygen vacancies (from 6.0 to 5.7 oxygen atom/formula unit), although each charge compensation mechanism predominates in different compositional ranges. Neutron diffraction reveals that samples with high Ti-contents lose a significant amount of oxygen upon heating above 600 K. Oxygen is partially recovered upon cooling as the oxygen release and uptake show noticeably different kinetics. The complex defect chemistry of these compounds, together with the compositional changes upon heating/cooling cycles and atmospheres, produce a complicated behavior of electrical conductivity. Cathodes containing Sr2CoTiO6− δ display low ASR values, 0,13 Ω cm2 at 973 K, comparable to those of the best compounds reported so far, being a very promising cathode material for SOFC. [ABSTRACT FROM AUTHOR]

This study examined the formation of amorphous platinum (Pt) clusters in nanopores of porous silicon at an initial stage of pore filling. The time dependency of the chemical state and local structure of Pt in the nanoporous silicon were characterized by X-ray absorption fine structure spectroscopy (XAFS). Initially, the Pt deposits showed non-negligible amounts of PtO 2 , formed by surface oxidation from the atmosphere, suggesting that the particle size was quite small. Deep analysis of extended XAFS (EXAFS) strongly suggested that Pt at the early stage of deposition was amorphous. The mechanism of amorphous Pt formation is discussed based on the confinement effect for Pt complex anions in nanopores. [ABSTRACT FROM AUTHOR]

La2−xCoTiO6−δ/Ce0.9Gd0.1O2−δ composites are presented as promising new cathodes for solid oxide fuel cells. The B-site ordering characteristic of double perovskites is present in the whole series. Additionally, increasing amounts of La-vacancies give rise to ordering of alternating La-rich and □-rich (□ = vacancy) layers perpendicular to the c-axis. The introduction of La vacancies produces both oxidation of Co2+ to Co3+ and oxygen vacancies inducing a change of both electrical and electrochemical properties. The best electrochemical performances are obtained for low x due to a compromise between sufficiently high amount of defects to provide electronic and ionic conductivities, but not so high to induce defect clustering. The material with x = 0.05 exhibits the best performances of the series. Symmetrical cells made of composites of this material and Ce0.9Gd0.1O2−δ deposited on pellets of this electrolyte show a polarization resistance of 0.39 Ω cm2 at 1073 K. [ABSTRACT FROM AUTHOR]

The evolution of the room-temperature structure of the oxide series La2− xSr xCoTiO6 (0.6 ≤ x ≤ 1.0) was studied as a function of the Sr content using different diffraction techniques and applying the symmetry-adapted modes formalism ( AMPLIMODES). The title compounds adopt perovskite-like structures of rhombohedral symmetry with an octahedral tilting scheme ( a−a−a−) with either space group or R32. The latter symmetry is observed in those cases (for x ≃ 0.6) where additional rock-salt-like ordering of La and Sr is produced in the perovskite A sites. Two composition-driven phase transitions are observed in the whole series La2− xSr xCoTiO6 (0.0 ≤ x ≤ 1.0). Using the concept of internal pressure, the effect of doping with Sr on the structure can be properly discussed. Both phase transitions seem to be of first order since they can be associated with discontinuities either in the entropy or in the structure. The first transition ( P21/ n → Pnma) occurs as the B cations become totally disordered. Along the whole compositional range the modes responsible for the out-of-phase tilting of BO6 octahedra remain active, but those associated with the in-phase octahedral tilting vanish for x ≥ 0.6, this being associated with the second transition ( Pnma → ). Finally, for x = 1.0 the three pseudo-cubic cell parameters become very similar, pointing to a transition to a cubic structure which could be obtained by applying pressure or raising the temperature. [ABSTRACT FROM AUTHOR]

The design of metallic hybrid systems for spintronics has been widely studied during the past decade, motivated by the promising technological applications of these materials. Nevertheless, the importance of preserving the native structure and properties of the interfaces is often ignored. Here, we present the fabrication of nanocrystalline Au (0 0 1) onto a single oriented Fe 3 O 4 (0 0 1) thin film as a promising hybrid system to develop spintronic devices by growing Au over the Fe 3 O 4 by using a simple one-pot Pulsed Laser Deposition (PLD) approach. The structural coupling between Au nanocrystals and Fe 3 O 4 layer results in the development of an incommensurate structure based on a coincidence lattice of order 35, which preserves the intrinsic properties of the Au nanocrystals, the Fe 3 O 4 matrix and the interface between them. The general strategy described in the present work preserves the structure and main intrinsic properties of the constituting materials, being a fundamental issue for the future development of spintronic devices. [ABSTRACT FROM AUTHOR]

A novel set-up has been designed and used for synchrotron radiation X-ray high-resolution powder diffraction (SR-HRPD) in transmission geometry (spinning capillary) for in situ solid-gas reactions and processes in an isobaric and isothermal environment. The pressure and temperature of the sample are controlled from 10−3 to 1000 mbar and from 80 to 1000 K, respectively. To test the capacities of this novel experimental set-up, structure deformation in the porous material zeolitic imidazole framework (ZIF-8) by gas adsorption at cryogenic temperature has been studied under isothermal and isobaric conditions. Direct structure deformations by the adsorption of Ar and N2 gases have been observed in situ, demonstrating that this set-up is perfectly suitable for direct structural analysis under in operando conditions. The presented results prove the feasibility of this novel experimental station for the characterization in real time of solid-gas reactions and other solid-gas processes by SR-HRPD. [ABSTRACT FROM AUTHOR]

Chemically sharp interface was obtained on single phase single oriented Fe3O4 (001) thin film (7 nm) grown on NiO (001) substrate using oxygen assisted molecular beam epitaxy. Refinement of the atomic structure, stoichiometry, and oxygen vacancies were determined by soft and hard x-ray photoelectron spectroscopy, low energy electron diffraction and synchrotron based X-ray reflectivity, and X-ray diffraction. Our results demonstrate an epitaxial growth of the magnetite layer, perfect iron stoichiometry, absence of oxygen vacancies, and the existence of an intermixing free interface. Consistent magnetic and electrical characterizations are also shown. [ABSTRACT FROM AUTHOR]