Publications

Fe doped ZnO particles of flower-like shape, hexagonal prisms and hybrid structures flower-prisms have been synthesized by hydrothermal technique, and their luminescence and magnetic properties have been investigated as a function of the morphology changes due to iron dopant (0-0.03 at.% Fe3+). The X-ray diffractograms of Zn1-xFexO powders indicated a hexagonal wurtzite polycrystalline structure. SEM images reveal the change of Zn1-xFexO grains shape from flower-like to hexagonal prisms as the Fe concentration (x) increases from 0 to 3 at.% Fe. Undoped ZnO shown weak room temperatures ferromagnetism, with high coercivity (H-c = 107 Oe) and saturation magnetization M-s of 1.5-10(-3) emu/g. ZnO doped with 1 and 3 at.% Fe presented a significant increase of the magnetization in comparison with the undoped ZnO. For ZnO doped with 3 at.% Fe, Ms = 32.5-10(-3) emu/g and M-rem = 0.78-10(-3) emu/g. Compared with other reports on magnetic properties of undoped and Fe doped ZnO, these results indicated higher coercivity and smaller magnetizations. The drop in the intensity of characteristic green-yellow photoluminescence band of ZnO at about 550-600 nm was attributed to the decrease of the number of oxygen vacancies and interstitial oxygen. By increasing the Fe concentration, the electron paramagnetic resonance (EPR) signal of undoped ZnO decreases due to the decrease of defects concentration. (C) 2017 Elsevier Ltd. All rights reserved.

In this paper, we investigate the influence of Cu, Co, and Al substitutions on the transport properties, and in particular, the magnetoresistive effect in Ni-Fe-Ga ferromagnetic shape memory alloys (FSMAs) prepared as ribbons by melt spinning method and subjected to different thermal treatments. X-ray diffraction, differential scanning calorimetry, magnetometry, and magnetoresistive characterizations were performed. In the range of the martensitic transformation (MT), different FSMA compositions show a rich spectrum of different behaviors. For one of the compositions (Ni52Fe20Co2Ga23Al3), the magnetoresistance (MR) showed a local minimum or, on the contrary, a local maxima of reduced amplitude on cooling, in the range of the MT, depending on the performed thermal treatments. In the same composition, by replacing one Al atom with a Co one, no local extremes are seen, the alloy having a concomitant magneto-structural transition. When the magnetic field was varied, the MR showed a nonmonotonic variation in the martensite phase for some compounds, possibly due to the dynamics of the martensite variants realignment. From the studied compositions, the highest MR found on the MT of -9% for 5 T is for Ni50Fe20Ga27Cu3.

A new facile template method for the preparation of Ni, Co doped ZrO2 self-assembled electrocatalysts for oxygen reduction reaction was employed. The effect of the Ni and Co incorporation into ZrO2 lattice on the structural, texturaL surface chemistry and its activity on ORR was emphasized. As X-ray diffraction reveals, the pseudo-cubic lattice of the tetragonal ZrO2 polymorph (t-ZrO2) is stabilized when Ni and Co are co-doping ZrO2. The results indicate that the synergetic effects arisen from the intimate electronic interaction of the mixed oxides present in the lattice of the zirconia phase, i.e. Nil-xCoxO (or NiO and CoO) in NCZ enhance the electrocatalytic activity of the catalyst. (C) 2017 Elsevier B.V. All rights reserved.

We investigated the evolution of the DC magnetic hysteresis curves of Nb0.89Ti0.11 alloys thermo-mechanically processed by intermediate heat treatments at 900 degrees C in vacuum and cold rolling (similar to 50% thickness reduction). Starting with a rectangular piece (similar to 0.4 mm thick) cut from the as-grown alloy, after the first thermo-mechanical treatment, the specimen exhibits over a wide temperature T interval a peak effect not far from the DC irreversibility line. With a supplemental thermo-mechanical treatment, the peak effect disappears and is substituted by a second magnetization peak ( where the characteristic fields are significantly lower) induced by pinning enhancement. The second magnetization peak was clearly seen at high temperatures only, due to the occurrence of thermo-magnetic instabilities in the low-T domain. In both cases, analysis of magnetic relaxation evidences a crossover towards plastic vortex creep accompanying the maximum in the effective critical current density. These results suggest a common nature of the observed effects, related to the disordering of the vortex system induced by pinning.

In this paper the influence of the heat treatment on the structural and optical properties of oxide single layer and multilayer transparent thin film structures of ITO/Au/ITO, AZO/Au/AZO, TiO2/Au/TiO2 and Bi2O3/Au/Bi2O3 type is studied. The single-layer oxides and respective multilayer structures have been deposited on glass substrates by successive DC magnetron sputtering using metallic targets ln:Sn, Zn:Al, Ti and Bi, in reactive (for the oxide films) or inert (for the metallic Au interlayer films) atmosphere. Good quality transparent conducting thin film structures have been obtained, with resistivity similar to 10(-4) Omega cm and transmittance similar to 75%. The wetting surface properties in function of time exposure at UV radiation (254 nm) have been also studied before and after heat treatment performed at 450 degrees C. (C) 2017 Elsevier Ltd. All rights reserved.

The electronic structure of the SiO2/SiC (0001) interface, buried below SiO2 layers with a thickness from 2 to 4 nm, was explored using soft X-ray angle-resolved photoemission spectroscopy with photon energies between 350 and 1000 eV. The measurements have detected the characteristic k-dispersive energy bands of bulk Silicon Carbide (SiC) below the SiO2 layer without any sign of additional dispersive states, up to an estimated instrumental sensitivity of approximate to 5 x 10(9) cm 2 eV. This experimental result supports the physical picture that the large density of interface traps observed in macroscopic measurements results from dangling bonds randomized by the SiO2 rather than from Shockley-Tamm surface derived states extending into the bulk SiC. Published by AIP Publishing.

Amorphous hematite synthesized by a simple and fast microwave route was used to obtain Fe16N2 fine particles by reducing in 5% H-2/Ar gas flow, followed by long time nitridation in ammonia gas flow at temperatures below 200 degrees C. Depending on nitridation temperature, various amounts of metallic iron were present along with the alpha" -Fe16N2 main phase. A small amount of iron oxide was observed by Mossbauer spectroscopy, but it was undetected by X-ray diffraction due to its high degree of amorphization. Increased amounts of Fe3N and Fe4N phases were observed at a nitridation temperature above 150 degrees C, which had a detrimental effect on the magnetic properties. Structural information and phase composition were extracted from Rietveld refinement of the XRD data. Values of the magnetization at saturation measured at 40 kOe and 25 degrees C of 222 emu/g for alpha"-Fe16N2 and 192 emu/g for metallic iron were obtained via magnetic measurements, Rietveld, and Mossbauer analysis.

We present a comparative study between the properties of Yb3+/Er3+ co-doped LiYF4 thin films obtained by pulsed laser deposition (PLD) and matrix-assisted pulsed evaporation (MAPLE) growth techniques, respectively. We performed structural, morphological, and optical analyses in order to draw a conclusion about the potential of MAPLE as a growth technique used for the obtaining of RE-doped fluoride thin films having up-conversion properties. For both techniques the surface morphology is typical for laser processed thin films of RE-doped fluorides, with roughness values of the order of few hundreds of nanometers and a higher density of defects in the sample obtained by MAPLE. Up-conversion properties do not exhibit major differences between the thin film samples and the pressed target. Under 980 nm laser light pumping, both Yb3+/Er3+ co-doped LiYF4 thin film samples, obtained by PLD and MAPLE, show green ((H-2(11/2), S-4(3/2)) -> I-4(15/2)) and red (F-4(9/2) -> I-4(15/2)) up-conversion luminescence explained by a two-photon processes. Therefore MAPLE is a viable growth technique for the fundamental study of RE-doped fluoride thin films and their respective functional properties. (C) 2017 Elsevier B.V. All rights reserved.

We report the structural, electronic and magnetic investigation using extended X-ray absorption fine structure spectroscopy (EXAFS), photoelectron microscopy, spin-resolved photoemission and magneto-optical Kerr effect on the properties of MnGe systems obtained by molecular beam epitaxy deposition of manganese on Ge(001) wafers annealed on temperatures between 50 and 450 C. Magnetic ordering can be achieved when the substrate temperature is higher than 250 C, when the manganese tends to diffuse into the Ge matrix and segregate in MnGe-like compounds, as proved by EXAFS. High spatial resolution photoelectron spectroscopy reveals Mn inhomogeneities in the 5-10 m range, even though Mn is found mostly in the same chemical state all over the surface.

The present work was focused on the synthesis and characterization of hydroxyapatite doped with low concentrations of zinc (Zn: HAp) (0.01 < x(Zn) < 0.05). The incorporation of low concentrations of Zn2+ ions in the hydroxyapatite (HAp) structure was achieved by co-precipitation method. The physico-chemical properties of the samples were characterized by X-ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), zeta-potential, and DLS and N2-BET measurements. The results obtained by XRD and FTIR studies demonstrated that doping hydroxyapatite with low concentrations of zinc leads to the formation of a hexagonal structure with lattice parameters characteristic to hydroxyapatite. The XRD studies have also shown that the crystallite size and lattice parameters of the unit cell depend on the substitutions of Ca2+ with Zn2+ in the apatitic structure. Moreover, the FTIR analysis revealed that the water content increases with the increase of zinc concentration. Furthermore, the Energy Dispersive X-ray Analysis (EDAX) and XPS analyses showed that the elements Ca, P, O, and Zn were found in all the Zn: HAp samples suggesting that the synthesized materials were zinc doped hydroxyapatite, Ca10-Zn-x(x)(PO4) (6)(OH), with 0.01 <= x(Zn) <= 0.05. Antimicrobial assays on Staphylococcus aureus and Escherichia coli bacterial strains and HepG2 cell viability assay were carried out.