National Institute Of Materials Physics - Romania

For practical applications of superconducting materials in applied magnetic fields, artificial pinning centres in addition to natural ones are required to oppose the Lorentz force. These pinning centres are actually various types of defects in the superconductor matrix. The pinning centres can be categorised on their dimension (volume, surface or point) and on their character (normal cores or AK cores). Different samples have been produced by Pulsed Laser Deposition, with various thicknesses, temperatures and nanostructured additions to the superconducting matrix. They have been characterized by SQUID Magnetic Properties Measurement System and Physical Properties Measurement System, as well as by Transmission Electron Microscopy (TEM). Correlations between pinning architecture, TEM images, and critical currents at various fields and field orientations will be shown for a large number of YBa2Cu3Ox films with various types and architectures of artificial pinning centres. (C) 2016 Elsevier B.V. All rights reserved.

The specific magnetic structure and magnetic relaxation phenomena in magnetite nanoentities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr2O3 and P2O5, were investigated. The structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr2O3 generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P2O5 displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe3+ and Fe2+ ions; and the interplay between the relaxation mechanisms in different temperature ranges.

In this paper, the interaction of poly(vinylidene fluoride) (PVDF) with single-walled carbon nanotubes (SWNTs) highly separated in metallic (M) and semiconducting (S) tubes is studied by resonant Raman scattering and FTIR spectroscopy. In this order, the PVDF/SWNTs membranes were prepared by the evaporation of dimethylformamide (DMF) from PVDF solutions containing i) the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) tubes (M + S-SWNTs), ii) SWNTs highly separated in metallic tubes (98%, M-SWNTs), and iii) SWNTs highly separated in semiconducting tubes (99%, S-SWNTs). An increase in the PVDF beta phase weight, highlighted by the increase in the absorbance of IR band at 843 cm(-1), is reported to take place in the presence of M + S-SWNTs and S-SWNTs. An increase of the PVDF gamma crystalline phase weight is reported for the PVDF/M + S-SWNTs, PVDF/M-SWNTs and PVDF/S-SWNTs membranes. Using Raman scattering, a donor-acceptor interaction is invoked to take place at the interface PVDF/M + S-SWNTs and PVDF/S-SWNTs. In the case of the membranes based on PVDF and M-SWNTs, the changes reported in Raman spectra of the two constituents are explained on the base induction-interaction forces between the permanent dipole of PVDF and induced dipole of M-SWNTs. (C) 2016 Elsevier B.V. All rights reserved.

There is an ongoing debate regarding the mechanism of swift heavy ion (SHI) track formation in CaF2. The objective of this study is to shed light on this important topic using a range of complementary experimental techniques. Evidence of the threshold for ion track formation being below 3 keV nm(-1) is provided by both transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy in the channelling mode, which has direct consequences for the validity of models describing the response of CaF2 to SHI irradiation. Furthermore, information about the elemental composition within the ion tracks is obtained using scanning TEM, electron energy loss spectroscopy, and with respect to the stoichiometry of the materials surface by in situ time of flight elastic recoil detection analysis. Advances in the analyses of the experimental data presented here pave the way for a better understanding of the ion track formation.

The influence of the CoFe2O4 nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe(2)O(4)/(100-x)SiO2 nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe2O4 nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 degrees C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe2O4 nanoparticles have spherical shapes and size in the 6-35 nm range. The Mossbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe2O4 nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.

Peculiarities of the magnetization reversal process in cylindrical Ni-Cu soft magnetic nanowires with dominant shape anisotropy are analyzed via both static and time dependent micromagnetic simulations. A reversible process involving acoherent-like spin rotation is always observed for magnetic fields applied perpendicularly to the easy axis whereas nucleation of domain walls is introduced for fields applied along the easy axis. Simple criteria for making distinction between a Stoner-Wohlfarth type rotation and a nucleation mechanism in systems with uniaxial magnetic anisotropy are discussed. Superposed reversal mechanisms can be in action for magnetic fields applied at arbitrary angles with respect to the easy axis within the condition of an enough strong axial component required by the nucleation. The dynamics of the domain wall, involving two different stages (nucleation and propagation), is discussed with respect to initial computing conditions and orientations of the magnetic field. A nucleation time of about 3 ns and corkscrew domain walls propagating with a constant velocity of about 150 m/s are obtained in case of Ni-Cu alloy (Ni rich side) NWs with diameters of 40 nm and high aspect ratio.

Aluminum Nitride (AlN) thin films were synthesized on Si (100) wafers at 450 degrees C by pulsed laser deposition. A polycrystalline AlN target was multipulsed irradiated in a nitrogen ambient, at different laser pulse repetition rate. Grazing Incidence X-Ray Diffraction and Atomic Force Microscopy analyses evidenced nanocrystallites with a hexagonal lattice in the amorphous AlN matrix. The thickness and optical constants of the layers were determined by infrared spectroscopic ellipsometry. The optical properties were studied by Fourier Transform Infrared reflectance spectroscopy in polarised oblique incidence radiation. Berreman effect was observed around the longitudinal phonon modes of the crystalline AlN component. Angular dependence of the A(1)LO mode frequency was analysed and connected to the orientation of the particles' optical axis to the substrate surface normal. The role of the laser pulse frequency on the layers' properties is discussed on this basis. (C) 2016 Elsevier B.V. All rights reserved.

Raman enhancement in a layered structure of Bib was studied under optical excitation near the edge of the fundamental absorption band. This phenomenon simultaneously appears at a low temperature with the generation of the excitonic photoluminescence (PL) band, unequally across the Raman spectrum, i.e. in the Stokes and anti-Stokes Raman branches, being dependent on the superposition of the excitation laser line to the excitonic emission band. Performed with the use of different resonant laser light excitations, this effect is regarded as a signature of the exciton-phonon interaction, which is interpreted in terms of a stimulated Raman scattering process (SRS), resulting from the mixing inside of the sample to two optical fields, the pump laser light and the excitonic PL light. (C) 2016 Elsevier B.V. All rights reserved.

Water soluble gold nanoparticles protected by lipoic acid were obtained and further functionalized by standard coupling reaction with 1-naphtylamine, 4-aminoantipyrine, and 4 0 -aminobenzo-15-crown-5 ether. Derivatives of lipoic acid with 1-naphtylamine, 4-aminoantipyrine, and 4 0 -aminobenzo-15-crown-5 ether were also obtained and characterized. All these were tested for their antimicrobial activity, as well as for their influence on mammalian cell viability and cellular cycle. In all cases a decreased antimicrobial activity of the obtained bioactive nanoparticles was observed as compared with the organic compounds, proving that a possible inactivation of the bioactive groups could occur during functionalization. However, both the gold nanoparticles as well as the functionalized bioactive nanosystems proved to be biocompatible at concentrations lower than 50 mu g/mL, as revealed by the cellular viability and cell cycle assay, demonstrating their potential for the development of novel antimicrobial agents.

The present work investigates the photocatalytical abatement of trichlorethylene (TCE) under simulated solar irradiation (AM 1.5). The employed catalytic materials, Au and Pd-Au nanoparticles supported on TiO2, were prepared by incipient wetness and by deposition-precipitation methods. It is found out that TCE is converted efficiently (>80%) to CI- and CO2 over all scrutinized catalysts. Typically, the metal addition enhances to some extent the photooxidation activity of TiO2 via photogenerated center dot OH radicals, electrons, and holes. The photocatalytic abatement of TCE over the same catalytic materials was examined in the presence of small amount of methanol. The idea was to convert TCE to Cl- and C-2 (ethane and ethylene) over Au and Pd-Au/TiO2 catalysts by the H-2 generated photocatalytically in situ. The experimental results evidenced that, over Pd-Au/TiO2 catalysts, hydrodechlorination (HDC) and photomineralization reactions of TCE occurs simultaneously. In contrast, Au/TiO2 is inactive to catalyze the hydrogenation of TCE. The results of TCE abatement by combined photooxidation/HDC reactions in presence of methanol are corroborated with H-2 photocatalytic generation results, over the same catalytic materials, from water/methanol mixture. A reaction mechanism is advanced in light of experimental results. The photo generated center dot OH radicals, electrons, and holes participate in a complex reaction pathway to formation of oxygenated organic intermediates, Cl-, CO2, and H-2. (C) 2016 Elsevier Inc. All rights reserved.