National Institute Of Materials Physics - Romania

A series of 3,4,5-tridodecyloxybenzyl pyridinium salts derived from 4-hydroxypyridine has been designed and prepared. The liquid crystalline properties of these compounds were investigated by polarized optical microscopy, differential scanning calorimetry and powder X-ray diffraction while their thermal stability was studied by thermogravimetric analysis. The N-3,4,5-tridodecyloxybenzyl-4-pyridone intermediate shows a monotropic columnar hexagonal mesophase ranging from 56 degrees C down to room temperature while the corresponding bromide dodecyl O-alkylated pyridinium salt shows one enantiotropic columnar mesophase and one additional monotropic columnar phase at lower temperatures. Replacing bromide ion (Br-) with other counterions (NO3-, BF4- and PF6-) resulted in mesophase suppression. These luminescent pyridinium salts show weak emission in dichloromethane solutions at room temperature and a pronounced red-shifted emission in solid state. Photoluminescent properties of the pyridinium salts do not depend significantly on the nature of counterion employed. (C) 2014 Elsevier B.V. All rights reserved.

The aim of this research is to prepare amorphous thin films of undoped gallium sulphide and doped with rare-earth sulphides, of rare-earth sulphides and to investigate their physical properties. We have prepared thin amorphous films of Ga2S3, EuS, Er2S3, Gd2S3, and Ga2S3 doped with rare-earth sulphides (Ga2S3:EuS, Ga2S3:Er2S3, Ga2S3:Gd2S3) by Pulsed laser Deposition (PLD). The corresponding targets for preparation of amorphous thin films were obtained by Spark Plasma Sintering (SPS) from commercially available powders of binary sulphides. The structural results for the undoped and doped Ga2S3 thin films indicate a packing of disordered layers similar to that of amorphous As2S3. Femtosecond laser irradiation of the Ga2S3 thin films shows a photoexpansion effect at low laser power (85-100 mW) and an ablation effect at higher laser power (above 105 mW). The threshold between low power and high power pulses is situated at higher value for Ga2S3 (100 mW) in comparison with the case of As2S3 thin films (20 mW). (C) 2014 Elsevier B.V. All rights reserved.

Fe-Ni graded films have been prepared by co-sputtering permalloy and Fe targets at different time-power sequences. Morpho-structural and magnetic investigations have been performed by transmission electron microscopy, Xray reflectometry, conversion electron Mossbauer spectroscopy and magneto-optic Kerr effect vector magnetometry, proving the thickness dependence of the properties. A magnetization reversal involving the displacement of Bloch-type walls is characteristic for a 115 nm thick Fe-Ni graded film whereas an in-plane coherent rotation of the spins, according to a Stoner-Wohlfarth mechanism was evidence for a 23 nm thick Fe-Ni graded film.

We report the fabrication of biofunctionalized magnetite core/sodium lauryl sulfate shell/antibiotic adsorption-shell nanoparticles assembled thin coatings by matrix assisted pulsed laser evaporation for antibacterial drug-targeted delivery. Magnetite nanoparticles have been synthesized and subsequently characterized by transmission electron microscopy and x-ray diffraction. The obtained thin coatings have been investigated by FTIR and scanning electron microscope, and tested by in vitro biological assays, for their influence on in vitro bacterial biofilm development and cytotoxicity on human epidermoid carcinoma (HEp2) cells.

The content of defects in Bi4Ge3O12 (BGO) glass-ceramic materials together with their ordering during crystallization induces ferromagnetic behaviours in these materials. The observed ferromagnetism has to be associated strictly with the GeO4 related defects in the atypical amorphous phase. The photoluminescence of BGO glass-ceramic materials can give useful information about the nature of defects, especially the oxygen vacancies from the GeO4 tetrahedra and Bi4Ge3O12 cubic structures. The concentration of these defects depends on annealing between 600 degrees C and 700 degrees C where orthorhombic and cubic phases coexist. The magnetization at saturation is higher in the samples dominated by the amorphous phase and the strength of the exchange interaction is higher in the samples dominated by the cubic phase, obtained over 700 degrees C, when the GeO4 tetrahedra are rearranged during crystallization together with their oxygen vacancies. (C) 2014 Elsevier B.V. All rights reserved.

Two new coordination polymers have been assembled using the chromato ions as bridging ligands: (1)(infinity)[Ni(phen)(H2O)(2)(mu-O2CrO2)] 1, and (3)(infinity)[Mn(4,4'-bipy)(H2O)(mu-O3CrO)]center dot H2O 2. In crystal 1 the chromate ions act as bridges connecting two nickel ions through two oxygen atoms, resulting in infinite chains. 1,10-Phenanthroline acts as a blocking ligand. In compound 2, each chromato ion is connected to three manganese ions, resulting in layers which are parallel to the ab plane. The layers are constructed from {Mn3Cr3} meshes, each metal atom being shared between three other meshes. The structure is expanded into the third direction by connecting the inorganic layers through 4,4'-bipy spacers. The thermal decomposition of the two compounds has been investigated. (C) 2014 Elsevier B.V. All rights reserved.

The magnetic properties of low filling factor Fe-nanoparticle monolayers separated by relatively thick Al2O3 layers were investigated in parallel and perpendicular external magnetic field. The thin film nanocomposites were prepared by sequential pulsed laser deposition on (100) Si substrates, and the monolayers contain single-domain, dispersive nanoparticles. When the magnetic field is oriented parallel to the layers, the composite exhibits superparamagnetism. However, in perpendicular field, the superferromagnetic order sets in, as revealed by the increase of the magnetic moment, the hysteresis persisting at high temperatures, and a smaller relaxation rate. The complex out of plane behavior of our nanocomposites in perpendicular field is attributed to quasi two-dimensionality and to the dispersion of the in-plane nanoparticle separation. (C) 2015 AIP Publishing LLC.

Rare-earth free (RE-free) exchange coupling nanocomposite magnets are intensively studied nowadays due to their potential use in applications demanding stable high-temperature operation and corrosion resistance. In this respect, the FePt alloy system is one of the most actively addressed potential permanent magnet solutions. In FePt alloys, promising magnetic features arise from the co-existence of hard magnetic L1(0) FePt and soft magnetic L1(2) Fe3Pt phases emerged from the same metastable precursor. The present work deals with an in-situ temperature-resolved synchrotron radiation study of the thermal stability, thermal expansion and microstructure evolution in exchange-coupled FePtAgB alloys. The as-cast microstructural state as well as the optimized magnetic behavior are given as reference and correlated to the observed microstructural evolution with temperature. The melt-spun Fe48Pt28Ag6B18 alloy ribbons were examined in situ by synchrotron X-ray powder diffraction from ambient temperature up to 600 degrees C. The FePt-Fe3Pt exchange-coupled microstructure achieved by rapid solidification is not significantly altered during the high temperature exposure. The thermal expansion of the FePt L1(0) unit cell has been found to be strongly anisotropic, being essentially an in-plane expansion which may be seen as an anisotropic invar effect. For the FePt L1(0) phase, a significant deviation from linear thermal expansion is observed at the Curie temperature T-C = 477 degrees C. This non-linear behavior above T-C is tentatively linked to a diffusion/segregation mechanism of Ag. The promising hard magnetic properties as well as the direct formation of the L1(0) phase from the as-cast state are directly related to the presence of Ag in the intergranular regions. (C) 2014 Elsevier B.V. All rights reserved.