National Institute Of Materials Physics - Romania

Amorphous Bi4Ge3O12 glass samples were produced by melt quenching procedure stating with Bi4Ge3O12 (BGO) powder, obtained by solid state reaction between oxides. The kinetics of non-isothermal crystallization of EGO nano-crystals has been investigated. Differential Thermal Analysis (DTA) can give the main parameters of crystallization with an exothermic peak from 813 K to 851 K depending on the heating rate, which was assigned to the crystallization of cubic BGO in the amorphous matrix and compared with the X-Ray Diffraction (XRD) patterns. The nano-crystal dimensions were calculated from the XRD patterns by using the Debye-Scherrer method and were compared with Transmission Electron Microscopy (TEM) images. It was shown that the Ozawa model is most suitable for describing the behavior of non-isothermal crystallization of EGO nano-crystals within the glass matrix. Experimental results suggest a disk-shape type growth mechanism for the Bi4Ge3O12 nano-crystallites. The Flynn-Wall-Ozawa method has shown that the average activated energy value is 385 +/- 14 kJ/mol which was computed within the same model and agrees very well with the activation energy of the crystallization. (C) 2012 Elsevier B.V. All rights reserved.

Superconducting bulks of MgB2 with addition of Sb2O3 and Sb with different stoichiometric compositions ((MgB2) + (Sb2O3) (x) , x = 0.0025, 0.005, 0.015, and (MgB2) + (Sb)(y), y = 0.01) were obtained by the Spark Plasma Sintering (SPS) technique. All added samples have high density, above 95% and critical temperature, T (c), of 38.1-38.6 K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. Impurity phases are Mg3Sb2, MgO, and MgB4. The optimum addition is Sb2O3 for x = 0.005. This sample shows the critical current density, J (c)(5 K, 0 T) = 4 x 10(5) A/cm(2) and J (c)(5 K, 7 T) = 6 x 10(2) A/cm(2), while the irreversibility field, H (irr) (5 K, 100 A/cm(2)) = 8.23 T. Indicated values of J (c) and H (irr) are higher than for the pristine sample. The mechanism of J (c) and H (irr) increase in the Sb2O3 added samples is complex and composed of opposite effects most probably involving morphology elements, the presence of nano metric MgB4 and the indirect influence of oxygen or oxygen and Sb. Crystallite size of MgB2 is decreasing when Sb-based additions are introduced and the effect is stronger for the Sb-metal addition. The sample with Sb-metal addition does not improve J (c) and H (irr) when compared with pristine sample.

Photoluminescence and magnetic circular dichroism of the IrQ(ppy)(2)-5Cl compound were investigated between 15 and 295 K. These results have been compared with the output files obtained from Density Functional Theory by using the Gaussian 03W software and some additional packages. The experimental results confirm the first triplet state absorption which arises from d to pi(Q) transition. The temperature dependence photoluminescence have shown a small interaction with the polystyrene, used for dispersion of IrQ(ppy)(2)-5Cl compound. The green and red phosphorescence have the same temperature dependence. The MCD spectra, especially at 15K, reveals the main transitions involved in the Metal-to-Ligand Charge Transfer processes from the Ir towards the two ligands, phenylpyridine and quinoline, respectively. (C) 2011 Elsevier B.V. All rights reserved.

Te metal or TeO2 were added to MgB2 ((MgB2) (A)(x), x = 0.005, 0.01, 0.03, A = addition). The mixtures were processed by spark plasma sintering. The critical current density J(c), of the samples containing the Te/TeO2 additions is enhanced at high fields and at temperatures up to 20K. The curve of J(c)(5 K, H) for the sample with optimum x(Te) = 0.01 shows no accelerated decrease up to 8 T (J(c)(5 K, 8 T) = 1.8 x 10(3) A cm(-2)). The irreversibility field of the samples containing the Te/TeO2 additions is also enhanced. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Carbon nanowalls (CNWs) functionalization allows the tailoring of some of their properties after they have been synthesized. Herewith we report on post-synthesis CNWs functionalization by plasma treatments. Radiofrequency plasmas generated in hydrogen, oxygen, nitrogen, tetrafluoroethane, and sulfur hexafluoride admixed to argon, were used. The changes of morphology, structure, chemical composition were determined by SEM, FTIR, Raman Spectroscopy, specifically for each gas mixture. The results point out to the surface erosion, the functional groups attachment, or to thin film coverage of CNWs material. Such processes strongly influence the material properties, as exemplified by the wettability: superhydrophilic or superhydrophobic surfaces are obtained starting from the same base CNWs material.

The phase of the electronic wave function is not directly measurable but, quite remarkably, it becomes accessible in pairs of isospectral shapes, as recently proposed in the experiment by Moon et al. [Science 319, 782 (2008)]. The method is based on a special property, called transplantation, which relates the eigenfunctions of the isospectral pairs, and allows us to extract the phase distributions, if the amplitude distributions are known. We numerically simulate such a phase extraction procedure in the presence of disorder, which is introduced both as Anderson disorder and as roughness at edges. With disorder, the transplantation can no longer lead to a perfect fit of the wave functions, however we show that a phase can still be extracted-defined as the phase that minimizes the misfit. Interestingly, this extracted phase coincides with (or differs negligibly from) the phase of the disorder-free system, up to a certain disorder amplitude, and a misfit of the wave functions as high as similar to 5%, proving a robustness of the phase extraction method against disorder. However, if the disorder is increased further, the extracted phase shows a puzzle structure, no longer correlated with the phase of the disorder-free system. A discrete model is used, which is the natural approach for disorder analysis. We provide a proof that discretization preserves isospectrality and the transplantation can be adapted to the discrete systems.

Background: In this work the chemical structure of dextran-iron oxide thin films was reported. The films were obtained by MAPLE technique from composite targets containing 10 wt. % dextran with 1 and 5 wt.% iron oxide nanoparticles (IONPs). The IONPs were synthesized by co-precipitation method. A KrF* excimer laser source (lambda = 248 nm, tau(FWHM)congruent to 25 ns, nu = 10 Hz) was used for the growth of the hybrid, iron oxide NPs-dextran thin films. Results: Dextran coated iron oxide nanoparticles thin films were indexed into the spinel cubic lattice with a lattice parameter of 8.36 angstrom. The particle sized calculated was estimated at around 7.7 nm. The XPS shows that the binding energy of the Fe 2p(3/2) of two thin films of dextran coated iron oxide is consistent with Fe3+ oxides. The atomic percentage of the C, O and Fe are 66.71, 32.76 and 0.53 for the films deposited from composite targets containing 1 wt.% maghemite and 64.36, 33.92 and 1.72 respectively for the films deposited from composite targets containing 5 wt.% maghemite. In the case of cells cultivated on dextran coated 5% maghemite gamma-Fe2O3, the number of cells and the level of F-actin were lower compared to the other two types of thin films and control. Conclusions: The dextran-iron oxide continuous thin films obtained by MAPLE technique from composite targets containing 10 wt.% dextran as well as 1 and 5 wt.% iron oxide nanoparticles synthesized by co-precipitation method presented granular surface morphology. Our data proved a good viability of Hep G2 cells grown on dextran coated maghemite thin films. Also, no changes in cells morphology were noticed under phase contrast microscopy. The data strongly suggest the potential use of iron oxide-dextran nanocomposites as a potential marker for biomedical applications.

Iron oxide oxide nanoparticles were prepared by chemical co-precipitation method. The nanoparticles were mixed with dextran in distilled water. The obtained solutions were frozen in liquid nitrogen and used as targets during matrix assisted pulsed laser evaporation for the growth of hybrid, iron oxide nanoparticles-dextran thin films. Fourier Transform Infrared Spectroscopy and X-ray diffraction investigations revealed that the obtained films preserve the structure and composition of the initial, non-irradiated iron oxide-dextran composite material. The biocompatibility of the iron oxide-dextran thin films was demonstrated by 3-(4.5 dimethylthiazol-2yl)-2.5-diphenyltetrazolium bromide-based colorimetric assay, using human liver hepatocellular carcinoma cells. (C) 2011 Elsevier B.V. All rights reserved.

This paper discusses the properties of two arylenevinylene oligomers thin films deposited by vacuum evaporation on different substrates. The morphology of the thin films was investigated by scanning electron microscopy and atomic force microscopy, and the optical properties by UV-Vis and fluorescence spectroscopy. The optical nonlinear phenomenon of two-photon absorption induced fluorescence has been evidenced in the thin films of these compounds. We have also investigated the electrical properties of semiconductor/insulator/semiconductor (ITO/oligomer/Si) heterostructures in correlation with the contact energetic barriers, morphological and structural properties of the layers. (C) 2011 Elsevier B.V. All rights reserved.

The article reports on the tilted growth of textured aluminium nitride thin films obtained by radio-frequency magnetron sputtering onto 50 mm diameter Si (111) wafers, in reactive atmosphere, in a planar sputtering system without tilting the substrate and with no additional sputtering geometry alterations. The films were investigated using, X-ray diffraction, spectroscopic ellipsometry and scanning electronic microscopy, done by local measurements on the wafer surface, at different distances from the centre. A progressive increase of the tilt angle when moving away from the sample centre has been found. The maximum tilt angle of the columnar AlN crystallites, obtained near the edges of the wafer, is about 7 degrees. The results showed also that tilting is associated with smaller thickness and larger dispersion of the c axis orientation. Synthesizing inclined c axis AlN films should allow the fabrication of surface acoustic wave devices based on shear waves for liquid sensor applications.