National Institute Of Materials Physics - Romania

We present the effect of single molecular magnet ([Fe(bpca) Dy-2(NO (3))(4)] a <...H (2) Oa <...4.5 CH (3) NO (2) and [Mn (2)(naften) (2)(CH 3COO)(CH 3OH)] a <...BPh (4)) thermolysis on the superconducting properties of polycrystalline MgB (2) samples when inserted and sintered by spark plasma sintering technique. As a result of pyrolysis, Fe- and Dy-magnetic compounds grow within the MgB (2) matrix and give a paramagnetic behavior in normal state, whereas the Mn-based compounds display negligible magnetic properties. We find that the magnetic critical current density of the as-obtained superconducting composites, as well as the pinning mechanism, is dependent on the magnetic background, with a noticeable advantage for the sample with magnetic compounds.

Voltage and frequency dependent capacitance measurements were performed on epitaxial BaTiO3 and Pb(Zr0.2Ti0.8)O-3 thin films deposited on single crystal SrTiO3 substrates with (001) and (111) orientations. The measured capacitors have common bottom SrRuO3 contact and different metals as top electrodes: SrRuO3, Pt, Cu, Al, and Au. The capacitance-voltage characteristics were used to extract information regarding the density of the free carriers and the linear contribution to the static dielectric constant. The frequency dependent impedance was used to develop a suitable equivalent circuit for the epitaxial ferroelectric capacitors. It was found that the frequency dependence of the imaginary part of the impedance can be well simulated, in all cases, using a circuit composed of Schottky-type capacitance related to electrode interfaces, contact resistance, and the R-C parallel connection related to the ferroelectric volume of the film. Values for the components of the equivalent circuit were obtained by fitting the experimental data with the simulated curves. These were then used to extract quantities such as dielectric constant in the ferroelectric volume, the width of the depletion layers, and the apparent built-in potential. It was found that, although the investigated capacitors are of different ferroelectric materials, grown on substrates with different orientations, and having different metals as top electrodes, the values for the capacitance associated with the Schottky contacts and the apparent built-in potential are not very different. The results suggest a strong influence of ferroelectric polarization on the electrode interface properties in the case of epitaxial ferroelectric films. (C) 2014 AIP Publishing LLC.

Indium oxide thin films were grown by pulsed electron beam deposition method at 500 Con c-cut sapphire and (0 0 1) oriented LaAlO3 single crystal substrates in oxygen or argon gas. The effects of ambient gas and substrate symmetry on the growth of indium oxide thin films were studied. Stoichiometric In2O3 films are formed in oxygen, while oxygen deficient In2O2.5 films are grown in argon, with In metallic nanoclusters embedded in a In2O3 matrix (nanocomposite films). In both cases, epitaxial In2O3 films having the bixbyite phase were grown with various orientation relationships, depending upon the substrate symmetry and gas ambient (oxygen or argon). Domain matching epitaxy was used to describe the precise in-plane epitaxial film-substrate relationships. The differences in film texture were correlated to the differences in growth conditions, while the differences in the film properties were correlated to the film oxygen composition. (c) 2014 Elsevier B.V. All rights reserved.

Thin films of C layers were deposited by radiofrequency magnetron sputtering on silicon substrates using three gaseous atmospheres: pure Ar, Ar + H-2 and Ar + D-2 mixtures. Scanning Electron Microscopy investigations showed that addition of D-2 or H-2 to main sputtering gas (Ar) leads to the enhancement of the deposition rate while the layer morphology remained columnar. Fourier Transform Infrared Spectroscopy measurements revealed the presence of D-C or H-C chemical bonds in the samples. Ion beam analysis measurements performed by simultaneous recording of the recoiled H and D ions, and of backscattered He-4 confirmed the incorporation of hydrogen and deuterium in the deposited carbon thin films. (C) 2014 Elsevier B.V. All rights reserved.

In this paper, we analyze the structural distortions observed by transmission electron microscopy in thin epitaxial SrRuO3 layers used as bottom electrodes in multiferroic coatings onto SrTiO3 substrates for future multiferroic devices. Regardless of the nature and architecture of the multilayer oxides deposited on the top of the SrRuO3 thin films, selected area electron diffraction patterns systematically revealed the presence of faint diffraction spots appearing in forbidden positions for the SrRuO3 orthorhombic structure. High-resolution transmission electron microscopy (HRTEM) combined with Geometric Phase Analysis (GPA) evidenced the origin of these forbidden diffraction spots in the presence of structurally disordered nanometric domains in the SrRuO3 bottom layers, resulting from a strain-driven phase transformation. The local high compressive strain (-4% divided by -5%) measured by GPA in the HRTEM images induces a local orthorhombic to monoclinic phase transition by a cooperative rotation of the RuO6 octahedra. A further confirmation of the origin of the forbidden diffraction spots comes from the simulated diffraction patterns obtained from a monoclinic disordered SrRuO3 structure. (C) 2014 AIP Publishing LLC.

Zinc oxide-graphene oxide nanocomposite layers were submitted to laser irradiation in air or controlled nitrogen atmosphere using a frequency quadrupled Nd:YAG (lambda = 266 nm, tau(FWHM) congruent to 3 ns, nu = 10 Hz) laser source. The experiments were performed in air at atmospheric pressure or in nitrogen at a pressure of 2 x 10(4) Pa. The effect of the irradiation conditions, incident laser fluence value, and number of subsequent laser pulses on the surface morphology of the composite material was systematically investigated. The obtained results reveal that nitrogen incorporation improves significantly the wetting and photoactive properties of the laser processed layers. The kinetics of water contact angle variation when the samples are submitted to laser irradiation in nitrogen are faster than that of the samples irradiated in air, the surfaces becoming super-hydrophilic under UV light irradiation. (C) 2014 AIP Publishing LLC.

Ge, GeO2 and Ge2C6H10O7 additions to MgB2 obtained by ex situ spark plasma sintering significantly enhance the critical current density J(c) in high magnetic fields. A J(c)(T = 20 K) of 102 A cm(-2) is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB2(Ge2C6H10O7)(0.0014) sample. The decrease in the critical temperature for added samples is less than 1 K and T-c(20 K, H = 0) shows a small decrease from 5.5 x 10(5) A cm(-2) in the pristine sample to 3.9 x 10(5) A cm(-2) in MgB2(Ge2C6H10O7)(0.0014) sample. Ge does not substitute into the MgB2 lattice. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Thin SiC films were grown on (1 0 0) Si substrates at temperatures from 400 to 1000 degrees C under various CH4 pressures by the pulsed laser deposition (PLD) technique using a KrF excimer laser. After deposition, films were in situ annealed at their deposition temperature under 500 mbar of CH4 for 1.0-1.5h. X-ray reflectivity investigations showed that films exhibited mass densities similar to SiC single crystal samples, while symmetrical and grazing incidence X-ray diffraction investigations found that films deposited at 800 degrees C or higher substrate temperatures were nanocrystalline. Modeling of spectroscopic ellipsometry measurements indicated that the refractive index values were similar to those reported for bulk SiC, while X-ray photoelectron spectroscopy investigations found that films contained in bulk a relatively low oxygen concentration of around 1.0 at.%. Nanoindentation results showed that the deposited SiC films were very hard, with hardness values above 40 GPa for films deposited at temperatures higher than 800 degrees C. (C) 2014 Elsevier B.V. All rights reserved.

We investigate the effect of silver addition to polycrystalline Sm-1111 superconductor. We show that Ag improves the phase homogeneity of the samples drastically reducing the weight of the low temperature, hence, leading to less fluorinated phases. The intragranular critical current density is enhanced by adding a small amount of Ag in all pinning regimes but a higher content of Ag leads to a decrease of this quantity. A tentative explanation for this dependence is proposed.

The cathodic deposition of zinc oxide film on Pt from an aqueous solution containing 0.05 M Zn(NO3)(2) was investigated using linear sweep voltammetry and electrochemical impedance spectroscopy. The film formation is an electroprecipitation process due to reduction of nitrate ion on the surface of working electrode in the presence of Zn2+ ions. A morphology of ZnO with hexagonal platelets was observed. The standard electromotive force of the cell reaction was calculated for both NO3/NO2 process and overall deposition process. Linear voltammograms and visual observations showed that polarizing the electrode at higher negative potentials than -1.1 V, the parallel reduction of zinc ion to zinc metal occurs together with reduction of nitrate ion to hydroxide ion; as a consequence, a partial amorphous state of ZnO film was recorded on SEM micrographs. Experimental impedance data and data calculated by fitting with an equivalent circuit showed that the ZnO formation involves an adsorption of complexed zinc ions on Pt electrode, before the charge transfer.