National Institute Of Materials Physics - Romania

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5714 articles found

1781. GeO2-added MgB2 superconductor obtained by Spark Plasma Sintering

Authors: Batalu, D; Aldica, G; Popa, S; Kuncser, A; Mihalache, V; Badica, P

Published: OCT 2015, SOLID STATE SCIENCES, 48, 30, DOI: 10.1016/j.solidstatesciences.2015.06.013

Dense samples (relative density > 93%) of bulk MgB2 with GeO2 additions were obtained by Spark Plasma Sintering. The critical current density J(c) of the added samples is improved at high magnetic fields when compared to the pristine sample. The optimum composition is for MgB2(GeO2)(0.005). For this sample, a J(c)(20 K) = 10(2) A/cm(2) is obtained at 5.1 T versus 3.9 T for the pristine sample. Ge substitution in the crystal lattice of MgB2 can be considered negligible, and T-c,T-onset and T-c,T-midpoint from magnetization measurements scatter within 0.2 and 0.6 K, respectively. TEM investigations show some specific details at nano scale: the tendency to form secondary phases (25-100 nm) with sphere-like or irregular shapes is observed and discussed. Samples are composites and the residual strain of MgB2 is constant for pristine and GeO2-added samples. Therefore, pinning enhancement leading to improvement of Jc for the GeO2 added samples is purely a 'microstructure' effect due to the presence of secondary phases. The point pinning is determined to be the predominant mechanism. Addition of a higher amount of GeO2 is shifting the pinning mechanism toward a grain boundary pinning. (C) 2015 Elsevier Masson SAS. All rights reserved.

1782. Effect of rare earth substitution in cobalt ferrite bulk materials

Authors: Bulai, G; Diamandescu, L; Dumitru, I; Gurlui, S; Feder, M; Caltun, OF

Published: SEP 15 2015, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 390, 131, DOI: 10.1016/j.jmmm.2015.04.089

The study was focused on the influence of small amounts of rare earth (RE=La, Ce, Sm, Gd, Dy, Ho, Er, Yb) addition on the microstructure, phase content and magnetic properties of cobalt ferrite bulk materials. The X-Ray diffraction measurements confirmed the formation of the spinel structure but also the presence of secondary phases of RE oxides or orthoferrite in small percentages (up to 3%). Density measurements obtained by Archimedes method revealed a similar to 1 g cm(-3) decrease for the RE doped cobalt ferrite samples compared with stoichiometric one. Both the Mossbauer and Fourier Transform Infrared Spectrocopy analysis results confirmed the formation of the spinet phase. The saturation magnetization and coercive field values of the doped samples obtained by Vibrating Sample Magnetometry were close to those of the pure cobalt ferrite. For magnetostrictive property studies the samples were analyzed using the strain gauge method. Higher maximum magnetostriction coefficients were found for the Ho, Ce, Sm and Yb doped cobalt ferrite bulk materials as related to the stoichiometric CoFe2O4 sample. Moreover, improved strain derivative was observed for these samples but at higher magnetic fields due to the low increase of the coercive field values for doped samples. (C) 2015 Elsevier B.V. All rights reserved.

1783. Field - dipole interactions in L-cysteine-thiolate self assembled at p- and n-GaAs(100) electrodes

Authors: Lazarescu, V; Toader, AM; Enache, M; Preda, L; Anastasescu, M; Dobrescu, G; Negrila, C; Lazarescu, MF

Published: SEP 10 2015, ELECTROCHIMICA ACTA, 176, 124, DOI: 10.1016/j.electacta.2015.06.121

L-cysteine-thiolate monolayers spontaneously self-assembled on p- and n-GaAs(100) electrodes have been investigated by electrochemical impedance spectroscopy in H2SO4 solutions. On p-doped samples a potential-induced reversible proton transfer occurs within the L-cysteine-thiolate layer during both forward and backward potential scans; in contrast, on n-doped samples it is observed only in the reverse scan. The XPS data and the fractal analysis of the AFM images point to the field - dipole interactions operating distinctively in the L-cysteine-thiolate layer formed at p-and n-doped semiconducting substrates as the origin of the observed difference. The interaction of this small but highly polar molecule with the electrostatic field driven by the diffuse distribution of the excess charge in the semiconductor subsurface region both in equilibrium and under polarization conditions turned out to play a key role in determining the optimal orientation of the two polar groups. The latter one seems to be a prerequisite for the potential-induced internal proton transfer. (C) 2015 Elsevier Ltd. All rights reserved.

1784. Time delay and excitation mode induced tunable red/near-infrared to green emission ratio of Er doped BiOCl

Authors: Avram, D; Florea, M; Tiseanu, I; Tiseanu, C

Published: SEP 9 2015, , DOI: 10.1088/0022-3727/48/35/355501

1785. Deoxygenation of oleic acid: Influence of the synthesis route of Pd/mesoporous carbon nanocatalysts onto their activity and selectivity

Authors: Dragu, A; Kinayyigit, S; Garcia-Suarez, EJ; Florea, M; Stepan, E; Velea, S; Tanase, L; Colliere, V; Philippot, K; Granger, P; Parvulescu, VI

Published: SEP 5 2015, , DOI: 10.1016/j.apcata.2015.01.008

1786. Optical properties of Mn doped ZnO films and wires synthesized by thermal oxidation of ZnMn alloy

Authors: Sima, M; Mihut, L; Vasile, E; Sima, M; Logofatu, C

Published: SEP 1 2015, THIN SOLID FILMS, 590, 147, DOI: 10.1016/j.tsf.2015.07.072

Mn doped ZnO films and wires, having different manganese concentrations were synthesized by thermal oxidation of the corresponding ZnMn alloy films and wires electrodeposited on a gold substrate. Structural and optical properties were addressed with scanning electron microscopy, X-ray diffraction (XRD), Raman scattering and photoluminescence (PL). To estimate the manganese concentration in Mn doped ZnO films, X-ray photoelectron spectroscopy was used. XRD patterns indicate that the incorporation of Mn2+ ions into the Zn2+ site of ZnO lattice takes place. Quenching of the ZnO PL appears due to Mn2+ ions in the ZnO lattice. Moreover, a significant decrease in the green emission of ZnO is reported in the case of the Mn doped ZnO wire array with a Mn concentration of 1.45%. The wurtzite ZnO has a total of 12 phonon modes, namely, one longitudinal acoustic (LA), two transverse acoustic (TA), three longitudinal optical (LO), and six transverse optical branches. Compared to the undoped ZnO, a gradual up-shift of the Raman lines assigned to the 2LA and A(1) (LO) vibrational modes, from 482 and 567 cm(-1) to 532 and 580 cm(-1), respectively, takes place for the Mn doped ZnO films having a Mn concentration between 2 and 15%. Additionally, in the case of the Mn doped ZnO films with 7 and 15% Mn concentration, Raman spectra show the appearance and increase in the relative intensity of the ZnO Raman line assigned to the TA + LO vibrational mode in the 600-750 cm(-1) spectral range. For the Mn-doped ZnO wires, the presence of the Raman line peaking at 527 cm(-1) confirms the insertion of Mn2+ ions in ZnO lattice. (C) 2015 Elsevier B.V. All rights reserved.

1787. Heterogeneous Gold Catalyst: Synthesis, Characterization, and Application in 1,4-Addition of Boronic Acids to Enones

Authors: Moragues, A; Neatu, F; Parvulescu, VI; Marcos, MD; Amoros, P; Michelet, V

Published: SEP 2015, ACS CATALYSIS, 5, 5067, DOI: 10.1021/acscatal.5b01207

The new 1 wt % Au/TiO2-UVM-7 catalyst was prepared and fully characterized. This heterogeneous catalyst proved to be active, selective and recyclable for the unprecedented gold-catalyzed 1,4-addition of various functionalized arylboronic acids to 2-cyclohexen-1-one and other selected enones using toluene as a solvent. The gold-based catalyst was recycled two times and played an active role in this reaction, and the nature of the solvent determined a remarkable change in the products' selectivities.

1788. Physicochemical Characterization and In Vitro Cytotoxic Effect of 3-Hydroxyflavone in a Silver Nanoparticles Complex

Authors: Voicescu, M; Craciunescu, O; Moldovan, L; Anastasescu, M; Angelescu, DG; Teodorescu, VS

Published: SEP 2015, JOURNAL OF FLUORESCENCE, 25, 1223, DOI: 10.1007/s10895-015-1608-z

The aim of this work was to characterize the physico-chemical properties of 3-hydroxyflavone (3-HF) in a silver nanoparticles complex (SNPs) using UV-vis and Fluorescence spectroscopy, Atomic Force Microscopy (AFM) and Transmission Electron Microscopy (TEM) analysis. One also evaluated its effect on the cell viability and morphology of L929 mouse fibroblast cells in vitro. The contribution of the carrier protein, Bovine Serum Albumin (BSA) to 3-HF properties has also been investigated. 3-HF in BSA/SNPs systems presented no cytotoxic effect in L929 mouse fibroblast cells at any of the tested concentrations. The results are discussed with relevance to the oxidative stress process.

1789. Intense heavy ion beam-induced temperature effects in carbon-based stripper foils

Authors: Kupka, K; Tomut, M; Simon, P; Hubert, C; Romanenko, A; Lommel, B; Trautmann, C

Published: SEP 2015, JOURNAL OF RADIOANALYTICAL AND NUCLEAR CHEMISTRY, 305, 882, DOI: 10.1007/s10967-015-4057-x

At the future FAIR facility, reliably working solid carbon stripper foils are desired for providing intermediate charge states to SIS18. With the expected high beam intensities, the foils experience enhanced degradation and limited lifetime due to severe radiation damage, stress waves, and thermal effects. This work presents systematic measurements of the temperature of different carbon-based stripper foils (amorphous, diamond-like, and carbon-nanotube based) exposed to 4.8 MeV/u U, Bi, and Au beams of different pulse intensities. Thermal and spectroscopic analyses were performed by means of infrared thermography and Fourier transform infrared spectroscopy. The resulting temperature depends on the foil thickness and strongly increases with increasing pulse intensity and repetition rate.

1790. 1D-polyaniline starting from self-assembled systems

Authors: Donescu, D; Ghiurea, M; Spataru, CI; StIng, G; Anghel, D; Baibarac, M; Baltog, I

Published: SEP 2015, COLLOID AND POLYMER SCIENCE, 293, 2524, DOI: 10.1007/s00396-015-3645-1

The radical polymerization of aniline hydrochloride (ANIHCl) in the presence of ammonium persulfate was studied. 1D-Polyaniline (PANI) with fibrillar morphologies was obtained in the presence of anionic surfactants. The changes of the PANI-template structures in aqueous solution were studied using static fluorescence measurements. The dispersed PANI nanoparticles were characterized using dynamic light scattering, scanning electron microscopy (SEM), and Raman and Fourier transform infrared spectroscopies. The thermal analysis and the electrical conductivity of the dried samples were also performed. The fluorescence measurements indicated that nanocrystals of ANIHCl form in water complexes with the anionic surfactants at smaller concentrations than the critical micellar concentration. The same method revealed that other organic complexes with sulfonate groups do not induce an increase of the hydrophobic region due to short hydrocarbon tails. The SEM micrographs and Raman spectra revealed that the PANI nanofibers are compact and different compared to the nanoparticles prepared without surfactants.