National Institute Of Materials Physics - Romania

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860 articles found

461. Cu codoping control over magnetic precipitate formation in ZnCoO nanowires

Authors: Granville, S; Matei, E; Enculescu, I; Toimil-Molares, ME

Published: DEC 22 2014, APPLIED PHYSICS LETTERS, 105, DOI: 10.1063/1.4904987

Using electrodeposition, we have grown nanowires of ZnCoO with Cu codoping concentrations varying from 4-10 at. %, controlled only by the deposition potential. We demonstrate control over magnetic Co oxide nano-precipitate formation in the nanowires via the Cu concentration. The different magnetic behavior of the Co oxide nano-precipitates indicates the potential of ZnCoO for magnetic sensor applications. (C) 2014 AIP Publishing LLC.

462. Structural characteristics of iridium dual-emitter organometallic compound

Authors: Polosan, S; Ciobotaru, IC; Enculescu, I; Ciobotaru, CC

Published: DEC 14 2014, JOURNAL OF MATERIALS RESEARCH, 29, 2904, DOI: 10.1557/jmr.2014.337

By combining two types of ligands, phenylpyridine and quinoline, a new type of organometallic IrQ(ppy)(2) compound has been synthesized, which exhibits two phosphorescences: green and red. Using an appropriate catalyst, the final IrQ(ppy)(2) compound has a good chemical yield up to 60% and becomes a stable dual emitter at room temperature. This compound is important because it exhibits stable red emission which is limited by the quantum yield due to the low energy band gap. As a result, an overlap between the ground state and the excited state occurs due to the vibrations that increase the nonradiative transitions, destroying the red emissions. Structural characteristics of the IrQ(ppy)(2) powder reveal a triclinic structure confirmed by x-ray diffraction and scanning electron microscopy images. Thermal analysis of the final compound confirms a good stability against decomposition and structural changes up to 350 degrees C. X-ray photoelectron spectroscopy reveals Ir-O chemical bonds and several differences between the intermediate and final compounds, such as Ir-Cl bonds. Cathodoluminescence patterns show a phosphorescent triclinic structure with a higher efficiency for the red color. Backscattering electron images prove that there is a uniform distribution of iridium ions in the IrQ(ppy)(2) nanocrystals.

463. Biocatalytic designs for the conversion of renewable glycerol into glycerol carbonate as a value-added product

Authors: Tudorache, M; Ghemes, G; Nae, A; Matei, E; Mercioniu, I; Kemnitz, E; Ritter, B; Coman, S; Parvulescu, VI

Published: DEC 2014, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 12, 1270, DOI: 10.2478/s11532-014-0547-x

A comparative study of two different biocatalytic models, e.g. enzyme immobilized on magnetic particles (EIMP) and cross-linking enzyme aggregates onto magnetic particles (CLEMPA) was performed. The first model was designed as enzyme-immobilized on the magnetic particles surface (EIMP). The second model was constructed as a network structure with the enzyme aggregates and magnetic particles placed into the nodes and polyglutaraldehyde cross-linker as the network ledges. The design was called cross-linking enzyme aggregates onto magnetic particles (CLEMPA). The biocatalysts were prepared using lipase enzyme from Aspergillus niger for catalyzing the glycerol (Gly) conversion to glycerol carbonate (GlyC). The biocatalyst characteristics for both designs (EIMP and CLEMPA) were evaluated using scanning electron microscopy (SEM), laser light scattering (LLS) and UV-Vis techniques. The EIMP model was strongly influenced by the composition of the polymeric layer covering the particles surface, while the size of the magnetic particles affected mostly the CLEMPA design. Also, the biocatalytic capacity of the tested models was evaluated as maximum 52% Gly conversion with 90% GlyC selectivity for EIMP, and 73% Gly conversion with 77% GlyC selectivity for CLEMPA. Both biocatalytic models were successfully used to prepare GlyC from "crude" glycerol collected directly from the biodiesel process (e.g. 49% Gly conversion with 91% GlyC selectivity for EIMP and 70% Gly conversion with 80% GlyC selectivity for CLEMPA).

464. Embedding of IrQ(ppy)(2) organometallic compounds in polypyrrole conducting polymer for OLED's applications

Authors: Ciobotaru, IC; Matei, E; Ciobotaru, CC; Polosan, S

Published: DEC 2014, SYNTHETIC METALS, 198, 328, DOI: 10.1016/j.synthmet.2014.10.041

Conducting polypyrrole:IrQ(ppy)(2) thin films were obtained by electrochemical method which ensure uniform dispersion of the organometallic in the polymer matrix. A thin layer of about 50 nm polypyrrole: IrQ(pPY)(2) thin films were deposited on the ITO/glass substrate and used for spectroscopic, structural, and electric characterization. The photoluminescence spectrum of polypyrrole:IrQ.(ppy)2 have shown the two main emissions of IrQ(ppy)(2) at 2.44 eV (508 nm) and 2 eV (620 nm) besides of the polypyrrole weak emission centered at 2.55 eV (485 nm). The electric conductivity of the doped polypyrrole thin layer has almost the same conductivity with the undoped polypyrrole thin film suggesting an homogenous polypyrrole:IrQ(ppy)(2) composite which can be used as emissive layer in the OLED's structures. (C) 2014 Elsevier B.V. All rights reserved.

465. Influence of morphology on the emissive properties of dye-doped PVP nanofibers produced by electrospinning

Authors: Enculescu, M; Evanghelidis, A; Enculescu, I

Published: DEC 2014, JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS, 75, 1371, DOI: 10.1016/j.jpcs.2014.07.008

Dye-doped polymer micro- and nanofibers with tailored light emission properties have great potential for applications in optical, optoelectronic, or photonic devices. In this study, these types of structures were obtained by electrospinning rhodamine 6 G-doped polyvinylpyrrolidone (PVP) using a polymer solution of 10% (mass) concentration in ethanol. Polymer nanofibers with different morphologies (smooth and beaded) and diameters of about 500 nm were obtained using different electrospinning conditions with the same solutions. Fluorescence optical microscopy observations showed that the dye was distributed uniformly in the doped PVP nanofibers. Different shifts were observed when we compared the wavelength of the dye emission band peak of the smooth nanofibers (566 nm) and the wavelength of the dye emission band peak of the beaded fibers (561.5 nm) produced by electrospinning in different conditions with the wavelength of the emission band peak for transparent thin films produced by spin coating (558 nm) using the same polymer solution. This demonstrates that it is possible to tune the optical properties of electrospun dye-doped polymer nanofibers simply by modifying the morphology of the material, i.e., the parameters of the electrospinning process. (C) 2014 Elsevier Ltd. All rights reserved.

466. The Influence of the Microstructure and Morphology of CeO2 Buffer Layer on the Properties of YBCO Films PLD Grown on Ni Tape

Authors: Mihalache, V; Stefan, N; Enculescu, I; Mihailescu, IN; Socol, M; Miroi, M

Published: NOV 2014, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 27, 2485, DOI: 10.1007/s10948-014-2679-9

YBa2Cu3O7-delta films were deposited on CeO2-buffered nickel substrates, with different buffer thickness. Full width at half maximum of rocking curve, Delta(omega), of CeO2 and yttrium barium copper oxide (YBCO), as well as the critical temperature, T-c, of YBCO were shown to be strongly dependent on buffer thickness. They behave similarly but not proportional to the buffer thickness increase. This and the fact that Delta(omega) vs. buffer thickness and T-c vs. buffer thickness for YBCO behave similar with RMS roughness vs. thickness of CeO2 indicates that the surface peculiarity of buffers is responsible for YBCO properties. More precisely, the surface of CeO2 films prepared by the chemical solution route based on propionic acid is prone to agglomerate (de-wet) and the degree of agglomeration depends in an intricate way on buffer thickness. We showed that nor RMS roughness neither (00l) texture degree can define alone the surface suitable for c-axis YBCO nucleation. The {111} faceted grains (even in the case of high (00l) texture) and other defects generated by agglomeration supply a low fraction of (00l) flat terminations of buffer that affect the nucleation of c-axis-oriented YBCO phase. Moreover, the thermal instability of the surface morphology of CeO2 buffers (further development of de-wetting process, {111} faceted grains, etc. during superconducting layer deposition) influence the quality of YBCO films.

467. Physical properties of AlxIn1-xN thin film alloys sputtered at low temperature

Authors: Besleaga, C; Galca, AC; Miclea, CF; Mercioniu, I; Enculescu, M; Stan, GE; Mateescu, AO; Dumitru, V; Costea, S

Published: OCT 21 2014, JOURNAL OF APPLIED PHYSICS, 116, DOI: 10.1063/1.4898565

In this paper, we report on the structural, optical, and electrical properties of a wide compositional range of AlxIn1-xN thin layers deposited on glass and polyethylene terephthalate substrates. AlxIn1-xN layers of controlled composition were obtained by a simple reactive magnetron co-sputtering protocol, using a single aluminium target with indium insets, by varying the Al/In target surface area ratio, and the composition of the deposition atmosphere. The relevant physical properties were investigated and discussed. It is shown that the texture of the thin films is dependent on the cation ratio, while the bowing parameters of lattice constants and band gap values are larger than those of epitaxial layers. (C) 2014 AIP Publishing LLC.

468. Systematic investigation and in vitro biocompatibility studies on mesoporous europium doped hydroxyapatite

Authors: Popa, CL; Ciobanu, CS; Iconaru, SL; Stan, M; Dinischiotu, A; Negrila, CC; Motelica-Heino, M; Guegan, R; Predoi, D

Published: OCT 2014, CENTRAL EUROPEAN JOURNAL OF CHEMISTRY, 12, 1046, DOI: 10.2478/s11532-014-0554-y

This paper reports the systematic investigation of europium doped hydroxyapatite (Eu:HAp). A set of complementary techniques, namely Fourier Transform Infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and the Brunauer-Emmett-Teller (BET) technique were used towards attaining a detailed understanding of Eu:HAp. The XPS analysis confirmed the substitution of Ca ions by Eu ions in the Eu:HAp samples. Secondly, Eu:HAp and pure HAp present type IV isotherms with a hysteresis loop at a relative pressure (P/P-0) between 0.4 and 1.0, indicating the presence of mesopores. Finally, the in vitro biological effects of Eu:HAp nanoparticles were evaluated by focusing on the F-actin filament pattern and heat shock proteins (Hsp) expression in HEK293 human kidney cell line. Fluorescence microscopy studies of the actin protein revealed no changes of the immunolabelling profile in the renal cells cultured in the presence of Eu:HAp nanoparticles. Hsp60, Hsp70 and Hsp90 expressions measured by Western blot analysis were not affected after 24 and 48 hours exposure. Taken together, these results confirmed the lack of toxicity and the biocompatibility of the Eu:HAp nanoparticles. Consequently, the possibility of using these nanoparticles for medical purposes without affecting the renal function can be envisaged.

469. Laser prepared organic heterostructures based on star-shaped arylenevinylene compounds

Authors: Stanculescu, A; Socol, G; Grigoras, M; Ivan, T; Vacareanu, L; Socol, M; Rasoga, O; Breazu, C; Mihailescu, IN; Iordache, I; Preda, N; Stanculescu, F

Published: OCT 2014, APPLIED PHYSICS A-MATERIALS SCIENCE & PROCESSING, 117, 268, DOI: 10.1007/s00339-014-8521-1

This paper presents some studies about the preparation by matrix-assisted pulsed laser evaporation (MAPLE) technique of organic bulk heterojunctions made from the mixture of a star-shaped arylenevinylene compound, 4,4',4aEuro(3)-tris[(4'-diphenylamino)styryl] triphenylamine as donor and fullerene derivative, [6, 6]-phenyl C61 butyric acid butyl ester, as acceptor, in the weight ratio 1:2. The mixed layer has been characterized by spectroscopic (UV-Vis, Fourier transform infrared) and microscopic (AFM) methods, and the effects of the deposition conditions (number of pulses) and of a buffer layer of poly(aniline-co-aniline propane sulfonic acid) or poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) have been analyzed. The study of the electrical properties has revealed a typical solar cell behavior for the heterostructure glass/ITO/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/4,4',4aEuro(3)-tris[(4'-diphenylamino)styryl] triphenylamine: [6, 6]-phenyl C61 butyric acid butyl ester/Al, confirming that MAPLE could be an adequate method for the preparation of active layer based on bulk heterojunction for solar cells.

470. Mechanisms of pulmonary toxicity developed at low and high doses of dextran-coated magnetite nanoparticles

Authors: Radu, M; Gheorghiu, A; Predoi, D; Hermenean, A; Ardelean, A; Dinischiotu, A

Published: SEP 10 2014, TOXICOLOGY LETTERS, 229, S78, DOI: 10.1016/j.toxlet.2014.06.301