National Institute Of Materials Physics - Romania

Publications

5714 articles found

2771. Metal oxide nanoparticles synthesized by pulsed laser ablation for proton exchange membrane fuel cells

Authors: Dorcioman, G; Ebrasu, D; Enculescu, I; Serban, N; Axente, E; Sima, F; Ristoscu, C; Mihailescu, IN

Published: DEC 1 2010, JOURNAL OF POWER SOURCES, 195, 7780, DOI: 10.1016/j.jpowsour.2009.09.060

We report on the development of a modified gas diffusion layer for fuel cells consisting of a simple or teflonized carbon cloth pulsed laser deposited with metal oxide nanostructures designed to operate both as co-catalyst, and oxidic support for other electrochemically active catalysts. We selected TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO which were uniformly distributed over the surface of gas diffusion layers in order to improve the catalytic activity, stability and lifetime, and reduce the production costs of proton exchange membrane fuel cells. We evidenced by scanning electron microscopy and energy dispersive spectroscopy that our depositions consisted of TiO2 nanoparticles while in the case of ZnO and Al2O3 doped (2 wt.%) ZnO transparent quasi-continuous films were synthesized. (C) 2009 Elsevier BM. All rights reserved.

2772. Growth and characterization of Y0.7Sc0.3Ca4O(BO3)(3) single crystal for nonlinear optical applications

Authors: Achim, A; Gheorghe, L; Georgescu, S; Voicu, F

Published: DEC 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1980, DOI:

The nonlinear optical (NLO) crystal Y0.7Sc0.3Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been determined to be a = 0.80601(5) nm, b = 1.59946(8) nm, c = 0.35210(7) nm and beta = 101.165(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

2773. Topology of two-band superconductors

Authors: Tanaka, Y; Iyo, A; Tokiwa, K; Watanabe, T; Crisan, A; Sundaresan, A; Terada, N

Published: DEC 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, S967, DOI: 10.1016/j.physc.2009.10.036

Two-band superconductivity has a topology different from that in single-band superconductivity. The topology is not always stabilized in an infinitely homogeneous sample. The morphology, grain shape, and pattern of the device (topology of the superconducting materials) is effective in stabilizing the topology. In this report, we discuss a vortex having a small magnetic flux but a large winding number as one plausible topology in a two-band superconductor. (C) 2009 Elsevier B.V. All rights reserved.

2774. Barium magnesium tantalate thin films deposited by RF-magnetron sputtering from a stoichiometric target

Authors: Braic, V; Kiss, A; Ioachim, A; Toacsan, M; Nedelcu, L; Braic, M

Published: DEC 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 2385, DOI:

Barium magnesium tantalate thin films are attractive materials for high-performance dielectric ceramics for microwave devices, exhibiting a high dielectric constant, a low loss and a near-zero temperature coefficient. We report on the successful deposition of polycrystalline barium magnesium tantalate thin films by RF magnetron sputtering method. The structural and morphological characterization data are presented.

2775. Physico-chemical Properties of Iron-oxide-dextrin Thin Films

Authors: Ciobanu, CS; Andronescu, E; Pall, L; Iconaru, SL; Gyorgy, E; Predoi, D

Published: DEC 2010, REVISTA DE CHIMIE, 61, 1211, DOI:

Iron oxide nanoparticles were synthesized in the presence of dextrin. The adsorption process of different dextrin molecules onto the surface of in water dispersed iron-oxide nanoparticles has been investigated to optimize the preparation of iron oxide magnetic fluids. An average iron oxide core size of 8 nm was found by transmission electron microscopy (TEM) for the samples. Scanning electron microscopy (SEM) micro-structural studies revealed a spherical shape of the particles. X-ray phase analysis revealed spinel structure of the iron oxide particles. The attachment of the dextrin on the particle surface was investigated by FTIR spectrometry. The dextrin coated iron oxide nanoparticles were used as targets in Pulsed Laser Deposition (PLD) experiments for thin films synthesis.

2776. Integrated nanotechnology of pinning centers in YBa2Cu3Ox films

Authors: Mikheenko, P; Dang, VS; Tse, YY; Kechik, MMA; Paturi, P; Huhtinen, H; Wang, Y; Sarkar, A; Abell, JS; Crisan, A

Published: DEC 2010, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 23, DOI: 10.1088/0953-2048/23/12/125007

A controlled pinning change from the ab-plane dominant to the c-axis dominant has been achieved in a novel method of nanostructured YBa2Cu3Ox (YBCO) growth. The method is a synchronous self-assembly of BaZrO3 (BZO) and Ag-assisted YBCO nanothreads. The formation of entangled nanothreads increases the critical current density while keeping the critical temperature close to that in pure YBCO films. The nanothreads extend through the whole thickness of thick films, making the method suitable for increasing total critical current density per centimeter of width (Ic-w). Two growth mechanisms, the formation of BZO nanorods and YBCO nanocolumns, complement each other, form a coherent structure and produce samples with strong correlated pinning. In addition to the increase in Ic-w, correlated pinning leads to an increase in vortex melting temperature in a wide range of magnetic fields. The films grown by this method have high Ic-w both in low magnetic fields along the c axis and high magnetic fields in the ab plane of YBCO. Such a superconductor would be suitable for both cable and magnet applications.

2777. Nanodots induced columnar growth of YBa2Cu3Ox films

Authors: Mikheenko, P; Tanner, JL; Bowen, J; Sarkar, A; Dang, VS; Abell, JS; Crisan, A

Published: DEC 2010, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 470, S236, DOI: 10.1016/j.physc.2009.11.064

We report columnar growth of YBa2Cu3Ox (YBCO) films by pulsed laser deposition using nanodots of Au, Ag and Pd deposited on SrTiO3 substrate prior to the growth of the film. The nanodots initiate formation of densely packed YBCO columns with c-axis along the length of the columns. The obtained columnar structure offers enhanced pinning of magnetic flux and provides high critical current density in a magnetic field directed along the c-axis of YBCO while keeping high critical current density for other directions of magnetic field. The evidence of columnar structure is given by the planar and cross-sectional atomic force microscopy, transmissional election microscopy and rotational transport measurements of critical current. By creating the columnar structure, an improvement of critical current up to about 200% is achieved comparable to the reference samples without nanodots in a wide range of magnetic field and thickness of the samples. The largest increase in critical current is observed in magnetic fields close to the matching field calculated from the density of nanoparticles or density of YBCO columns. (C) 2009 Elsevier BM. All rights reserved.

2778. Novel Pd heterogeneous catalysts for cycloisomerisation of acetylenic carboxylic acids

Authors: Neatu, F; Protesescu, L; Florea, M; Parvulescu, VI; Teodorescu, CM; Apostol, N; Toullec, PY; Michelet, V

Published: DEC 2010, GREEN CHEMISTRY, 12, 2149, DOI: 10.1039/c0gc00258e

The Pd-TPPTS complex (TPPTS - trisodium salt of 3,3',3 ''-phosphanetriyl benzenesulfonic acid) and PdCl42- salt heterogenised onto Zn2AlNO3 layered double hydroxide (LDH) using an ion-exchange procedure, have been shown to be efficient green catalysts in the cycloisomerisation reaction of acetylenic carboxylic acids to the corresponding 5-membered heterocycles.

2779. Effect of the morphology on the optical and electrical properties of TPyP thin films deposited by vacuum evaporation

Authors: Socol, M; Rasoga, O; Stanculescu, F; Girtan, M; Stanculescu, A

Published: DEC 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 2038, DOI:

We have studied the effect of the morphology on the optical and electrical properties of the TPyP thin films deposited by vacuum evaporation on different substrates (Si with different characteristics, ITO, quartz and glass). The presence of some well-defined B and Q absorption bands has been evidenced. FTIR and photoluminescence measurements have been used to confirm the preservation of the chemical structure of the compound during the evaporation process. The contact Au/TPyP/Si(n) is rectifier, while a blocking behavior has been shown by Si(n)/TPyP/Si(n) and ITO/TPyP/Si(n) and an injector dominated behavior by Si(p)/TPyP/Si(p) and ITO/TPyP/Si(p) heterostructures. The best transmission was obtained on TPyP film deposited on ITO and the highest value of the current in heterostructures Si(n) electrode characterised by a large grain morphology and in consequence by a weak optical and charge carrier scattering at the grain boundaries.

2780. Crystal growth, NCPM second harmonic generation, and infrared laser performance for SFD in Gd1-x-yRxNdyCa4O(BO3)(3) (R = Sc or Lu) crystals

Authors: Gheorghe, L; Aka, G

Published: DEC 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1976, DOI:

Nonlinear optical borate crystals of Gd1-x-yRxNdyCa4O(BO3)(3) crystals with large size and good quality have been grown from the melt by the Czochralski pulling method. The chemical compositions of the grown crystals were determined and nonlinear optical properties of these new biaxial crystals are reported. According to our assumptions, the obtained results demonstrate that the grown crystals convert the near infrared radiation of similar to 936 nm into blue light (similar to 468 nm) by type-I noncritical phase matching (NCPM) second harmonic generation (SHG) processes along Z axis. Preliminary investigations of self frequency doubling (SFD) processes in Gd1-x-yRxNdyCa4O(BO3)(3) crystals have been carried out.