National Institute Of Materials Physics - Romania

Publications

5714 articles found

2041. Cladding waveguides realized in Nd:YAG ceramic by direct femtosecond-laser writing with a helical movement technique

Authors: Salamu, G; Jipa, F; Zamfirescu, M; Pavel, N

Published: APR 1 2014, OPTICAL MATERIALS EXPRESS, 4, 797, DOI: 10.1364/OME.4.000790

Circular cladding waveguides were realized in a 5.0-mm long, 1.1- at.% Nd:YAG ceramic by direct femtosecond-laser writing using a scheme in which the laser medium is moved on a helical trajectory along its axis and parallel to the writing direction. Laser emission was obtained under the pump with a fiber-coupled diode laser. A 100-mu m diameter waveguide delivered laser pulses at 1.06 mu m with 3.4-mJ energy for the pump with pulses of 13.1-mJ energy, at 0.30 slope efficiency; laser pulses at 1.3 mu m with 1.2-mJ energy were obtained from the same device. Comparison with a waveguide of the same dimension that was inscribed by the classical translation method of the laser medium is made. Efficient integrated lasers based on cladding waveguides that are pumped by fiber-coupled diode lasers could be realized by this writing method. (C) 2014 Optical Society of America

2042. Improved laser efficiency by direct diode laser pumping of the radiation-resistant Nd:gadolinium-scandium-gallium garnet

Authors: Lupei, V; Pavel, N; Lupei, A

Published: APR 2014, LASER PHYSICS, 24, DOI: 10.1088/1054-660X/24/4/045801

Spectroscopic investigation of the radiation-resistant Nd:GSGG crystals and ceramics reported in this paper evidences that the absorption line at 883 nm corresponding to the unusual situation of quasi-degenerate absorption transitions I-4(9/2)(2) -> F-4(3/2)(1) and I-4(9/2)(3) -> F-4(3/2)(2) can be used for efficient direct diode laser pumping of this material, with stable absorption over an extended temperature range. It is inferred that the reduction of the quantum defect at this wavelength of pump compared to the traditional 807 nm pumping could improve the laser parameters and reduce drastically the heat generation, leading to a considerable extension of the power scalability. This possibility is demonstrated for the first time in the case of the 1061 nm laser emission in a continuous-wave and in the repetitive active acousto-optic and passive Q-switched laser emission. In all regimes this manifests in the reduction of the laser threshold, increase of slope efficiency and extension of the average power range. Additionally, in the active Q-switching this enables increased pulse energy and reduced pulse duration. The direct pumping could revitalize the utilization of Nd:GSGG for construction of lasers with storage of population inversion or working in an ionizing radiation environment.

2043. Tough and dense boron carbide obtained by high-pressure (300 MPa) and low-temperature (1600 degrees C) spark plasma sintering

Authors: Badica, P; Grasso, S; Borodianska, H; Xie, SS; Li, PF; Tatarko, P; Reece, MJ; Sakka, Y; Vasylkiv, O

Published: APR 2014, JOURNAL OF THE CERAMIC SOCIETY OF JAPAN, 122, 275, DOI: 10.2109/jcersj2.122.271

Dense boron carbide (above 95%) was achieved through high pressure (300 MPa) and low temperature (1600 degrees C) Spark Plasma Sintering (SPS). This approach resulted in improvement of fracture toughness and of dynamic toughness when compared to corresponding toughness values of the sample sintered by conventional SPS (2100 degrees C, 50 MPa). Dynamic toughness was extracted from Split Hopkinson Pressure Bar measurements. Results are understood based on microstructure and on very different behaviour of the samples in respect to residual B2O3 and carbon available in the raw B4C powder. (C) 2014 The Ceramic Society of Japan. All rights reserved.

2044. Thermal behavior of several stable hydrazyl free radicals and of their parent hydrazines

Authors: Marinescu, M; Zalaru, C; Florea, M; Ionita, P

Published: APR 2014, , DOI: 10.1007/s10973-013-3448-x

2045. Electric-field-induced transformations in epitaxial relaxor ferroelectric PbMg1/3Nb2/3O3 films

Authors: Tyunina, M; Pintilie, I; Iuga, A; Pintilie, L

Published: MAR 24 2014, PHYSICAL REVIEW B, 89, DOI: 10.1103/PhysRevB.89.094106

Electric-field-induced transformations are studied experimentally in cube-on-cube-type epitaxial film of relaxor ferroelectric (FE) PbMg1/3Nb2/3O3 grown on (001) MgO substrate. The dielectric response, polarization, and current are measured along the out-of-plane < 100 > direction of the film and analyzed as a function of temperature, frequency, and applied field. Compared to the < 100 > crystal, transformation of the low-temperature relaxor state to a new state in the (001) film takes place at considerably lower temperatures and larger fields. Based on the found bisigmoidal shape and the two scaling regimes of the current-voltage curves, the two corresponding electric-field-induced processes are suggested to be dipolar flips and flow of a phase boundary in the film. The field-induced state in the film is dynamic and unstable, and it differs from the field-induced FE state in the crystal. The robustness of the relaxor state to electric field in the film is discussed in relation to spatial anisotropy of the dipolar system in the (001) film.

2046. Magnetic nanoparticles in MgB2

Authors: Sandu, V; Chee, CY

Published: MAR 15 2014, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 498, 37, DOI: 10.1016/j.physc.2013.12.008

Additional pinning generated by magnetic nanoparticles which were created or inserted within polycrystalline MgB2 superconductor is analyzed. The composites were built in two ways: (i) ceramization of polysiloxane-co-ferrocene based copolymers and (ii) insertion of coated nanoparticles. The composites present two types of pinning: core pinning based on the variation of the superconducting parameter when a non-superconducting particle is present and a magnetic pinning resulting from the interaction of the screening currents around the particle and the flux line. All samples show a consistent improvement of the critical current density when the magnetic moment of the sample in normal state is finite but small, showing a maximum for a magnetic moment of 0.015 emu/cm(3). A tentative description of the effect of magnetic pinning is presented in the framework of the collective pinning. (C) 2014 Elsevier B.V. All rights reserved.

2047. Laser emission from diode-pumped Nd:YAG ceramic waveguide lasers realized by direct femtosecond-laser writing technique

Authors: Salamu, G; Jipa, F; Zamfirescu, M; Pavel, N

Published: MAR 10 2014, OPTICS EXPRESS, 22, 5182, DOI: 10.1364/OE.22.005177

We report on realization of buried waveguides in Nd: YAG ceramic media by direct femtosecond-laser writing technique and investigate the waveguides laser emission characteristics under the pump with fiber-coupled diode lasers. Laser pulses at 1.06 mu m with energy of 2.8 mJ for the pump with pulses of 13.1-mJ energy and continuous-wave output power of 0.49 W with overall optical efficiency of 0.13 were obtained from a 100-mu m diameter circular cladding waveguide realized in a 0.7-at.% Nd: YAG ceramic. A circular waveguide of 50-mu m diameter yielded laser pulses at 1.3 mu m with 1.2-mJ energy. (c) 2014 Optical Society of America

2048. Influence of film thickness on the morphological and electrical properties of epitaxial TiC films deposited by reactive magnetron sputtering on MgO substrates

Authors: Zoita, NC; Braic, V; Danila, M; Vlaicu, AM; Logofatu, C; Grigorescu, CEA; Braic, M

Published: MAR 1 2014, JOURNAL OF CRYSTAL GROWTH, 389, 98, DOI: 10.1016/j.jcrysgro.2013.11.076

Epitaxial TiC films were deposited on MgO (001) by DC magnetron sputtering in a reactive atmosphere of Ar and CH4 at 800 degrees C. The films elemental composition and chemical bonding was investigated by Auger electron spectroscopy (AE5), X-ray photoelectron spectroscopy (XPS) and micro-Raman spectroscopy. The crystallographic structure, investigated by X-ray diffraction, exhibited an increased degree of (001) orientation with the film thickness, with a cube-on-cube epitaxial relationship with the substrate. The films morphology and electrical properties were determined by atomic force microscopy (AFM) and Hall measurements in Van der Pauw geometry. The influences of the film thickness (57-545 nm) on the morphological and electrical properties were investigated. The thinnest film presented the lowest resistivity, 160 [152, cm, showing an atomically flat surface, while higher values were obtained for the thicker films, explained by their different morphology dominated by low aspect ratio nanoislands/ nanocolumns. (C) 2013 Elsevier B.V. All rights reserved

2049. Studies on thermal, spectral, magnetic and biological properties of new Ni(II), Cu(II) and Zn(II) complexes with a bismacrocyclic ligand bearing an aromatic linker

Authors: Bucur, C; Badea, M; Chifiriuc, MC; Bleotu, C; Iorgulescu, EE; Badea, IA; Grecu, MN; Lazar, V; Patriciu, OI; Marinescu, D; Olar, R

Published: MAR 2014, JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY, 115, 2189, DOI: 10.1007/s10973-013-3460-1

Novel complexes of M2LCl4 center dot nH(2)O type (M:Ni, n = 4; M:Cu, n = 3 and M:Zn, n = 0; L: ligand resulted from 1,4-phenylenediamine, 3,6-diazaoctane-1,8-diamine and formaldehyde one-pot condensation) were synthesized and characterised by microanalytical, ESI-MS, IR, UV-Vis, H-1 NMR and EPR spectra, magnetic data at room temperature and molar conductivities as well. The electrochemical behaviour of complexes was investigated by cyclic voltammetry. Simultaneous TG/DTA measurements were performed in order to evidence the thermal behaviour of the obtained complexes. Processes such as water elimination, fragmentation and oxidative degradation of the organic ligand as well as chloride elimination occurred during thermal decomposition. The antimicrobial assays demonstrate that the compounds exhibited good antibacterial activity, especially against S. aureus and E. coli strains, the most active being the copper(II) complex, which also exhibited the most prominent anti-biofilm effect, suggesting its potential use for the development of new antimicrobial agents. The biological activity was correlated with log P (ow) values. All complexes disrupt the membrane integrity of HCT 8 tumour cells.

2050. Toughness control of boron carbide obtained by spark plasma sintering in nitrogen atmosphere

Authors: Badica, P; Borodianska, H; Xie, SM; Zhao, T; Demirskyi, D; Li, PF; Tok, AIY; Sakka, Y; Vasylkiv, O

Published: MAR 2014, CERAMICS INTERNATIONAL, 40, 3061, DOI: 10.1016/j.ceramint.2013.09.141

Boron carbide ceramic was prepared by reactive Spark Plasma Sintering under N-2-atmosphere and for different heating times and maximum pressure regimes. Split-Hopkinson Pressure Bar (SHPB), indentation, XRD and microscopy measurements were performed for samples characterization. It is shown that SHPB toughness control depending on SPS regime is possible and the main reason is introduction of nitrogen into B4C ceramic. Complex relationships between processing conditions, sintering mechanism, material's specifics, static and dynamic mechanical properties are discussed. Improvement of dynamic toughness is through mechanisms resembling those working for static load conditions such as cracks deflection and pull out, but there are also significant differences. (c) 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.