National Institute Of Materials Physics - Romania

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5714 articles found

2431. Investigations of the non-isothermal crystallization of Bi4Ge3O12 (2:3) glasses

Authors: Aldica, G; Polosan, S

Published: MAY 1 2012, JOURNAL OF NON-CRYSTALLINE SOLIDS, 358, 1227, DOI: 10.1016/j.jnoncrysol.2012.02.025

Amorphous Bi4Ge3O12 glass samples were produced by melt quenching procedure stating with Bi4Ge3O12 (BGO) powder, obtained by solid state reaction between oxides. The kinetics of non-isothermal crystallization of EGO nano-crystals has been investigated. Differential Thermal Analysis (DTA) can give the main parameters of crystallization with an exothermic peak from 813 K to 851 K depending on the heating rate, which was assigned to the crystallization of cubic BGO in the amorphous matrix and compared with the X-Ray Diffraction (XRD) patterns. The nano-crystal dimensions were calculated from the XRD patterns by using the Debye-Scherrer method and were compared with Transmission Electron Microscopy (TEM) images. It was shown that the Ozawa model is most suitable for describing the behavior of non-isothermal crystallization of EGO nano-crystals within the glass matrix. Experimental results suggest a disk-shape type growth mechanism for the Bi4Ge3O12 nano-crystallites. The Flynn-Wall-Ozawa method has shown that the average activated energy value is 385 +/- 14 kJ/mol which was computed within the same model and agrees very well with the activation energy of the crystallization. (C) 2012 Elsevier B.V. All rights reserved.

2432. Catalyst size limitation in vapor-liquid-solid ZnO nanowire growth using pulsed laser deposition

Authors: Marcu, A; Trupina, L; Zamani, R; Arbiol, J; Grigoriu, C; Morante, JR

Published: MAY 1 2012, THIN SOLID FILMS, 520, 4631, DOI: 10.1016/j.tsf.2011.10.126

Using a pulsed laser deposition system in a plane reflector configuration, we have grown single crystal ZnO nanowires using different gold catalyst quantities and different local particle fluxes. The number of ZnO nanowire over the square micrometer substrate surface proved to depend on both gold quantity and particle flux, in specific conditions. If for a "low particle flux" the nanowire density seems to strongly depend on the gold quantity, for a "high particle flux", the dependence is no longer observable. The results were interpreted in terms of the catalyst absorbed particle concentration dependence on the catalyst droplet size and incident particle flux. (C) 2011 Elsevier B.V. All rights reserved.

2433. Optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films

Authors: Galca, AC; Socol, G; Craciun, V

Published: MAY 1 2012, THIN SOLID FILMS, 520, 4725, DOI: 10.1016/j.tsf.2011.10.194

The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In + Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In2O3), and counterbalance therefore the weak light absorption. (C) 2011 Elsevier B.V. All rights reserved.

2434. Noniterative method for evaluation of the complex material constants of piezoelectric ceramics in the radial vibration mode

Authors: Amarande, L

Published: MAY 2012, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 32, 1104, DOI: 10.1016/j.jeurceramsoc.2011.11.026

A new noniterative method, for determining the dielectric, piezoelectric and elastic constants, in complex form, for piezoceramic materials, in the radial mode, was proposed. This method uses the standard procedure to determine the elastic compliance and Poisson factor and the measurement of admittance at two frequencies to calculate the dielectric and piezoelectric constants, by solving a system of two equations. The accuracy of the new method was determined for materials with different planar coupling coefficients (k(p) = 2.5-57%) and mechanical quality factors (Q(m) = 20-3000). This method proved to be very accurate for all materials especially for those with large coupling factors. The accuracy of standard method was also evaluated for the same materials. (C) 2011 Elsevier Ltd. All rights reserved.

2435. Simultaneous dual-wavelength operation at 1.06 and 1.34 mu m in Nd-vanadate laser crystals

Authors: Salamu, G; Osiac, E; Dascalu, C; Pavel, N; Dascalu, T

Published: MAY 2012, LASER PHYSICS, 22, 871, DOI: 10.1134/S1054660X12050222

Output performances of Nd-vanadate lasers with simultaneous dual-wavelength emission on the 1.06-mu m (4) (3/2) -> (4) (11/2) transition and the (4) (3/2) -> (4) (13/2) transition at 1.34 mu m are discussed. The design uses a linear resonator for emission at 1.06 mu m and an L-type folded resonator for the 1.34-mu m wavelength, and the ratio between the power of a single wavelength and the total power is adjusted by the choice of the output mirror transmissions. A continuous-wave (CW) Nd:GdVO4 laser with total output power in the range of 3.9 to 6.8 W and the corresponding ratio of the output power at 1.06 mu m to the total output power between 0.26 and 0.97 is realized. It is also shown that in comparison with the pump at 808 nm, the pump directly into the (4) (3/2) emitting level at 879 nm improves the total output power. Furthermore, a Nd:GdVO4 laser with simultaneous emission at 1.06 and 1.34 mu m and that generates also green light at 0.53 mu m by intracavity frequency-doubling with LiB3O5 (LBO) nonlinear crystal is demonstrated.

2436. Study of radiation damage induced by 12 keV X-rays in MOS structures built on high-resistivity n-type silicon

Authors: Zhang, JG; Pintilie, I; Fretwurst, E; Klanner, R; Perrey, H; Schwandt, J

Published: MAY 2012, JOURNAL OF SYNCHROTRON RADIATION, 19, 346, DOI: 10.1107/S0909049512002348

Imaging experiments at the European X-ray Free Electron Laser (XFEL) require silicon pixel sensors with extraordinary performance specifications: doses of up to 1 GGy of 12 keV photons, up to 105 12 keV photons per 200 mu m X 200 mu m pixel arriving within less than 100 fs, and a time interval between XFEL pulses of 220 ns. To address these challenges, in particular the question of radiation damage, the properties of the SiO2 layer and of the SiSiO2 interface, using MOS (metal-oxide-semiconductor) capacitors manufactured on high-resistivity n-type silicon irradiated to X-ray doses between 10 kGy and 1 GGy, have been studied. Measurements of capacitance/conductancevoltage (C/GV) at different frequencies, as well as of thermal dielectric relaxation current (TDRC), have been performed. The data can be described by a dose-dependent oxide charge density and three dominant radiation-induced interface states with Gaussian-like energy distributions in the silicon band gap. It is found that the densities of the fixed oxide charges and of the three interface states increase up to dose values of approximately 10 MGy and then saturate or even decrease. The shapes and the frequency dependences of the C/GV measurements can be quantitatively described by a simple model using the parameters extracted from the TDRC measurements.

2437. One-Pot Hydroacetylation of Menadione (Vitamin K3) to Menadiol Diacetate (Vitamin K4) by Heterogeneous Catalysis

Authors: Dobrinescu, C; Iorgulescu, EE; Mihailciuc, C; Macovei, D; Wuttke, S; Kemnitz, E; Parvulescu, VI; Coman, SM

Published: MAY 2012, ADVANCED SYNTHESIS & CATALYSIS, 354, 1306, DOI: 10.1002/adsc.201100718

Vitamin K4 (menadiol diacetate, MDD) can be easily synthesized through cleaner and more efficient catalytic alternatives following the green chemistry principles. Ionic gold-based hydroxylated fluorides are active bi-functional catalysts for the one-pot hydroacetylation of menadione leading to MDD with 77% selectivity. Unprecedent results were obtained in the presence of oxide-fluoride catalysts by using a microwave-assisted hydrogen-transfer (MeerweinPonndorfVerley reaction) coupled with an acetylation approach, yielding very high selectivities for the target product (95%).

2438. Raman scattering and anti-Stokes luminescence in poly-paraphenylene vinylene/carbon nanotubes composites

Authors: Baibarac, M; Massuyeau, F; Wery, J; Baltog, I; Lefrant, S

Published: APR 15 2012, JOURNAL OF APPLIED PHYSICS, 111, DOI: 10.1063/1.4705403

In this paper, we present Raman scattering and luminescence of poly-paraphenylene vinylene/single-walled carbon nanotubes composites, focused on data recorded in the anti-Stokes branch. We demonstrate that, when the excitation energy is in the long wavelength tail of the fundamental absorption edge, an anti-Stokes signal is generated, whose origin is a photon absorption accompanied by a phonon process from lower to upper vibronic states. The efficiency of this anti-Stokes photo-luminescence is increased when composites films are deposited onto an Au rough surface acting as a surface enhanced Raman scattering substrate. This mechanism is explained by a coherent anti-Stokes Raman scattering-like process, as observed in other nano-structured materials. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4705403]

2439. AFM studies of metallic and organic nanosized structures ion beam sputtered onto functionalised surfaces

Authors: Crisan, AD; Crisan, O

Published: APR 2012, MATERIALS SCIENCE AND TECHNOLOGY, 28, 466, DOI: 10.1179/1743284711Y.0000000083

The growth of submonolayer metallic or molecular nanostructures via ion beam sputtering onto reconstructed semiconductor surfaces followed by in situ scanning probe imaging of the formed nanostructures provides an interesting basis for future development of new molecular multifunctional nanoarchitectured materials for various applications. The observed growth modes, structure and topology of pentacene, which is one of the most important candidates in the field of organic thin film electronic molecules, and Au metallic nanostructures deposited in the submonolayer regime onto reconstructed InP (0 0 1) surface, are discussed. During the initial stages of growth, a uniaxial diffusion channel dominates, and long pentacene molecular chains self-organise parallel to the [110] crystallographic direction on the InP surface. The study is performed by in situ non-contact atomic force microscopy (AFM) investigations with atomic resolution. It is shown that self-assembling of molecular structures onto flat terraces is dependent on the flatness and orientation of the terraces reconstructed onto the semiconductor surface. Moreover, it is possible to create functional molecular nanoarchitectures by nanomanipulation of single molecules with the AFM tip. This procedure may have large impact for technological applications such as organic thin film transistors and molecular nanowires.

2440. MgB2 with addition of Sb2O3 obtained by spark plasma sintering technique

Authors: Burdusel, M; Aldica, G; Popa, S; Enculescu, M; Badica, P

Published: APR 2012, JOURNAL OF MATERIALS SCIENCE, 47, 3836, DOI: 10.1007/s10853-011-6238-5

Superconducting bulks of MgB2 with addition of Sb2O3 and Sb with different stoichiometric compositions ((MgB2) + (Sb2O3) (x) , x = 0.0025, 0.005, 0.015, and (MgB2) + (Sb)(y), y = 0.01) were obtained by the Spark Plasma Sintering (SPS) technique. All added samples have high density, above 95% and critical temperature, T (c), of 38.1-38.6 K. This result and XRD data suggest that Sb does not enter the lattice of MgB2. Impurity phases are Mg3Sb2, MgO, and MgB4. The optimum addition is Sb2O3 for x = 0.005. This sample shows the critical current density, J (c)(5 K, 0 T) = 4 x 10(5) A/cm(2) and J (c)(5 K, 7 T) = 6 x 10(2) A/cm(2), while the irreversibility field, H (irr) (5 K, 100 A/cm(2)) = 8.23 T. Indicated values of J (c) and H (irr) are higher than for the pristine sample. The mechanism of J (c) and H (irr) increase in the Sb2O3 added samples is complex and composed of opposite effects most probably involving morphology elements, the presence of nano metric MgB4 and the indirect influence of oxygen or oxygen and Sb. Crystallite size of MgB2 is decreasing when Sb-based additions are introduced and the effect is stronger for the Sb-metal addition. The sample with Sb-metal addition does not improve J (c) and H (irr) when compared with pristine sample.