National Institute Of Materials Physics - Romania

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5781 articles found

2501. 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.

2502. 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.

2503. 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.

2504. 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%).

2505. 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]

2506. 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.

2507. 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.

2508. Sol-gel template synthesis of luminescent glass-ceramic rods

Authors: Secu, M; Secu, CE; Sima, M

Published: APR 2012, JOURNAL OF NANOPARTICLE RESEARCH, 14, DOI: 10.1007/s11051-012-0772-1

We report an original way to prepare luminescent glass-ceramic microrods containing Eu3+ doped BaF2 nanocrystals by sol-gel chemistry within the pores of a polycarbonate template membrane. Structural characterization by scanning electron microscopy and X-ray diffraction has shown the formation of glass-ceramic microrods with 0.8-m diameter of and 10 mu m length in which BaF2 nanocrystals of about 30 nm size are embedded. Photoluminescence measurements have indicated the incorporation of Eu3+ ions inside the BaF2 nanocrystals in a broad range of sites with low coordination symmetry. The comparison made with the bulk glass-ceramic indicated an influence of the dimensional constraints imposed by the membrane pores during xerogel formation and subsequent glass ceramization.

2509. Spark-plasma-sintering temperature dependence of structural and piezoelectric properties of BNT-BT0.08 nanostructured ceramics

Authors: Cernea, M; Fochi, F; Aldica, GV; Vasile, BS; Trusca, R; Galassi, C

Published: APR 2012, JOURNAL OF MATERIALS SCIENCE, 47, 3673, DOI: 10.1007/s10853-011-6215-z

(Bi0.5Na0.5)TiO3 doped with 8 mol% BaTiO3 powder prepared by sol-gel was compacted and sintered by spark-plasma-sintering method. The influence of spark-plasma-sintering temperature on the densification and piezoelectric properties of these ceramics was studied. Starting from BNT-BT0.08 powder gel with a microstructure consisting of particles with average size of 50 nm, ceramics with grain size of 60-90 nm and density of about 98.9-99.6% of the theoretical density were obtained by spark-plasma-sintering at 800-900 A degrees C. Increasing the sintering temperature by SPS from 800 to 900 A degrees C lead to the increase of d (33), k (p), epsilon (33) (T) and, decrease of Q (m). Typical d (33) and k (p) values of BNT-BT0.08 ceramics sintered by spark-plasma-sintering at 900 A degrees C were 8 and 0.029, respectively.

2510. Photoluminescence and magnetic circular dichroism of IrQ(ppy)(2)-5Cl

Authors: Polosan, S; Radu, IC; Tsuboi, T

Published: APR 2012, JOURNAL OF LUMINESCENCE, 132, 1002, DOI: 10.1016/j.jlumin.2011.12.002

Photoluminescence and magnetic circular dichroism of the IrQ(ppy)(2)-5Cl compound were investigated between 15 and 295 K. These results have been compared with the output files obtained from Density Functional Theory by using the Gaussian 03W software and some additional packages. The experimental results confirm the first triplet state absorption which arises from d to pi(Q) transition. The temperature dependence photoluminescence have shown a small interaction with the polystyrene, used for dispersion of IrQ(ppy)(2)-5Cl compound. The green and red phosphorescence have the same temperature dependence. The MCD spectra, especially at 15K, reveals the main transitions involved in the Metal-to-Ligand Charge Transfer processes from the Ir towards the two ligands, phenylpyridine and quinoline, respectively. (C) 2011 Elsevier B.V. All rights reserved.