National Institute Of Materials Physics - Romania

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5781 articles found

1511. Synthesis and characterization of PLD glass phosphate films doped with CdS

Authors: Elisa, M; Iordanescu, CR; Vasiliu, IC; Feraru, ID; Epurescu, G; Filipescu, M; Plapcianu, C; Bartha, C; Trusca, R; Peretz, S

Published: MAR 2017, JOURNAL OF MATERIALS SCIENCE, 52, 2901, DOI: 10.1007/s10853-016-0583-3

In the present work, optical, structural and morphological properties of CdS-doped phosphate films obtained by pulsed laser deposition (PLD) method were investigated. In the deposition process, a target based on a mixture composed of Li2O-Al2O3-BaO-La2O3-ZnO-P2O5 glass and CdS powder as dopant was used. The phosphate glass target was obtained by non-conventional wet route of raw reagents processing followed by melt-quenching technique. The complex oxide composition of the glass as well as the final PLD target consisting in a mixture of glass and CdS powder followed by pressing and heat treatment represents the novelty of the work. CdS dopant particles were highlighted by X-ray diffraction analysis as well as by Raman spectroscopy. Thus, cubic CdS particles having less than 10 nm size corroborated with specific LO (longitudinal optical phonons) and 2LO CdS Raman peaks from 300 and 600 cm(-1), respectively, certified the presence of the dopant in the deposited films. Specific vibration modes for the vitreous phosphate matrix were revealed by fourier transform infrared spectroscopy, and spherulitic units characteristic to PLD technique were found by scanning electron microscopy and atomic force microscopy analyses. A relative large luminescence band located around 430 nm was provided by UV excitation, representative for CdS nanoparticles having about 9-10 nm size.

1512. Electrochemical characterization of the Poly(2, 2 '-Bithiophene-co-Pyrene) Functionalized Single-Walled Carbon Nanotubes Films and Their Applications in Supercapacitors Field

Authors: Baibarac, M; Baltog, I; Daescu, M

Published: MAR 2017, INTERNATIONAL JOURNAL OF ELECTROCHEMICAL SCIENCE, 12, 2025, DOI: 10.20964/2017.03.60

The performance of the poly(2, 2'-bithiophene-co-pyrene) copolymer doped with bis(2-ethyl hexyl) sulfosuccinate sodium (AOT) anions [(PBTh-Py)(+)AOT(-)] and its composite with single-walled carbon nanotubes (SWNTs) [(PBTh-Py)(+)AOT(-)/SWNTs] as active materials for the electrodes of symmetrical supercapacitors is demonstrated in this work. Using cyclic voltammetry, the influence of the electrolyte concentration and the different cations on the oxidation and reduction processes at the electrolyte/electrode interface is reported. Using charge-discharge galvanostatic measurements in the case of the symmetrical-supercapacitors having as electrode active materials, the (PBTh-Py)(+)AOT(-) copolymer and the (PBTh-Py)(+)AOT(-)/SWNTs composite, values of the specific capacitance equal with 11.5 and 59 F g(-1), respectively, for current densities of 100 mA g(-1), were reported.

1513. Mn2+ ions distribution in doped sol-gel deposited ZnO films

Authors: Stefan, M; Ghica, D; Nistor, SV; Maraloiu, AV; Plugaru, R

Published: FEB 28 2017, APPLIED SURFACE SCIENCE, 396, 1889, DOI: 10.1016/j.apsusc.2016.02.167

The localization and distribution of the Mn2+ ions in two sol-gel deposited ZnO films doped with different manganese concentrations were investigated by electron paramagnetic resonance spectroscopy and analytical transmission electron microscopy. In the lightly doped sample the Mn2+ ions are mainly localized substitutionally at isolated tetrahedrally coordinated Zn2+ sites in both crystalline ZnO nanograins (34%) and surrounding disordered ZnO (52%). In the highly doped ZnO film, a much smaller proportion of manganese substitutes Zn2+ in the crystalline and disordered ZnO (10%). The main amount (85%) of manganese aggregates in a secondary phase as an insular-like distribution between the ZnO nanograins. The remaining Mn2+ ions (14% and 5% at low and high doping levels, respectively) are localized at isolated, six-fold coordinated sites, very likely in the disordered intergrain region. Annealing at 600 degrees C induced changes in the Mn2+ ions distribution, reflecting the increase of the ZnO crystallization degree, better observed in the lightly doped sample. (C) 2016 Elsevier B.V. All rights reserved.

1514. Short-wave infrared LEDs from GeSn/SiGeSn multiple quantum wells

Authors: Stange, D; den Driesch, NV; Rainko, D; Roesgaard, S; Povstugar, I; Hartmann, JM; Stoica, T; Ikonic, Z; Mantl, S; Grutzmacher, D; Buca, D

Published: FEB 20 2017, OPTICA, 4, 188, DOI: 10.1364/OPTICA.4.000185

Group IV photonics is on its way to be integrated with electronic circuits, making information transfer and processing faster and more energy efficient. Light sources, a critical component of photonic integrated circuits, are still in development. Here, we compare multi-quantum-well (MQW) light-emitting diodes (LEDs) with Ge0.915Sn0.085 wells and Si0.1Ge0.8Sn0.1 barriers to a reference Ge0.915Sn0.085 homo-junction LED. Material properties as well as band structure calculations are discussed, followed by optical investigations. Electroluminescence spectra acquired at various temperatures indicate effective carrier confinement for electrons and holes in the GeSn quantum wells and confirm the excellent performance of GeSn/SiGeSn MQW light emitters. (C) 2017 Optical Society of America

1515. Nano-engineered pinning centres in YBCO superconducting films

Authors: Crisan, A; Dang, VS; Mikheenko, P

Published: FEB 15 2017, PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 533, 132, DOI: 10.1016/j.physc.2016.06.011

For practical applications of superconducting materials in applied magnetic fields, artificial pinning centres in addition to natural ones are required to oppose the Lorentz force. These pinning centres are actually various types of defects in the superconductor matrix. The pinning centres can be categorised on their dimension (volume, surface or point) and on their character (normal cores or AK cores). Different samples have been produced by Pulsed Laser Deposition, with various thicknesses, temperatures and nanostructured additions to the superconducting matrix. They have been characterized by SQUID Magnetic Properties Measurement System and Physical Properties Measurement System, as well as by Transmission Electron Microscopy (TEM). Correlations between pinning architecture, TEM images, and critical currents at various fields and field orientations will be shown for a large number of YBa2Cu3Ox films with various types and architectures of artificial pinning centres. (C) 2016 Elsevier B.V. All rights reserved.

1516. Magnetite-based glass-ceramics prepared by controlled crystallization of borosilicate glasses: Effect of nucleating agents on magnetic properties and relaxation

Authors: Sandu, V; Cimpoiasu, E; Greculeasa, S; Kuncser, A; Nicolescu, MS; Kuncser, V

Published: FEB 15 2017, CERAMICS INTERNATIONAL, 43, 3413, DOI: 10.1016/j.ceramint.2016.11.188

The specific magnetic structure and magnetic relaxation phenomena in magnetite nanoentities grown in a glassy matrix by controlled crystallization of Fe-containing borosilicate and boroaluminosilicate glasses in the presence of two types of nucleating agents, Cr2O3 and P2O5, were investigated. The structure, morphology and magnetic properties are strongly influenced by the nucleating agents. Cr2O3 generates magnetite-based glass ceramics with magnetite configurations showing an upward relaxation of magnetization at low and high temperatures but downward at intermediate temperatures. The magnetite grown with P2O5 displays only downward relaxation but with different signs of the temperature derivative of the relaxation rate S in different temperature ranges. The observed effects are discussed with respect to the following factors: i) the existence of a multimodal size distribution of the magnetite (nano)particles as revealed by high resolution electron microscopy; ii) the degree of occupation of different sublattices of the magnetite structure with Fe3+ and Fe2+ ions; and the interplay between the relaxation mechanisms in different temperature ranges.

1517. Optical properties of single-walled carbon nanotubes highly separated in semiconducting and metallic tubes functionalized with poly(vinylidene fluoride)

Authors: Matea, A; Baibarac, M; Baltog, I

Published: FEB 15 2017, JOURNAL OF MOLECULAR STRUCTURE, 1130, 45, DOI: 10.1016/j.molstruc.2016.10.017

In this paper, the interaction of poly(vinylidene fluoride) (PVDF) with single-walled carbon nanotubes (SWNTs) highly separated in metallic (M) and semiconducting (S) tubes is studied by resonant Raman scattering and FTIR spectroscopy. In this order, the PVDF/SWNTs membranes were prepared by the evaporation of dimethylformamide (DMF) from PVDF solutions containing i) the as-prepared SWNTs samples, i.e., as mixtures of metallic (33%) and semiconducting (66%) tubes (M + S-SWNTs), ii) SWNTs highly separated in metallic tubes (98%, M-SWNTs), and iii) SWNTs highly separated in semiconducting tubes (99%, S-SWNTs). An increase in the PVDF beta phase weight, highlighted by the increase in the absorbance of IR band at 843 cm(-1), is reported to take place in the presence of M + S-SWNTs and S-SWNTs. An increase of the PVDF gamma crystalline phase weight is reported for the PVDF/M + S-SWNTs, PVDF/M-SWNTs and PVDF/S-SWNTs membranes. Using Raman scattering, a donor-acceptor interaction is invoked to take place at the interface PVDF/M + S-SWNTs and PVDF/S-SWNTs. In the case of the membranes based on PVDF and M-SWNTs, the changes reported in Raman spectra of the two constituents are explained on the base induction-interaction forces between the permanent dipole of PVDF and induced dipole of M-SWNTs. (C) 2016 Elsevier B.V. All rights reserved.

1518. On the threshold for ion track formation in CaF2

Authors: Karlusic, M; Ghica, C; Negrea, RF; Siketic, Z; Jaksic, M; Schleberger, M; Fazinic, S

Published: FEB 10 2017, NEW JOURNAL OF PHYSICS, 19, DOI: 10.1088/1367-2630/aa5914

There is an ongoing debate regarding the mechanism of swift heavy ion (SHI) track formation in CaF2. The objective of this study is to shed light on this important topic using a range of complementary experimental techniques. Evidence of the threshold for ion track formation being below 3 keV nm(-1) is provided by both transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy in the channelling mode, which has direct consequences for the validity of models describing the response of CaF2 to SHI irradiation. Furthermore, information about the elemental composition within the ion tracks is obtained using scanning TEM, electron energy loss spectroscopy, and with respect to the stoichiometry of the materials surface by in situ time of flight elastic recoil detection analysis. Advances in the analyses of the experimental data presented here pave the way for a better understanding of the ion track formation.

1519. Structure and magnetic properties of CoFe2O4/SiO2 nanocomposites obtained by sol-gel and post annealing pathways

Authors: Dippong, T; Cadar, O; Levei, EA; Bibicu, I; Diamandescu, L; Leostean, C; Lazar, M; Borodi, G; Tudoran, LB

Published: FEB 1 2017, CERAMICS INTERNATIONAL, 43, 2122, DOI: 10.1016/j.ceramint.2016.10.192

The influence of the CoFe2O4 nanoparticles concentration in silica matrix on the structural and magnetic properties of xCoFe(2)O(4)/(100-x)SiO2 nanocomposites with x=10, 30, 50, 70 and 90 was studied. Magnetic CoFe2O4 nanoparticles dispersed in silica matrix was obtained by sol-gel method, followed by annealing at 1100 degrees C. The X-ray diffraction pattern and FT-IR spectra revealed the single spinel ferrite structure for all samples. The FT-IR spectra also suggested the formation of the amorphous silica matrix. The results showed that the increase of cobalt ferrite concentration (x) in the silica matrix leads to high crystallinity, specific surface area and particle size. The magnetic CoFe2O4 nanoparticles have spherical shapes and size in the 6-35 nm range. The Mossbauer measurements were fitted with two Zeeman sextets, indicating that all the samples were completely magnetically ordered. The vibrating sample magnetometer studies showed that the saturation magnetization (Ms) and coercivity (Hc) of the CoFe2O4 nanocrystals embedded in silica matrix possessed a linear relationship with the mean crystallite size. Also, the saturation magnetization of the studied nanocomposites increases with the increase of cobalt ferrite concentration (x) in the silica matrix.

1520. A general perspective on the magnetization reversal in cylindrical soft magnetic nanowires with dominant shape anisotropy

Authors: Kuncser, A; Antohe, S; Kuncser, V

Published: FEB 1 2017, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 423, 38, DOI: 10.1016/j.jmmm.2016.09.066

Peculiarities of the magnetization reversal process in cylindrical Ni-Cu soft magnetic nanowires with dominant shape anisotropy are analyzed via both static and time dependent micromagnetic simulations. A reversible process involving acoherent-like spin rotation is always observed for magnetic fields applied perpendicularly to the easy axis whereas nucleation of domain walls is introduced for fields applied along the easy axis. Simple criteria for making distinction between a Stoner-Wohlfarth type rotation and a nucleation mechanism in systems with uniaxial magnetic anisotropy are discussed. Superposed reversal mechanisms can be in action for magnetic fields applied at arbitrary angles with respect to the easy axis within the condition of an enough strong axial component required by the nucleation. The dynamics of the domain wall, involving two different stages (nucleation and propagation), is discussed with respect to initial computing conditions and orientations of the magnetic field. A nucleation time of about 3 ns and corkscrew domain walls propagating with a constant velocity of about 150 m/s are obtained in case of Ni-Cu alloy (Ni rich side) NWs with diameters of 40 nm and high aspect ratio.