National Institute Of Materials Physics - Romania

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873 articles found

501. Organic heterostructures based on arylenevinylene oligomers deposited by MAPLE

Authors: Socol, M; Preda, N; Vacareanu, L; Grigoras, M; Socol, G; Mihailescu, N; Stanculescu, F; Jelinek, M; Stanculescu, A; Stoicanescu, M

Published: MAY 30 2014, APPLIED SURFACE SCIENCE, 302, 222, DOI: 10.1016/j.apsusc.2013.12.091

Organic heterostructures were fabricated by matrix assisted pulsed laser evaporation (MAPLE) method using arylenevinylene oligomers based on triphenylamine (P78)/carbazole (P13) group and tris(8-hydroxyquinolinato)aluminum salt (Alq3). Optical properties of the organic multilayer structures were characterized by spectroscopic techniques: FTIR, UV-vis and photoluminescence (PL). A good transparency (over 60%) was remarked for the structures with two organic layers in the 550-800 nm range. Photoluminescence (PL) spectra proved that the emission characteristics of the materials have been preserved. I-V characteristics of (ITO/oligomer/Alq3/Al and ITO/Alq3/Al) heterostructures were symmetrically while rectifying properties of these heterostructures have not been observed. A comparison between the heterostructures made of layers with different thickness reveals that the higher current (8 x 10(-6) A at 1 V) was obtained for the ITO/P78/Alq3/Al heterostructure, which is characterized by a larger thickness of the double organic layer. AFM measurements revealed a similar topography while RMS values of the reported structures depend on the organic material. (C) 2013 Elsevier B.V. All rights reserved.

502. Laser prepared organic heterostuctures on glass/AZO substrates

Authors: Stanculescu, A; Socol, M; Rasoga, O; Mihailescu, IN; Socol, G; Preda, N; Breazu, C; Stanculescu, F

Published: MAY 30 2014, APPLIED SURFACE SCIENCE, 302, 176, DOI: 10.1016/j.apsusc.2014.01.181

This paper presents some studies about the bi-layer organic heterostructures realized with zinc phthalocyanine (ZnPc) as donor layer and 1,4,5,8-naphthalene-tetracarboxylic dianhydride (NTCDA) as acceptor layer, on substrate of glass covered by Al doped ZnO (AZO) layer. These heterostructures have been prepared using laser techniques: pulsed laser deposition (PLD) in an atmosphere of oxygen for AZO films deposition and matrix assisted pulsed laser evaporation (MAPLE) for organic films deposition. The influence of the deposition conditions on the transmission of the organic films has been analysed. The effect of the oxygen plasma treatment, with duration of 5 min and 10 min, on the surface topography, structural and optical properties of AZO layers deposited by PLD and, as consequence, on the optical and electrical properties of the single layer (ZnPc) and bi-layer (ZnPc/NTCDA) organic heterostructure, deposited by MAPLE, was investigated. (C) 2014 Elsevier B.V. All rights reserved.

503. Topological properties of the mesoscopic graphene plaquette: Quantum spin Hall effect due to spin imbalance

Authors: Ostahie, B; Nita, M; Aldea, A

Published: APR 15 2014, PHYSICAL REVIEW B, 89, DOI: 10.1103/PhysRevB.89.165412

We study the electronic properties of the confined honeycomb lattice in the presence of the intrinsic spin-orbit (ISO) interaction and perpendicular magnetic field, and report on uncommon aspects of the quantum spin Hall conductance corroborated by peculiar properties of the edge states. The ISO interaction induces two specific gaps in the Hofstadter spectrum, namely the "weak" topological gap defined by Beugeling et al. [Phys. Rev. B 86, 075118 (2012)], and spin-imbalanced gaps in the relativistic range of the energy spectrum. We analyze the evolution of the helical states with the magnetic field and with increasing Anderson disorder. The "edge" localization of the spin-dependent states and its dependence on the disorder strength is shown. The quantum transport, treated in the Landauer-Buttiker formalism, reveals interesting new plateaus of the quantum spin Hall effect (QSHE), and also of the integer quantum Hall effect (IQHE), in the energy ranges corresponding to the spin-imbalanced gaps. The properties of the spin-dependent transmittance matrix that determine the symmetries with respect to the spin, energy, and magnetic field of the longitudinal and transverse resistance are shown.

504. Covalent Functionalization of Graphene Oxide with Cisplatin

Authors: Ciobotaru, CC; Damian, CM; Matei, E; Iovu, H

Published: MAR 2014, MATERIALE PLASTICE, 51, 80, DOI:

The objective of this study was to obtain graphene oxide starting from graphite and to covalently functionalize this nanomaterial with Cisplatin. The presence of the drug was pointed out using different methods like FTIR Spectroscopy, X-Ray Photoelectron Spectroscopy (XPS), Thermogravimetric analysis (TGA), RAMAN Spectroscopy, X-Ray Diffraction and Scanning electron microscopy (SEM).

505. Cell Adhesion Response on Femtosecond Laser Initiated Liquid Assisted Silicon Surface

Authors: Ulmeanu, M; Sima, LE; Ursescu, D; Enculescu, M; Bazan, X; Quintana, I

Published: MAR 2014, CURRENT TOPICS IN MEDICINAL CHEMISTRY, 14, 629, DOI: 10.2174/1568026614666140118204946

Silicon substrates were irradiated at normal incidence with a femtosecond Ti:sapphire laser (Quatronix, 90 fs pulse duration, 1 kHz repetition rate, M-2 similar to 1.2, maximum energy peak 350 mJ) operating at a wavelength of 400 nm and focused via a microscope objective (Newport; UV Objective Model, 37x 0.11 N.A.). The laser scanning was assisted by liquids precursors media such as methanol and 1,1,2-trichlorotrifluoroethane. By altering the processing parameters, such as incident laser energy, scanning speed, and different irradiation media, various surface structures were produced on areas with 1 mm 2 dimensions. We analyzed the dependence of the surface morphology on laser pulse energy, scanning speed and irradiation media. Well ordered areas are developed without imposing any boundary conditions for the capillary waves that coarsens the ripple pattern. To assess biomaterial-driven cell adhesion response we investigated actin filaments organization and cell morphological changes following growth onto processed silicon substrates. Our study of bone cell progenitor interaction with laser nanoprocessed silicon lines has shown that cells anchor mainly to contact points along the nanostructured surface. Consequently, actin filaments are stretched towards the 15 mu m wide parallel lines increasing lateral cell spreading and changing the bipolar shape of mesenchymal stem cells.

506. Indium-tin nanoscaled oxides synthesized under hydrothermal supercritical and postannealing pathway: Phase dynamics and characterization

Authors: Diamandescu, L; Tarabasanu-Mihaila, D; Feder, M; Enculescu, M; Teodorescu, VS; Constantinescu, S; Popescu, T; Bartha, C; Pap, Z

Published: FEB 14 2014, MATERIALS CHEMISTRY AND PHYSICS, 143, 1549, DOI: 10.1016/j.matchemphys.2013.11.064

With the aim of synthesizing the mixed nanoparticle system xIn(2)O(3)-(1-x)SnO2 over all molar concentration range 0 <= x <= 1, Delta x = 0.1, we performed hydrothermal supercritical experiments on indium-tin hydrogel resulted from InCl3-SnCl4 water solution. Nanophases isostructural with InOOH and SnO2 were obtained by hydrothermal reaction at 400 degrees C, in the molar concentration range of 0.1 <= x <= 0.7; at x = 0.8 and x = 0.9 only one phase, isostructural with InOOH, was observed. Samples calcined at 500 degrees C with x in the range of 0.2 <= x <= 0.7 contain a nanoscaled phase isostructural with rhombohedral In2O3 and a second one isostructural with tetrahedral SnO2. At x = 0.8 and x = 0.9 only one phase isostructural with rhombohedral In2O3 appears: rhombohedral ITO phase. The determined band gap energies could recommend the rhombohedral ITO structure for visible light photocatalytic applications. The phase dynamics together with the concentration range for existence of the solid solutions in the InOOH-SnO2 and In2O3-SnO2 composite semiconducting nanoparticle systems have been evidenced and discussed. (C) 2013 Elsevier B.V. All rights reserved.

507. Thermally activated conversion of a silicate gel to an oxyfluoride glass ceramic: Optical study using Eu3+ probe ion

Authors: Secu, CE; Bartha, C; Polosan, S; Secu, M

Published: FEB 2014, JOURNAL OF LUMINESCENCE, 146, 543, DOI: 10.1016/j.jlumin.2013.10.013

Sol-gel route using metal alkoxides precursor and trifluoroacetic acid as in situ fluorination reagent has been used to prepare Eu3+ -doped silicate xerogel, followed by thermal annealing to obtain oxyfluoride glass ceramic containing Eu3+ -doped BaF2 nanocrystals. We have used Eu3+ as probe ion and we analyzed its characteristic features (photoluminescence, optical absorption and magnetic circular dichroism) to get information about the local environment around the ion during thermally activated evolution of the sol to xerogel and then glass ceramic. As the drying and annealing proceeds silica network is formed accompanied by precipitation of the nanofluoride crystalline phase; Eu3+ coordination changes gradually from a random and assymetric CF3COO- one (in the sol) to a symmetric one (in the BaF2 nanocrystals) given by the fluorine ions. Glass ceramization is based on a homogenous crystallization mechanism with BaF2 nucleation centres resulted from thermal decomposition of Ba-trifluoacetate at around 300 degrees C followed by subsequent growth into BaF2 nanocrystals above 600 degrees C; Eu3+-ions are incorporated during the nanocrystals growth. (C) 2013 Elsevier B.V. All rights reserved.

508. Polysaccharide-assisted crystallization of ZnO micro/nanostructures

Authors: Preda, N; Enculescu, M; Enculescu, I

Published: JAN 15 2014, MATERIALS LETTERS, 115, 260, DOI: 10.1016/j.matlet.2013.10.081

ZnO micro/nanostructures with complex morphology were synthesized by a simple chemical reaction between zinc nitrate and hexamethylenetetramine in the presence of polysaccharides. X-ray diffraction analysis showed that all obtained samples are of wurtzite structure. The reflectance and room temperature photoluminescence spectra have been used to investigate the optical properties of the ZnO structures. The scanning electron microscopy images reveal that the ZnO morphology (star, double-jellyfish, double-raspberry and edelweiss-flower) can be easily changed by varying the polysaccharides: sodium alginate, gum arabic and chitosan. The polysaccharide-assisted crystallization method could provide a facile approach to synthesize other desired compounds with controllable morphology. (C) 2013 Elsevier B.V. All rights reserved.

509. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

510. Dual emitter IrQ(ppy)(2) for OLED applications: Synthesis and spectroscopic analysis

Authors: Ciobotaru, IC; Polosan, S; Ciobotaru, CC

Published: JAN 2014, JOURNAL OF LUMINESCENCE, 145, 262, DOI: 10.1016/j.jlumin.2013.07.067

The synthesis of organometallic compound with iridium and two types of ligands, quinoline and phenylpyridine, was done successfully. The absorption spectra of this compound have shown broad peaks in a visible region assigned to metal-to-ligands charge transfer and in UV region assigned to intraligand absorptions. The photoluminescence spectra exhibit dual character in which the red emission is more intense than the green one. In cathodoluminescence measurements, under electron beam, the powder obtained after recrystallization from dichloromethane, shows similar behaviors with photoluminescence spectra. The cathodoluminescence images have shown a luminescent crystalline powder with triclinic structure. This compound exhibits combined vibrational modes, which proves the presence in the same molecule of both ligands. Density Functional Theory calculation was involved in order to identify the main vibrations of this compound. (C) 2013 Elsevier B.V. All rights reserved.