National Institute Of Materials Physics - Romania

Publications

860 articles found

481. Characterization of hydrogenated and deuterated thin carbon films deposited by magnetron sputtering

Authors: Pantelica, D; Ionescu, P; Petrascu, H; Nita, CR; Matei, E; Rasoga, O; Acsente, T; Dinescu, G

Published: JUL 15 2014, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 331, 124, DOI: 10.1016/j.nimb.2014.01.029

Thin films of C layers were deposited by radiofrequency magnetron sputtering on silicon substrates using three gaseous atmospheres: pure Ar, Ar + H-2 and Ar + D-2 mixtures. Scanning Electron Microscopy investigations showed that addition of D-2 or H-2 to main sputtering gas (Ar) leads to the enhancement of the deposition rate while the layer morphology remained columnar. Fourier Transform Infrared Spectroscopy measurements revealed the presence of D-C or H-C chemical bonds in the samples. Ion beam analysis measurements performed by simultaneous recording of the recoiled H and D ions, and of backscattered He-4 confirmed the incorporation of hydrogen and deuterium in the deposited carbon thin films. (C) 2014 Elsevier B.V. All rights reserved.

482. High magnetic field enhancement of the critical current density by Ge, GeO2 and Ge2C6H10O7 additions to MgB2

Authors: Batalu, D; Aldica, G; Popa, S; Miu, L; Enculescu, M; Negrea, RF; Pasuk, I; Badica, P

Published: JUL 1 2014, SCRIPTA MATERIALIA, 82, 64, DOI: 10.1016/j.scriptamat.2014.03.024

Ge, GeO2 and Ge2C6H10O7 additions to MgB2 obtained by ex situ spark plasma sintering significantly enhance the critical current density J(c) in high magnetic fields. A J(c)(T = 20 K) of 102 A cm(-2) is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB2(Ge2C6H10O7)(0.0014) sample. The decrease in the critical temperature for added samples is less than 1 K and T-c(20 K, H = 0) shows a small decrease from 5.5 x 10(5) A cm(-2) in the pristine sample to 3.9 x 10(5) A cm(-2) in MgB2(Ge2C6H10O7)(0.0014) sample. Ge does not substitute into the MgB2 lattice. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

483. Micropatterned ZnO rod arrays prepared by Au-catalyzed electroless deposition

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

Published: JUL 2014, PHYSICA STATUS SOLIDI-RAPID RESEARCH LETTERS, 8, 652, DOI: 10.1002/pssr.201409089

Micropatterned ZnO was synthesized by an electroless deposition process using Au stripes as catalytic surfaces. The Au-patterned electrodes were prepared on SiO2/Si wafers using photolithography. The site-selective deposition of patterned ZnO hexagonal rod arrays is confirmed by scanning electron microscopy. The ZnO micropatterned surface revealed a conversion of wettability from hydrophilic to super-hydrophobic depending on the deposition reaction parameters. The electrical measurements carried out at room temperature before and after exposure to ammonia vapors of the patterned ZnO arrays show a resistance variation with exposure time. Highly reproducible, easy scalable and low-cost, photolithography and electroless deposition techniques could provide a facile approach to fabricate functionalized micropatterns, for a wide range of applications. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

484. 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.

485. 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.

486. 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.

487. 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).

488. 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.

489. 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.

490. 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.