National Institute Of Materials Physics - Romania

Publications

5714 articles found

2541. Effect of maleic anhydride-aniline derivative buffer layer on the properties of flexible substrate heterostructures: Indium tin oxide/nucleic acid base/metal

Authors: Stanculescu, A; Socol, M; Socol, G; Mihailescu, IN; Girtan, M; Preda, N; Albu, AM; Stanculescu, F

Published: DEC 1 2011, THIN SOLID FILMS, 520, 1258, DOI: 10.1016/j.tsf.2011.04.204

This paper presents some investigations on the properties of guanine (G) and cytosine (C) based heterostructures deposited on flexible substrates. The effects of two types of maleic anhydride-aniline derivatives (maleic anhydride-cyano aniline or maleic anhydride-2,4 dinitroaniline) buffer layer, deposited between indium tin oxide and (G) or (C) layer, on the optical and electrical properties of the heterostructures have been identified. The heterostructures containing a film of maleic anhydride-2,4 dinitroaniline have shown a good transparency and low photoluminescence invisible range. This buffer layer has determined an increase in the conductance only in the heterostructures based on (G) and (C) deposited on biaxially-oriented polyethylene terephthalate substrate. (C) 2011 Elsevier B. V. All rights reserved.

2542. X-ray absorption fine structure investigations on heat-treated Cr-doped titania thin films

Authors: Mardare, D; Nica, V; Pohoata, V; Macovei, D; Gheorghe, N; Luca, D; Teodorescu, CM

Published: DEC 1 2011, THIN SOLID FILMS, 520, 1352, DOI: 10.1016/j.tsf.2011.04.124

Chromium-doped titanium oxide thin films were investigated in the as-deposited state and after thermal treatment (723 K for 3 h in air). X-ray diffraction data revealed an improvement in film crystallinity induced by the thermal treatment. Extended X-ray absorption fine structure data revealed similar atomic neighboring around Cr atoms in both as-deposited and annealed samples. A lattice contraction of similar to 2% is observed in the annealed samples. The 67% enhancement of the amplitude of the Cr 1 s X-ray absorption fine structure pre-edge peak after thermal treatment, which is a sign of "dipole-forbidden" 1 s -> 3 d transitions, suggests strong alteration in the number of Cr 3 d vacancies, in spite of similar Cr local environment in the two kinds of investigated samples. We discuss here the Cr+ -> Cr4+ and Cr2+ -> Cr6+ changes induced by thermal treatment, and/or the evolution in local structures without inversion center. Refractive index dispersion spectra in the visible wavelength domain allowed us to compute the values of the dispersion energy, the single-oscillator energy and the coordination number of Ti atoms in both as-deposited and annealed samples. (C) 2011 Elsevier B. V. All rights reserved.

2543. Eu3+ LUMINESCENCE IN As2S3 DOT NETWORK

Authors: Georgescu, S; Popescu, M; Sava, F; Velea, A; Pavelescu, G

Published: DEC 2011, CHALCOGENIDE LETTERS, 8, 738, DOI:

Thin films of As2S3 doped with Eu3+ were prepared by vacuum evaporation. It was measured the fluorescence spectra before and after a heat treatment at 180 degrees C for 45 minutes in inert atmosphere. After the heat treatment the transitions D-5(1) -> F-7(1), D-5(0) -> F-7(1) and D-5(0) -> F-7(2) were evidenced in the luminescence spectrum.

2544. Pure, smooth and dense W films obtained by an anodic arc plasma

Authors: Surdu-Bob, CC; Racolta, PM; Badulescu, M; Chiojdeanu, C; Arsene, N; Logofatu, C; Ionescu, C; Sporea, D; Gruia, I

Published: DEC 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 1340, DOI:

Tungsten films have a number of important applications. The techniques to produce quality films are very few and most of them use gases as precursors or as buffer. The Thermoionic Vacuum Arc (TVA) plasma is an original technique capable of producing pure, dense and very smooth Tungsten films of thicknesses from nanometers to tens of micrometers with no buffer gas or gas precursors. This paper presents characterisation of Tungsten films obtained by TVA in terms of composition and topography using XRF, XPS and AFM. The films studied are pure and contain a very thin surface oxide of WO(3). The influence of water vapors inherently present on the chamber walls to the film surface composition is also presented.

2545. In situ electrical conductivity and catalytic properties of copper ferrite synthesized by non-conventional methods

Authors: Munteanu, C; Caldararu, M; Gingasu, D; Feder, M; Diamandescu, L; Ionescu, NI

Published: DEC 2011, REACTION KINETICS MECHANISMS AND CATALYSIS, 104, 368, DOI: 10.1007/s11144-011-0357-5

The in situ electrical properties and the catalytic activity of copper ferrite obtained by co-precipitation and thermal decomposition of polynuclear coordination compounds were studied in the propane oxidation reaction. The sample prepared by complexation had a better catalytic activity. Based on the conductivity data and the relative phase distribution in fresh and used compounds, the results are discussed in terms of the redox-type mechanism.

2546. Improving TiO2 activity in photo-production of hydrogen from sugar industry wastewaters

Authors: M. Ilie, B. Cojocaru, B V.I. Parvulescu, H. Garcia

Published: DEC 2011, International Journal of Hydrogen Energy, 36, DOI: 10.1016/j.ijhydene.2011.09.029

A series of TiO2 photocatalysts dispersed on SiO2, modified with metals (Mn, Cr, V) or nonmetals (N or S) or covered with Au nanoparticles were prepared by incipient wetness impregnation, impregnation with urea or thiourea, and deposition-precipitation, respectively. The photocatalysts where characterized by chemical analysis, X-ray diffraction (XRD), diffuse reflectance UV-Vis spectroscopy (DR-UV-Vis) and Fourier transform infrared spectroscopy (FTIR). The photocatalytic activity was checked in the photo-generation of hydrogen from sugar solutions. The nature of the modifying species was found to influence the photoactivity and N and S led to more effective catalysts than metals. This behavior was attributed to the fact the N and S are less effective in forming recombination centers compared with the metals. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

2547. Spin dynamics in 57Fe-doped TiO2 anatase nanoparticles

Authors: Grecu, MN; Constantinescu, S; Tarabasanu-Mihaila, D; Ghica, D; Bibicu, I

Published: DEC 2011, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 248, 2931, DOI: 10.1002/pssb.201147124

In this paper we present electron paramagnetic resonance (EPR) and Mossbauer (transmission method, TMS and measurements in the scattering method, CEMS) experiments on Fe-57 (0.11at.%) doped nanocrystalline anatase-type TiO2, synthesized by a hydrothermal method. Different Fe3+ and Fe2+ ions positions, with various hyperfine interactions evidenced in Mossbauer spectra (MS), confirm a partial magnetic ordering at room temperature. The magnetic hyperfine fields in the TMS spectra, better resolved at lower temperatures, do not change essentially with temperature. The first CEMS measurements, carried out on iron-doped TiO2 nanoparticles, reveal a larger disorder in the surface particles layer. The temperature dependence of the double integral EPR spectral intensity, proportional with the sample susceptibility, shows an anomalous behaviour. It suggests the bound magnetic polaron (BMP) mechanism for the magnetic ordering.

2548. LUMINESCENCE OF ARSENIC SULPHIDE DOTS DOPED WITH EUROPIUM, PREPARED BY THERMAL EVAPORATION AND PULSED LASER DEPOSITION METHODS

Authors: Popescu, M; Velea, A; Simandan, ID; Sava, F; Lorinczi, A; Ghervase, L; Pavelescu, G; Mihailescu, IN; Socol, G; Georgescu, S

Published: DEC 2011, CHALCOGENIDE LETTERS, 8, 724, DOI:

Networks of dots made of As2S3 chalcogenide has been obtained by Vacuum Evaporation and Pulsed Laser Deposition from bulk glassy As2S3 by the adapted method of SCEV (screen evaporation method). A very thin layer of Eu2O3 was deposited from a different target in the final deposition process. After a heat treatment at 180 degrees C for 90 minutes in nitrogen atmosphere a structural transformation of the amorphous As2S3 to realgar (AsS) occurred in the PLD deposited dots and the network of dots develops a luminescence effect. (Received November 25, 2011; accepted December 2, 2011)

2549. Highly adherent bioactive glass thin films synthetized by magnetron sputtering at low temperature

Authors: Stan, GE; Pasuk, I; Husanu, MA; Enculescu, I; Pina, S; Lemos, AF; Tulyaganov, DU; El Mabrouk, K; Ferreira, JMF

Published: DEC 2011, JOURNAL OF MATERIALS SCIENCE-MATERIALS IN MEDICINE, 22, 2710, DOI: 10.1007/s10856-011-4441-1

Thin (380-510 nm) films of a low silica content bioglass with MgO, B2O3, and CaF2 as additives were deposited at low-temperature (150A degrees C) by radio-frequency magnetron sputtering onto titanium substrates. The influence of sputtering conditions on morphology, structure, composition, bonding strength and in vitro bioactivity of sputtered bioglass films was investigated. Excellent pull-out adherence (similar to 73 MPa) was obtained when using a 0.3 Pa argon sputtering pressure (BG-a). The adherence declined (similar to 46 MPa) upon increasing the working pressure to 0.4 Pa (BG-b) or when using a reactive gas mixture (similar to 50 MPa). The SBF tests clearly demonstrated strong biomineralization features for all bioglass sputtered films. The biomineralization rate increased from BG-a to BG-b, and yet more for BG-c. A well-crystallized calcium hydrogen phosphate-like phase was observed after 3 and 15 days of immersion in SBF in all bioglass layers, which transformed monotonously into hydroxyapatite under prolonged SBF immersion. Alkali and alkali-earth salts (NaCl, KCl and CaCO3) were also found at the surface of samples soaked in SBF for 30 days. The study indicated that features such as composition, structure, adherence and bioactivity of bioglass films can be tailored simply by altering the magnetron sputtering working conditions, proving that this less explored technique is a promising alternative for preparing implant-type coatings.

2550. Metallurgical phases and their magnetism at the interface of nanoscale MgB2/Fe layered structures

Authors: Sahoo, B; Keune, W; Kuncser, V; Becker, HW; Rohlsberger, R

Published: NOV 30 2011, JOURNAL OF PHYSICS-CONDENSED MATTER, 23, DOI: 10.1088/0953-8984/23/47/475702

We report on the characterization of metallurgical phases and their magnetism at the interfaces of nanoscale MgB2/Fe layered structures. MgB2/Fe-57 multilayers with varying layer thicknesses were prepared by vacuum deposition and investigated, before and after annealing by electrical resistance measurements, x-ray diffraction and Fe-57 conversion-electron Mossbauer spectroscopy (CEMS) down to 5 K. Interfacial Fe-B phases, such as Fe2B, were identified by CEMS. A superparamagnetic-to-ferromagnetic transition is observed with increasing Fe-57 film thickness. Ultrahigh vacuum annealing at 500 degrees C of the multilayers leads to strong diffusion of Fe atoms into the boundary regions of the MgB2 layers. MgB2 in the as-grown multilayers is non-superconducting. Structural disorder and the effect of Fe interdiffusion contribute to the suppression of superconductivity in the MgB2 films of all the as-grown multilayers and the thinner annealed multilayers. However, an annealed MgB2/Fe-57/MgB2 trilayer with thicker (500 angstrom) MgB2 layers is observed to be superconducting with an onset temperature of 25 K. At 5 K, the annealed trilayer can be conceived as being strongly chemically modulated, consisting of two partially Fe-doped superconducting MgB2 layers separated by an interdiffused weakly magnetic Fe-B interlayer, which is characterized by a low hyperfine magnetic field B-hf of similar to 11 T. This chemically modulated layer structure of the trilayer after annealing was verified by Rutherford backscattering.