National Institute Of Materials Physics - Romania

Publications

839 articles found

411. Influence of 2,2 '-bipyridine on oxidative dissolution of iron monosulfide

Authors: Chirita, P; Badica, CE; Constantin, CA; Birsa, LM; Matei, E; Baibarac, M

Published: OCT-NOV 2014, SURFACE AND INTERFACE ANALYSIS, 46, 846, DOI: 10.1002/sia.5459

The 2,2'-bipyridine effects on iron monosulfide (FeS) oxidative dissolution rates have been examined by potentiodynamic polarization and electrochemical impedance spectroscopy. The adsorption of 2,2'-bipyridine to synthetic FeS was investigated by batch adsorption experiments, SEM, energy-dispersive X-ray analysis and Raman spectroscopy. The experiments were performed in air-saturated solutions at pH 5, 25 degrees C and an ionic strength of I = 0.004 M NaCl. Correlation between oxidative dissolution rates and 2,2'-bipyridine adsorption suggests that FeS oxidative dissolution is the result of two antagonistic processes: (i) the inhibiting adsorption of 2,2'-bipyridine on mineral surface and (ii) the promoting effect of 2,2'-bipyridine on the iron dissolution from FeS surface. Copyright (C) 2014 John Wiley & Sons, Ltd.

412. Ultraviolet and visible up-conversion luminescence of Er3+/Yb3+ co-doped CaF2 nanocrystals in sol-gel derived glass-ceramics

Authors: Georgescu, S; Voiculescu, AM; Matei, C; Secu, CE; Negrea, RF; Secu, M

Published: NOV 2013, JOURNAL OF LUMINESCENCE, 143, 156, DOI: 10.1016/j.jlumin.2013.04.002

Glass-ceramics containing Er3+/Yb3+ codoped CaF2 nanocrystals have been prepared by using the controlled crystallization above 650 degrees C of the (Yb3+/Er3+) codoped CaF2-SiO2 xerogels. X-ray diffraction and scanning electron microscopy data have revealed the formation of CaF2 nanoctystals of about 16 nm size. For pumping at 973 nm, this glass-ceramics shows, besides green and red up-conversion luminescence, violet (at similar to 408 nm) and near-ultraviolet emission (at similar to 380 nm). The mechanisms responsible for the upconversion luminescence are presented and discussed. The fluorescence lifetimes of the metastable levels responsible for violet, green and red luminescence are measured and their quantum efficiencies are estimated. (C) 2013 Elsevier B.V. All rights reserved.

413. EFFECT OF THERMAL ANNEALING ON THE STRUCTURAL AND OPTICAL PROPERTIES OF Ag/As2S3 MULTILAYERS

Authors: Sava, F; Lorinczi, A; Velea, A; Simandan, ID; Preda, N; Socol, G; Mihailescu, IN; Zamfira, CS; Cretu, NC; Popescu, M

Published: NOV 2013, CHALCOGENIDE LETTERS, 10, 471, DOI:

A complex structure of four double layers of Ag / As2S3 has been deposited by Pulsed Laser Deposition method on a glass substrate. The effects of thermal annealing on the structural and optical properties were investigated. An effect of layer mixing has been evidenced.

414. COMPLEX LANGMUIR-BLODGETT FILMS BASED ON BARIUM STEARATE MULTILAYERS WITH CARBON NANOTUBES AND As2S3 NANOPARTICLES

Authors: Simandan, ID; Sava, F; Popescu, M; Lorinczi, A

Published: NOV 2013, CHALCOGENIDE LETTERS, 10, 484, DOI:

We have prepared complex multilayer films based on Barium stearate. The multilayer samples have been deposited by the Langmuir-Blodgett technique. The complex multilayers were also deposited on body sensor. The sample was then subjected to the illumination with UV light. We observed changes in the resistivity of the multilayer during the illumination

415. Luminescent Eosin Y-SiO2 hybrid nano and microrods prepared by sol-gel template method

Authors: Secu, M; Secu, CE; Sima, M; Negrea, RF; Bartha, C; Dinescu, M; Damian, V

Published: NOV 2013, JOURNAL OF LUMINESCENCE, 143, 92, DOI: 10.1016/j.jlumin.2013.04.043

Sol-gel chemistry within the pores of a polycarbonate template membrane was used for the preparation of Eosin Y-SiO2 hybrid nano- and microrods, using tetraethylorthosilicate [TEOS, Si(OC2H5)(4)] as the precursor in the presence of trifluoroacetic acid (TFA) catalyst. The ethanolic solution of Eosin-Y was added to the silica sal to trap dye molecules inside the SiO2 gel network during the gelation. Structural and morphological characterization using scanning electron microscopy (SEM) and luminescence microscopy have shown the formation of rods with 200 nm and 1.2 mu m diameter and about 30 mu m length, exhibiting luminescence properties. Spectroscopic characterization has shown that the luminescence is due to Eosin-Y molecule in the xerogel porous network, surrounded by a solvation shell given mainly by the water. (C) 2013 Elsevier B.V. All rights reserved.

416. Synthetic fabrics coated with zinc oxide nanoparticles by electroless deposition: Structural characterization and wetting properties

Authors: Frunza, L; Preda, N; Matei, E; Frunza, S; Ganea, CP; Vlaicu, AM; Diamandescu, L; Dorogan, A

Published: OCT 1 2013, JOURNAL OF POLYMER SCIENCE PART B-POLYMER PHYSICS, 51, +, DOI: 10.1002/polb.23346

Electroless deposition was successfully applied in developing crystalline particles of zinc oxide onto polyester textile materials; this deposition is here presented in comparison with other materials made from poly(lactic acid), polyamide or hemp. Structural and spectroscopic characterization of the raw and deposited samples has been performed. The structure of zinc oxide particles was that of wurtzite type as indicated by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Crystallites were 20-500 nm in diameter and up to 1 mu m in length. The grown particles cover the fibers not only on the fabric surface but in the textile depth. Contact angle measurement by the sessile drop method was used to study the wettability behavior of the investigated composite systems. The hierarchical roughness structure generates superhydrophobic properties onto polyester fabrics, for which water contact angles exceed 150 degrees. The other functionalized samples also become more hydrophobic after deposition. Cassie-Baxter model was found suitable to describe the behavior, though the fraction of surface occupied by the water-solid interface is high enough. The electroless deposition technique applied previously for cotton fabrics was once more proven to be highly reproducible, easy scalable, and cheap, allowing a wide range of applications. (c) 2013 Wiley Periodicals, Inc.

417. Effect of broadband light on Ag/As2S3 multilayers

Authors: Sava, F; Velea, A; Popescu, M; Lorinczi, A; Simandan, ID; Vlaicu, AM; Socol, G; Mihailescu, IN; Stefan, N

Published: OCT 1 2013, JOURNAL OF NON-CRYSTALLINE SOLIDS, 377, 161, DOI: 10.1016/j.jnoncrysol.2013.02.023

A sandwich structure of four double layers of Ag (5 nm)/As2S3 (82.7 nm) has been prepared by Pulsed Laser Deposition (PLD) method. The effect of broadband light on the multilayer structure has been investigated. The X-ray reflectivity (XRR) patterns after different irradiation times have been measured. Although the fully intermixing of Ag and As2S3 layers should be expected during irradiation with visible light, however even after 5 h of irradiation the intermixing is not completed. The characteristic features of XRR diagrams for long irradiation times have been interpreted by scattering of X-ray radiation on clusters of Ag or Ag-As2S3. (c) 2013 Elsevier B.V. All rights reserved.

418. Eu3+ probe ion for rare-earth dopant site structure in sol-gel derived LiYF4 oxyfluoride glass-ceramic

Authors: Secu, CE; Negrea, RF; Secu, M

Published: OCT 2013, OPTICAL MATERIALS, 35, 2460, DOI: 10.1016/j.optmat.2013.06.053

Sol-gel route using metal alkoxides and trifluoroacetic acid as precursors has been used to prepare oxyfluoride glass-ceramic containing Eu3+-doped LiYF4 nanocrystals of about tens of nm size embedded in a silica matrix through controlled crystallization at higher temperatures of the xerogel. Photoluminescence spectra and decay curves recorded in the Eu3+-doped LiYF4 polycrystalline pellet and glass ceramic have been discussed using group-theoretical arguments. In the glass-ceramic Eu3+ ions are embedded dominantly inside the LiYF4 nanocrystals most probably as Eu-O center and/or dimer centers in low symmetry (C-2v) sites; oxygen ions were incorporated in their neighborhood during the glass ceramization. (C) 2013 Elsevier B.V. All rights reserved.

419. Morphological and structural characterization of SiC based composite nanostructures

Authors: Filipescu, M; Stokker-Cheregi, F; Colceag, D; Nedelcea, A; Birjega, R; Nistor, LC; Dinescu, M

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 100, DOI: 10.1016/j.apsusc.2013.03.166

This paper reports on producing SiC based nanostructures (SiC, W-SiC, CNS-SiC) by pulsed laser deposition (PLD) and radio-frequency plasma assisted PLD. Simple and composite targets (SiC, 3/4 SiC + 1/4 tungsten and 3/4 SiC + 1/4 graphite) were irradiated by a 266 nm pulsed laser beam having a pulse duration of 7 ns. The silicon substrates were kept either at room temperature or heated up to 600 degrees C. The depositions were performed in argon at various pressures, ranging from 0.05 mbar up to 2 mbar. The influence of deposition parameters on the structure, surface morphology and composition of different SiC based structures was studied by atomic force microscopy, scanning electron microscopy, secondary ion mass spectrometry, transmission electron microscopy and selected area electron diffraction. Fibers, tubes, nanoparticles and rolled sheets structures were obtained by varying laser fluence, substrate temperature, gas pressure and radio-frequency power. (C) 2013 Elsevier B. V. All rights reserved.

420. Growth and structural characterization of orthorhombic and tetragonal SrCuO2 thin films

Authors: Mihailescu, CN; Pasuk, I; Athanasopoulos, GI; Luculescu, C; Socol, M; Saint-Martin, R; Revcolevschi, A; Giapintzakis, J

Published: AUG 1 2013, APPLIED SURFACE SCIENCE, 278, 135, DOI: 10.1016/j.apsusc.2012.12.029

Epitaxial SrCuO2 thin films were grown on (0 0 1) SrTiO3 substrates by pulsed laser deposition using a stoichiometric target. X-ray diffraction indicated that the SrCuO2 films undergo a structural phase transition as a function of the substrate temperature. Films deposited at temperatures below 600 degrees C exhibit a tetragonal phase with the c-axis oriented along the growth direction while films deposited at temperatures above 700 degrees C exhibit an orthorhombic phase with the b-axis oriented along the growth direction. Atomic force microscopy indicated that the as-grown film surfaces are rather smooth and the roughness increases with increasing substrate temperature. Energy dispersive X-ray spectroscopy in agreement with X-ray diffraction intensity ratio data revealed that all films are non-stoichiometric and contain Sr vacancies (Sr/Cu similar to 0.8). The influence of film-substrate lattice matching and substrate temperature on the structural phase transition is discussed. (C) 2012 Elsevier B.V. All rights reserved.