National Institute Of Materials Physics - Romania

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860 articles found

521. 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.

522. Structural, electric and magnetic properties of Pb(Zr0.2Ti0.8)O-3-CoFe2O4 heterostructures

Authors: Chirila, C; Ibanescu, G; Hrib, L; Negrea, R; Pasuk, I; Kuncser, V; Pintilie, I; Pintilie, L

Published: OCT 31 2013, THIN SOLID FILMS, 545, 7, DOI: 10.1016/j.tsf.2013.06.033

Electric and magnetic properties of symmetric and asymmetric Pb(Zr-0.2 Ti-0.8)O-3-CoFe2O4 (PZT/CFO) heterostructures, grown by pulsed laser deposition on SrTiO3 (100) substrates with a 25 nm SrRuO3 (SRO) buffer layer as bottom electrode, were investigated by using hysteresis and capacitance measurements. X-ray diffraction, and transmission electron microscopy investigations reveal the high quality crystalline structure and the epitaxial relationship between SRO, PZT and CFO. The electric polarization-voltage hysteresis reveals that the remnant polarization and the coercive field are significantly affected by the CFO layer. The frequency dependence of capacitance suggests a Maxwell-Wagner type relaxation at low frequencies and is also affected by the presence of the PZT/CFO interface(s). The magnetic hysteresis measurements infer the possible presence of another spinel phase (Co3O4) in the CFO film, due to the lattice mismatch at the PZT/CFO interfaces, and with direct influence on the magnetic response of the structure. According to the electric and magnetic characterization, better room temperature multiferroic properties would be expected for the symmetric heterostructure. (C) 2013 Published by Elsevier B. V.

523. Sequential Thermal Decomposition of the Shell of Cubic ZnS/Zn(OH)(2) Core-Shell Quantum Dots Observed With Mn2+ Probing Ions

Authors: Nistor, SV; Ghica, D; Stefan, M; Nistor, LC

Published: OCT 24 2013, JOURNAL OF PHYSICAL CHEMISTRY C, 117, 22028, DOI: 10.1021/jp4063093

Thermally induced changes in the structure and composition of the shell of tightly aggregated cubic ZnS/Zn(OH)(2) core shell quantum dots of 1.9 nm average core size were investigated by multifrequency electron paramagnetic resonance of Mn2+ probing ions. The observed three-steps temperature induced transformation of the Mn2+ surface centers in the 80-450 degrees C temperature range Zn(OH)(2) shell into ZnO, with the formation of the Zn2O(OH)(2) and Zn4O3(OH)(2) intermediate nanocompounds. The presence of a 0.3 to 1.9 nm thick surface layer of disordered nanomaterial separating the cubic ZnS cores and its shrinking to a few atomic layers by mass loss after annealing up to 350 degrees C was observed by high resolution transmission electron microscopy. Unlike the single step dehydration around 120 degrees C of the bulk epsilon-Zn(OH)(2), the complex decomposition of the epsilon-Zn(OH)(2) shell is attributed to its nanosized, disordered structure.

524. 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.

525. 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.

526. 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.

527. Dense Ge nanocrystal layers embedded in oxide obtained by controlling the diffusion-crystallization process

Authors: Lepadatu, AM; Stoica, T; Stavarache, I; Teodorescu, VS; Buca, D; Ciurea, ML

Published: SEP 15 2013, JOURNAL OF NANOPARTICLE RESEARCH, 15, DOI: 10.1007/s11051-013-1981-y

Amorphous Ge/SiO2 multilayer structures deposited by magnetron sputtering have been annealed at different temperatures between 650 and 800 degrees C for obtaining Ge nanocrystals in oxide matrix. The properties of the annealed structures were investigated by transmission electron microscopy, Raman spectroscopy, and low temperature photoluminescence. The Ge crystallization is partially achieved at 650 degrees C and increases with annealing temperature. Insight of the Ge nanocrystal formation was acquired by comparing two annealing procedures, i.e., in a conventional tube furnace and by a rapid thermal annealing. By rapid thermal annealing in comparison to conventional furnace one, the Ge crystallization process is faster than Ge diffusion, resulting in the formation of more compact layers of Ge nanocrystals with 8-9.5-nm size as Raman spectroscopy reveals. These findings are important to improve the annealing efficiency in the nanocrystals formation for a precise control of their sizes and location in oxide matrix and for the possibility to create systems with interacting nanoparticles for charge or excitonic transfer. The infrared photoluminescence of Ge nanocrystals at low temperatures shows strong emission with two sharp peaks at about 1,000 meV.

528. NO2 sensing mechanism of ZnO-Eu2O3 binary oxide under humid air conditions

Authors: Stanoiu, A; Simion, CE; Somacescu, S

Published: SEP 2013, SENSORS AND ACTUATORS B-CHEMICAL, 186, 694, DOI: 10.1016/j.snb.2013.06.083

In order to understand the role of ambient humidity on NO2 detection, electrical resistance and work function changes were recorded simultaneously on ZnO-Eu2O3 material. Thus, surface band bending and electron affinity could be evaluated, according to the Schottky model. The lack of electron affinity changes during NO2 exposure in dry air conditions, reveals that only the free charge concentration is affected. Exposure to NO2 in humid background leads to an increase in sensor signals and a significant change in the electron affinity as well. This effect suggests an interaction between NO2 and surface hydroxyl species; thereby additional charge carriers are involved in the overall sensing process. High resolution XPS analysis proves the presence of Eu solely in the 3(+) oxidation state before and after NO2 exposure. A gas-sensing interaction mechanism has been proposed. (C) 2013 Elsevier B.V. All rights reserved.

529. Nanosize induced effects in luminescent ZnS:Mn2+ quantum dots

Authors: Nistor, SV; Stefan, M; Ghica, D; Nistor, LC

Published: SEP 2013, RADIATION MEASUREMENTS, 56, 43, DOI: 10.1016/j.radmeas.2013.01.046

Nanocrystals (NCs) of II-VI semiconductors of few nanometers average size, called quantum dots (QDs), are now intensely investigated as radiation detectors. Besides the expected quantum confinement and influence of surface states, our electron paramagnetic resonance investigations of cZnS QDs doped with Mn2+ ions, correlated with structural data, underline that other properties should be also taken into consideration in developing the II VI semiconductor QDs as radiation detectors. Thus, the preferential localization of Mn2+ in the core of the cubic ZnS QDs at substitutional Zn2+ cation sites next to a stacking lattice defect is expected to lead, besides changes in the impurity energy levels, to specific aggregation properties. An outer shell of different composition can also influence the structural properties of the QDs core with effects on the optical properties as well. (C) 2013 Elsevier Ltd. All rights reserved.

530. Weighting the influence of TiO2 anatase/brookite ratio in TiO2-Ag porous nanocomposites on visible photocatalytic performances

Authors: Iancu, V; Baia, M; Diamandescu, L; Pap, Z; Vlaicu, AM; Danciu, V; Baia, L

Published: AUG 15 2013, MATERIALS CHEMISTRY AND PHYSICS, 141, 239, DOI: 10.1016/j.matchemphys.2013.05.005

Nanocomposites based on TiO2 aerogel and Ag nanoparticles have been successfully obtained through different synthesis methods and their specific surface areas have been determined by N-2 sorption (BET method). The photocatalytic potential for salicylic acid degradation has been evaluated. It was found that under visible light irradiation, all synthesized nanocomposites exhibit higher photocatalytic activity than the commercially available Aeroxide P25. By correlating the structural parameters with the photocatalytic performances, it has been found that the Ag nanoparticles and brookite phase presence alongside the anatase play important roles on the visible photocatalysts behavior. For the Ag containing samples with mixed anatase brookite phases, it has been observed that the visible photocatalytic performance decreases with the increase in brookite crystalline phase content. On the other hand, the addition of Ag nanoparticles results, as expected, in a clear enhancement of the visible photocatalytic activity. (C) 2013 Elsevier B.V. All rights reserved.