National Institute Of Materials Physics - Romania

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839 articles found

681. Photosensitization of ZnO nanostructured thin films with organic dyes

Authors: Tazlaoanu, C; Ion, L; Socol, G; Socol, M; Mihailescu, IN; Stanculescu, F; Enculescu, I; Ionescu, F; Magherusan, L; Antohe, S

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1346, DOI:

We report in this contribution on the photosensitization effect of ZnO nanostructured thin films with copper-phthalocyanine (CuPc). ZnO films were prepared by pulsed laser deposition (PLD), on optical glass substrates, covered with 300 nm thick ITO films. The structure and morphology of ZnO films were optimized for photovoltaic-cell applications by controlling the growing conditions. ZnO films (wurtzite type) were (001) preferentially oriented in the growth direction. Organic dyes were vacuum sublimated on ZnO films, and subsequently a 300 nm thick copper film was vacuum sublimated on top of the structure, acting as an ohmic contact. Action spectra of ITO/ZnO/CuPc/Cu photovoltaic structures were recorded and a well defined response was observed in the range of absorption bands of organic dyes. The dark IN characteristics were also recorded, and electrical characterizations of the photovoltaic structures are given. The measured fourth quadrant IN characteristics under integral illumination (photoelement regime), allowed us to extract the typical photovoltaic cells parameters.

682. Raman and photoluminescence studies on low-dimensional PbI2 particles embedded in polymer matrix

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1361, DOI:

Pbl(2) crystallite incorporated in optically transparent polyacrylamide and poly (vinyl alcohol) matrix have been studied by Raman scattering, photoluminescence (PL) at low temperature and Scanning Electron Microscopy (SEM). The small particles of Pbl(2) embedded in different host matrix were prepared by: i) cooling to the room temperature a boiling saturated aqueous Pbl(2) solution containing polyacrylamide or poly (vinyl alcohol) and ii) by chemical reaction of KI and Pb(NO3)2 in aqueous polyacrylamide solution. In all cases, were identified hexagonal platelets of Pbl(2) and rods like particles. The rods are featured by a similar Raman spectrum and a specific green emission (cca 550 nm). Modification of the Raman and PL spectra results from a compressing effect produced by the penetration between the Pbl(2) layers of different molecular species. By compression the hybridized electronic level situated at the top of valence band, formed by the contribution.of the 6s and 5p states of Pb2+ and l ions, undergo a deformation that induces a weakness of the interaction between the lead ion and iodine electron within a layer so that the photoluminescence of intercalated Pbl(2) acquires the characteristics of Pb2+ emission when it is dissolved in an alkali halide crystal.

683. Semiconductor nanowires obtained by template method

Authors: Sima, M; Enculescu, I; Sima, M; Vasile, E

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1554, DOI:

One-dimensional structures having uniform diameters were prepared by electrochemical deposition using polycarbonate membranes as templates. Lead chalcogenides and ZnO tubes and rods growth processes were presented comparatively. The tendency of PbTe and PbSe semiconductors to grow as tubes both in membrane micro and nanopores was explained based on the absorption of lead ions on the pore wall.

684. The ferroectric-electric characterization of PZT-PbS composites

Authors: Stancu, V; Buda, M; Pintilie, L; Popescu, M; Sava, F

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1520, DOI:

A new method for the preparation of PbS/PZT composite materials is proposed. The PZT matrix has been obtained using the sol-gel method on Pt-coated Si substrates. The PbS (nano) crystals were subsequently obtained by dipping the porous PZT matrix in Pb(NO3)(2) and Na2S solutions at room temperature. The XRD spectra show the presence of the tetragonal phase of PZT. The microstructure of the film was analyzed using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The size of the PbS (nano)-particles at the sample's surface is about 25 nm, estimated from the AFM analysis. The roughness of the sample's surface is about 5 nm. The porosity of the composite, estimated from the SEM analysis in cross-section is smaller than for the reference PZT porous matrix. The equivalent dielectric constant of the composite increases by a factor of 4-5 in comparison with the porous PZT reference and does not depend on the thickness of the surface PbS (nano)-crystalline layer. The saturated polarization (Ps) value for the PZT-PbS composite is smaller than that corresponding to the bulk PZT but higher than for the reference porous PZT. We attribute these effects to the partial filling of the pores in the PZT matrix with PbS.

685. Light absorption process in CdSxSe1-x doped alumino-phosphate glass

Authors: Stanculescu, A; Stanculescu, F; Elisa, M

Published: APR 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 835, DOI:

We present a study of the effect of the crystallites composition and size on the optical properties of vitreous aluminophosphate matrix doped with CdSxSe1-x crystallites. The influences of the glass matrix composition and, heat treatment temperature and duration on the stoichiometry of the crystalline phase have been investigated by optical methods. We have studied the effect of the sodium oxide contained in the matrix, annealing temperature variation from 425 degrees C to 475 degrees C and duration variation from 2 h to 6 h on the light absorption process, evaluating an optical band gap energy between E-g=1.74 eV and E-g=2.29 eV associated with changes in the composition of the crystallites. The blue shift of the absorption edge observed in samples containing Na2O annealed at 425 degrees C for 4 h or at 450 degrees C for 2 h was attributed to a variation in the crystallites' composition because their size is not favourable to the quantum confinement. We have also investigated the effect of individual CdS and CdSe clusters on the absorption properties of the aluminophosphate glass and on the process of zinc incorporation in the crystalline phase. We have made some assumptions concerning the effect of the aluminophosphate glass matrix on the direct band to band light absorption mechanism characterising the II-IV bulk semiconductor.

686. Study of non catalytic oxidehydrogenation of isobutane in an integral reactor

Authors: Grecu, MN; Burducea, G; Grecu, V; Moldovan, R; Beica, T; Zgura, I

Published: MAR 2007, REVUE ROUMAINE DE CHIMIE, 52, 281, DOI:

X-band ESR spectra of the calamitic and discotic lyotropic nematic phases in sodium dodecyl sulphate (SDS)/decanol/water system, doped with paramagnetic nitroxide free radicals are analyzed in this paper. The studied temperature range was chosen to include phase transitions of the lyotropic systems. The variation of the surfactant hydrocarbon chains ordering versus temperature is determined by the hyperfine splitting tensor (,4) and the spectroscopic splitting tensor ((g) under bar) anisotropies. The temperature dependence of the molecular order parameters for both lyotropic systems and the corresponding angular fluctuations are presented and discussed.

687. Abnormal anti-Stokes Raman spectra of single walled carbon nanotubes raised from coherent anti-Stokes Raman scattering and optical cooling processes

Authors: Baltog, I; Baibarac, M; Mihut, L; Lefrant, S

Published: MAR 2007, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 2, 198, DOI:

For the single-walled carbon nanotubes, the higher values of anti-Stokes/Stokes Raman intensity ratio (I(as)/I(s)) then the predictions of the Maxwell-Bolzmann formula indicates a CARS emission resulting from a wave mixing process between the incident laser light (omega(l)) and Stokes Raman light (omega(s)) generated by a SERS mechanism. The weaker value of (I(as)/Is) observed at resonant excitation of semiconducting nanotubes in the E(22)(S) van Hove state, relates a quantum cooling process occurred during the relaxation of the E22S excited state in two steps-by phonon emission from E(22)(S) to E(11)(S) followed by a spontaneous luminescence emission at E(11)(S).

688. Thermoluminescence and optically stimulated luminescence of gamma-irradiated mineral zircon

Authors: Secu, M; Vainshtein, D; Turkin, A; den Hartog, HW

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673738

Thermoluminescence (TL) manifested by gamma-irradiated mineral zircon has shown a strong TL peak at about 165 degrees C which is due to recombination of electrons and Dy3+ related shallow hole traps. After they have been removed by a short preheat we have observed two TL peaks at 300-320 degrees C and approximate to 420 degrees C, which are mainly due to recombination of electrons and Tb3+ related hole traps centres yielding its characteristic luminescence. The experimental results indicate that optically stimulated luminescence (OSL) is due to luminescent emission of Tb3+ ions and [SiO4](4-) groups. The deep traps related to the 420 degrees C TL peak contribute to the Tb3+ related OSL. The deep traps related to the 300-320 degrees C TL peak contribute to OSL associated with the luminescent emission of [SiO4](4-) groups. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhem.

689. Preliminary study on detection of irradiated foodstuffs from the Romanian market

Authors: Cutrubinis, M; Chirita, D; Savu, D; Secu, CE; Mihai, R; Secu, M; Ponta, C

Published: AUG-SEP 2007, RADIATION PHYSICS AND CHEMISTRY, 76, 1454, DOI: 10.1016/j.radphyschem.2007.02.049

In order to fulfil the European task for market survey in food irradiation the first Romanian laboratory for detection of irradiated foodstuffs was established at IRASM Irradiation Centre. In this preliminary study, a wide range of Romanian food samples (spices, vegetables and meat) gamma irradiated at IRASM have been studied using different detection methods: (1) DNA comet assay, (2) thermoluminescence (TL) and (3) electron spin resonance (ESR) for foodstuffs containing bone or cellulose. The results suggest that there is no general available detection method and there is no perfect detection method. In conclusion, in order to carry out a correct identification of radiation treatment of a food sample it is recommended to use at least two standardised detection methods. (c) 2007 Elsevier Ltd. All rights reserved.

690. High temperature thermolumineseence of BaFCl : EU2+ X-ray storage phosphor

Authors: Secu, CE; Secu, M; Predoi, D

Published: 2007, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 4, NO 3, 4, +, DOI: 10.1002/pssc.200673736

Thermoluminescence (TL) of Eu2+-doped BaFCl polycrystalline powders X- ray irradiated at room temperature show several TL peaks at 364 K, 408 K, 470 K, 524 K and 646 K. Thermally activated recombination processes responsible for TL have been studied using complementary techniques as TL and its bleaching, diffuse reflectance, X-ray excited luminescence (XL) and photostimulated luminescence (PSL). Experimental results indicate that F(Cr) centres are the dominant electron trap centres, the Eu2+-trapped hole aggregate centres playing the role of recombination centres. The 470 K and 646 K TSL glow peaks are assigned to the recombination inside the triple aggregates (Eu2+ - hole centre - F(Cl-) centre). The remaining 408 K and 524 K TL peaks are tentatively assigned to recombination between F centres and double aggregates (Eu2+ - hole centre). (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.