National Institute Of Materials Physics - Romania

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5781 articles found

2451. Luminescent micro- and nanofibers based on novel europium phthalate complex

Authors: Enculescu, M; Preda, N; Matei, E; Enculescu, I

Published: SEP 14 2012, MATERIALS CHEMISTRY AND PHYSICS, 136, 58, DOI: 10.1016/j.matchemphys.2012.06.018

We synthesized by wet chemical route a novel europium-potassium phthalate complex Eu3+K+[(COO)(2)(C6H4)](2). The compound is a white powder insoluble in water. X-ray diffraction evaluation shows that we obtained a new crystalline compound with no traces of the starting materials (potassium hydrogen phthalate and europium chloride). Scanning electron microscopy reveals that the powder consists of fiber-shaped structures with sizes larger than 250 nm in diameter. Energy dispersive X-ray analysis proves that the compound has a 1:1 europium-potassium ratio. Fourier transform infrared spectroscopy confirms the presence of the phthalate in the new compound. Photoluminescence and cathodoluminescence measurements show that the fiber-shaped structures are intensely luminescent with emission bands corresponding to the D-5(0) -> F-7(J) (J = 1-4) Eu (III) ion's transitions in the region between 580 nm and 700 nm, the most intense maximum being observed around 615 nm. Up-converted luminescence with a maximum at 315 nm was recorded. (c) 2012 Elsevier B.V. All rights reserved.

2452. Reversible aggregation between nanoparticles induced by acid-base interactions

Authors: Ionita, G; Ghica, C; Turcu, I; Ionita, P

Published: SEP 12 2012, CHEMICAL PHYSICS LETTERS, 546, 135, DOI: 10.1016/j.cplett.2012.08.009

Acid-base interactions between amino-silica and carboxyl-gold protected nanoparticles, functionalized or not with free stable radicals or fluorescent moieties, were studied by ESR, fluorescence, and TEM. While those nanoparticles are stable in solution, mixing them induces aggregation, due to acid-base interactions; addition of a base or an acid redissolves them. By ESR, strong spin-spin interactions were noticed; by fluorescence, only small differences may be observed, while by TEM, it was noticed that gold nanoparticles are distributed evenly on the surface of the silica nanoparticles. (C) 2012 Elsevier B.V. All rights reserved.

2453. Double layer structure of ZnO thin films deposited by RF-magnetron sputtering on glass substrate

Authors: Besleaga, C; Stan, GE; Galca, AC; Ion, L; Antohe, S

Published: SEP 1 2012, APPLIED SURFACE SCIENCE, 258, 8824, DOI: 10.1016/j.apsusc.2012.05.097

Transparent ZnO films are synthesized by RF-magnetron sputtering (1.78 MHz) onto glass substrates, using a mild-pressed ZnO powder target. The depositions were carried at three inert argon pressures (0.25 Pa, 0.30 Pa, and 0.45 Pa) at two substrate temperatures (100 degrees C and 400 degrees C). The role of the sputtering conditions on ZnO thin films nanostructuring, optical properties and morphology is investigated by Xray diffraction (XRD), X-ray reflectometry (XRR) and Spectroscopic ellipsometry (SE). XRD investigations revealed that ZnO films show a (0 0 l) texture with nanosized crystallites. Right-angle asymmetry of the (0 0 2) diffraction peak is observed. The peak profile analysis using pseudo-Voigt functions unveils a double overlapped peak structure with different coherent zone size values. A double layer structure is evidenced by analyzing the XRR data. Samples prepared at 0.3 Pa at a temperature of 400 degrees C have a similar to 4 nm bottom layer consisting of highly depleted in oxygen ZnO1-x structure, continued by a 53 nm top layer of textured ZnO. Electrical measurements show that the temperature dependence of the conductivity is well described by the Mott variable range hopping (VRH) law. The samples obtained at 400 degrees C have a significantly lower resistivity. (C) 2012 Elsevier B. V. All rights reserved.

2454. Transparent indium zinc oxide thin films used in photovoltaic cells based on polymer blends

Authors: Besleaga, C; Ion, L; Ghenescu, V; Socol, G; Radu, A; Arghir, I; Florica, C; Antohe, S

Published: SEP 1 2012, THIN SOLID FILMS, 520, 6806, DOI: 10.1016/j.tsf.2012.07.030

Indium zinc oxide (IZO) thin films were obtained using pulsed laser deposition. The samples were prepared by ablation of targets with In concentrations, In/(In + Zn), of 80 at.%, at low substrate temperatures under reactive atmosphere. IZO films were used as transparent electrodes in polymer-based -poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1-phenyl-(6,6)C61 1:1 blend - photovoltaic cells. The action spectra measurements revealed that IZO-based photovoltaic structures have performances comparable with those using indium-tin-oxide as transparent electrode. (C) 2012 Elsevier B.V. All rights reserved.

2455. Magnetic pinning effects of epitaxial LaxSr1-xMnO3 nanostructured thin films on YBa2Cu3O7-delta layers

Authors: Petrisor, T; Gabor, MS; Tiusan, C; Galluzzi, V; Celentano, G; Popa, S; Boulle, A; Petrisor, T

Published: SEP 1 2012, JOURNAL OF APPLIED PHYSICS, 112, DOI: 10.1063/1.4748049

The present paper presents the effects of a nanostructured, ferromagnetic La1-xSrxMnO3(LSMO) thin film on the pinning characteristics of an epitaxial YBa2Cu3O7(YBCO) thin film deposited on top. Ordered arrays of LSMO grains were obtained upon growing the film on a terraced (001) SrTiO3 substrate. The analyses of magnetic measurements revealed the presence of a complex vortex pinning mechanism within the YBCO film. With respect to a reference single YBCO layer, an additional pinning potential was observed. Its temperature evolution suggests that a magnetic pinning mechanism is responsible for improved pinning characteristics in the high temperature and field region. Based on the morphology of the underlying LSMO buffer, a strong pinning force is expected to arise due to the anti-dot formations, where a high magnetization gradient exists. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4748049]

2456. The antimicrobial activity of fabricated iron oxide nanoparticles

Authors: Iconaru, SL; Ciobanu, CS; Prodan, AM; Predoi, D

Published: SEP 2012, FEBS JOURNAL, 279, 98, DOI:

2457. Synthesis and characterization of bead-like particles based on chitosan and vinyl polymers

Authors: Preda, N; Enculescu, M

Published: SEP 2012, JOURNAL OF POLYMER RESEARCH, 19, DOI: 10.1007/s10965-012-9963-9

Styrene, methyl methacrylate and glycidyl methacrylate vinyl monomers were grafted onto chitosan by surfactant-free emulsion copolymerization using potassium persulfate as initiator. The grafted compounds were characterized by X-ray diffraction, FTIR spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM) and zeta potential measurements. X-ray diffraction showed changes in the crystallinity pattern of chitosan after the copolymerization reaction. Evidence of grafting was confirmed by FTIR spectroscopy. From zeta potential measurements it is found that the surfaces of graft copolymers latex particles have positive charges resulting from the cationic chitosan molecules. The morphology evaluated by SEM, TEM and AFM proves that in the absence of chitosan, latexes of vinyl homopolymers contain quasi-monodispersed spheres with average diameter of about 400 nm or 250 nm while the graft copolymers latexes are formed by clustered irregular beads with average diameter around 100 nm.

2458. Persistent oscillatory currents in a 1D ring with Rashba and Dresselhaus spin-orbit interactions excited by a terahertz pulse

Authors: Nita, M; Marinescu, DC; Manolescu, A; Ostahie, B; Gudmundsson, V

Published: SEP 2012, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 46, 20, DOI: 10.1016/j.physe.2012.08.017

Persistent, oscillatory charge and spin currents are shown to be driven by a two-component terahertz laser pulse in a one-dimensional mesoscopic ring with Rashba and Dresselhaus spin-orbit interactions (SOI) linear in the electron momentum. The characteristic interference effects result from the opposite precession directions imposed on the electron spin by the two SOI couplings. The time dependence of the currents is obtained by solving numerically the equation of motion for the density operator, which is later employed in calculating statistical averages of quantum operators on few electron eigenstates. The parameterization of the problem is done in terms of the SOI coupling constants and of the phase difference between the two laser components. Our results indicate that the amplitude of the oscillations is controlled by the relative strength of the two SOI's, while their frequency is determined by the difference between the excitation energies of the electron states. Furthermore, the oscillations of the spin current acquire a beating pattern of higher frequency that we associate with the nutation of the electron spin between the quantization axes of the two SOI couplings. This phenomenon disappears at equal SOI strengths, whereby the opposite precessions occur with the same probability. (c) 2012 Elsevier B.V. All rights reserved.

2459. Sn-Doped Hydroxylated MgF2 Catalysts for the Fast and Selective Saccharification of Cellulose to Glucose

Authors: Wuttke, S; Negoi, A; Gheorghe, N; Kuncser, V; Kemnitz, E; Parvulescu, V; Coman, SM

Published: SEP 2012, CHEMSUSCHEM, 5, 1711, DOI: 10.1002/cssc.201200303

2460. The Meyer-Neldel rule in amorphous TiO2 films with different Fe content

Authors: Mardare, D; Yildiz, A; Apetrei, R; Rambu, P; Florea, D; Gheorghe, NG; Macovei, D; Teodorescu, CM; Luca, D

Published: SEP 2012, JOURNAL OF MATERIALS RESEARCH, 27, 2277, DOI: 10.1557/jmr.2012.193

Amorphous titania thin films with increasing Fe content have been prepared by RF magnetron sputtering. X-ray absorption spectroscopy revealed modifications of both local structures/environment of the Ti and Fe atoms, with formation of phases containing amorphous material and a magnetite-like phase. The temperature dependence of the electrical conductivity of the films was investigated for temperatures higher than half of the Debye temperature (T > 391 K). It was found that the electrical conductivity in the amorphous Fe/TiO2 films obeys the Meyer-Neldel rule. The origin of this behavior is explained on the basis of the multiphonon-assisted hopping model.