National Institute Of Materials Physics - Romania

Publications

873 articles found

641. Biocompatibility Studies of Iron-oxide-dextrin Thin Films

Authors: Andronescu, E; Costache, M; Ciobanu, CS; Prodan, AM; Predoi, D

Published: OCT 2010, REVISTA DE CHIMIE, 61, 928, DOI:

Dextrin coated magnetic nanoparticles have been obtained by co-precipitation. As a second step biocompatible magnetic thin film has been synthesized from the iron oxide coated with dextrin powders by pulsed laser deposition technique. Biocompatibility tests consisting of osteoblast cells growth, viability and proliferation were monitored on the surface of the thin films. The cells morphology was characterized by scanning electron microscopy (SEM) after 48h.

642. Structural studies on serum albumins under green light irradiation

Authors: Comorosan, S; Polosan, S; Popescu, I; Ionescu, E; Mitrica, R; Cristache, L; State, AE

Published: OCT 2010, EUROPEAN BIOPHYSICS JOURNAL WITH BIOPHYSICS LETTERS, 39, 1491, DOI: 10.1007/s00249-010-0606-y

This paper presents two new experimental results: the protective effect of green light (GL) on ultraviolet (UV) denaturation of proteins, and the effect of GL on protein macromolecular structures. The protective effect of GL was revealed on two serum albumins, bovine (BSA) and human (HSA), and recorded by electrophoresis, absorption, and circular dichroism spectra. The effect of GL irradiation on protein structure was recorded by using fluorescence spectroscopy and electrophoresis. These new effects were modeled by quantum-chemistry computation using Gaussian 03W, leading to good fit between theoretical and experimental absorption and circular dichroism spectra. A mechanism for these phenomena is suggested, based on a double-photon absorption process. This nonlinear effect may lead to generation of long-lived Rydberg macromolecular systems, capable of long-range interactions. These newly suggested systems, with macroscopic quantum coherence behaviors, may block the UV denaturation processes.

643. Looking for new synthesis of hydroxyapatite doped with europium

Authors: Ciobanu, CS; Andronescu, E; Vasile, BS; Valsangiacom, CM; Ghita, RV; Predoi, D

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1519, DOI:

In this work, we synthesized the properties of bioactive nanocrystalline hydroxyapatite (HAp), Ca-10(PO4)(6)(OH)(2) ceramic powder and nanocrystalline HAp doped with europium (III). The europium doped hydroxyapatite with an atomic ratio Eu/(Eu +Ca) between 2% and 20% were synthesized. The structure, morphology and optical properties were characterized by Xray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FT-IR). The XRD results reveal that the obtained Eu: HAp shows the characteristic peaks of hydroxyapatite in a hexagonal lattice structure. The results indicated that Eu3+ has been successfully doped into the framework of HAp.

644. Dynamics of energy absorption versus crystallization in Bi4Ge3O12 (BGO) amorphous materials

Authors: Polosan, S

Published: OCT 2010, MATERIALS RESEARCH BULLETIN, 45, 1495, DOI: 10.1016/j.materresbull.2010.06.017

Theoretical and experimental determinations show that the intrinsic luminescence of BGO materials is strongly influenced by GeO4- tetrahedra around Bi3+ ions. Besides Bi3+ transitions, the excitonic spectra mask the BGO bandgap. Theoretical computations give the bandgap at 5.19 eV compared with the experimental one at 5.17 eV in BGO crystals and a significant decrease at 3.26 eV in the amorphous materials. This is due to the high disordering of the GeO4- tetrahedral which also reduces the refractive index of the amorphous materials. Formation of excitonic states and their overlap with the Bi3+ transitions suggests that the energy absorption takes place via the p-electrons of the O-2(-) ions and is then transferred to the Bi3+ p-electrons (excited states) close to the conduction band. Light emission appears after de-excitation to the ground state. (C) 2010 Elsevier Ltd. All rights reserved.

645. Synthesis of Eu-doped bismuth germanate nano-ceramic powder

Authors: Polosan, S; Matei, E; Logofatu, C

Published: OCT 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 1508, DOI:

Europium doped Bi(4)Ge(3)O(12) nanocrystals were successfully obtained by solid state reaction between precursor oxides at 800 degrees C. The XRD and XPS measurements shows an increasing of the lattice constant in the case of Eu:BGO nanocrystals, due to the electropositive character of Eu(III) ions compared with the host cations, which induces an ionic character for Eu-O bound and a more covalent one for the Ge-O bounds. The photoluminescence of Eu:BGO due to (5)D(0) -> (7)F(2) transition have a lower splitting compared with Eu:BGO monocrystals suggesting a lower crystal field in the sintered nanocrystals, due to a mixing between the crystalline and amorphous phases.

646. Morphological and optical properties of doped potassium hydrogen phthalate crystals

Authors: Enculescu, M

Published: SEP 1 2010, PHYSICA B-CONDENSED MATTER, 405, 3727, DOI: 10.1016/j.physb.2010.05.074

Potassium hydrogen phthalate (KAP) crystals doped with rhodamine 6G (Rh 6G) and polyvinylpyrrolidone (PVP) were grown by solution evaporation technique. Nucleation occurred without the use of seeds and optically transparent crystals were obtained. The grown crystals were characterized by XRD measurements performed on crystals and their powders, optical transmission and photoluminescence measurements. The influence of the dopants on the structural, morphological and optical properties of the KAP crystals was analysed. Dopants do not change the structure of the single crystals while the addition of PVP changes the morphology of crystals from pseudo-hexagonal to rhomb. Three new XRD reflections are observed in all single-crystal and powder XRD spectra and are probably (0 3 0), (0 4 0) and (0 5 0) lines. The UV cut-off and transparency of the crystals are not changed by doping. Dye-doped KAP crystals exhibit a strong emission band centred at 550 nm excited with 480 nm wavelength. For the dye-doped crystals the up-conversion was investigated and its second harmonic origins are proved using photoluminescence measurements. (C) 2010 Elsevier B.V. All rights reserved.

647. Growth and optical characterization of Pb-, TI-doped LiF crystals

Authors: Somma, F; Montereali, RM; Vincenti, MA; Polosan, S; Secu, M

Published: AUG 2010, OPTICAL MATERIALS, 32, 1312, DOI: 10.1016/j.optmat.2010.04.038

Large and transparent LiF:Pb and LiF:TI crystals were successfully grown by using Kyropoulos method. They were characterized using spectroscopic measurements combined with differential thermal analysis and thermogravimetry (TG) analysis, in order to investigate the effect of dopants upon the optical properties of these crystals. The optical absorption peaks at 278 nm (for Pb) and 273 nm (for TI) have been assigned to the A-type transition of these ions. Photoluminescence spectra have shown bands at 350 nm (for TI) and 375 nm (for Pb), which have been associated to the dopant ions in different configurations in the lattice. (C) 2010 Elsevier B.V. All rights reserved.

648. EFFECTS OF PROTON IRRADIATION ON THE SPECTRAL PERFORMANCE OF PHOTOVOLTAIC CELLS BASED ON CdS/CdTe THIN FILMS

Authors: Ion, L; Enculescu, I; Iftimie, S; Ghenescu, V; Tazlaoanu, C; Besleaga, C; Mitran, TL; Antohe, VA; Gugiu, MM; Antohe, S

Published: AUG 2010, CHALCOGENIDE LETTERS, 7, 530, DOI:

Due to their physical and chemical properties (such as suitable band gaps, large absorption coefficients and good chemical stability) CdTe thin films are interesting for electronic and optoelectronic devices, including particularly photovoltaic cells for space technology. For that specific application, it is of prime importance to study in this type of materials the influence of ionizing radiations on their physical (structural, electrical and optical) properties. In this paper, the photovoltaic cells based on CdS/CdTe thin films, produced by thermal vacuum sublimation, were irradiated with 3 MeV protons at room temperature. The effects of irradiation were studied by investigating the changes in the electrical and optical properties of the cells. It was found that proton irradiation in the above mentioned conditions results mainly in the introduction of defects at the CdS/CdTe interface. A discussion about the possible origin of those defects is given.

649. Synthesis and properties of poly(methyl methacrylate-2-acrylamido-2methylpropane sulfonic acid)/PbS hybrid composite

Authors: Preda, N; Rusen, E; Musuc, A; Enculescu, M; Matei, E; Marculescu, B; Fruth, V; Enculescu, I

Published: AUG 2010, MATERIALS RESEARCH BULLETIN, 45, 1012, DOI: 10.1016/j.materresbull.2010.04.002

The synthesis of a new hybrid composite based on PUS nanoparticles and poly( methyl methacrylate-2acrylamido-2-methylpropane sulfonic acid) [P(MMA-AMPSA)] copolymer is reported. The chemical synthesis consists in two steps: (i) a surfactant-free emulsion copolymerization between methyl methacrylate and 2-acrylamido-2-methylpropane sulfonic acid and (ii) the generation of PbS particles in the presence of the P( MMA-AMPSA) latex, from the reaction between lead nitrate and thiourea. The composite was studied by scanning electron microscopy (SEM), X-ray diffraction, FTIR spectroscopy, thermogravimetric analysis and differential scanning calorimetry. The microstructure observed using SEM proves that the PbS nanoparticles are well dispersed in the copolymer matrix. The X-ray diffraction measurements demonstrate that the PbS nanoparticles have a cubic rock salt structure. It was also found that the inorganic semiconductor nanoparticles improve the thermal stability of the copolymer matrix. (C) 2010 Elsevier Ltd. All rights reserved.

650. Pulsed thermoelectricity

Authors: Apostol, M; Nedelcu, M

Published: JUL 15 2010, JOURNAL OF APPLIED PHYSICS, 108, DOI: 10.1063/1.3456037

A special mechanism of thermoelectric transport is described, consisting of pulses of charge carriers which "fly" periodically through the external circuit from the hot end of the sample to the cold end, with a determined duration of the "on" and "off" times of the electric contacts, while maintaining continuously the thermal contacts. It is shown that such a "resonant" ideal thermogenerator may work cyclically, with the same efficiency quotient as the ideal efficiency quotient of the thermoelectric devices operated in the usual stationary transport regime but the electric flow and power are increased, as a consequence of the concentration of the charge carriers on pulses of small spatial extent. The process is reversible, in the sense that it can be operated either as a thermoelectric generator or as an electrothermal cooler. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3456037]