National Institute Of Materials Physics - Romania

Publications

873 articles found

711. Structural and morphological properties of NiCu magnetic thin films

Authors: Bazavan, D; Bazavan, R; Enculescu, I; Matei, E; Ion, L; Antohe, S

Published: NOV 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 3057, DOI:

NiCu thin films for magnetic applications have been produced by using an electrochemical method. Their structural and morphological properties have been investigated by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM and EDX) and are discussed in correlation with the growth conditions.

712. Phase-change electrical memory elements and devices

Authors: Popescu, M; Lorinczi, A; Sava, F; Velea, A; Matei, E; Socol, G; Mihailescu, IN

Published: OCT 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2621, DOI:

Electrical memory elements based on Ge-Sb-Te pure and doped by Sn-Se have been obtained by pulsed laser deposition on special substrates covered by gold as well as on common glass. A set of electrical memory elements in a 4x4 matrix structure on the glass substrate has been produced. Devices with 3 and 10 memory elements have been constructed and tested for their memory properties. The special features of the voltage-current characteristics have been revealed.

713. Structural and hydrogen absorption/desorption properties of YNi(4-x)Al(x)Mg compounds (with 0 <= x <= 1.5)

Authors: Stan, C; Andronescu, E; Predoi, D; Bobet, JL

Published: AUG 11 2008, JOURNAL OF ALLOYS AND COMPOUNDS, 461, 234, DOI: 10.1016/j.jallcom.2007.07.064

The compounds YNi(4-x)Al(x)Mg with 0 <= x <= 1.5, crystallizing in the C15 structure type (MgCu(4)Sn-type), have been elaborated by mechanical milling and a subsequent heat treatment at 650 degrees C for 1 h. It was possible to synthesize the compounds YNi(4-x)Al(x)Mg with x up to approximately 1.15 and the lattice parameters was in good agreement with those already reported. All the samples, excepting the YNi(4)Mg compound, absorbed and desorbed hydrogen reversibly and no structural change is reported after the hydrogenation. A direct relationship between the lattice parameters and the equilibrium plateau pressure was found. (C) 2007 Elsevier B.V. All rights reserved.

714. Calcium phosphate ceramics for biomedical applications

Authors: Predoi, D; Vatasescu-Balcan, RA; Pasuk, I; Trusca, R; Costache, M

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2155, DOI:

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper describes the synthesis of calcium phosphate ceramics powders via a sol-gel method, The powders were sintered at 600 and 800 degrees C. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDXS) were used for characterization and evaluation of the phase composition, morphology and particle size of samples, The functional group of the coatings were analyzed using Fourier transform infrared (FTIR). The XRD analysis revealed a well crystallized HA structure at both temperatures. At 800 degrees C a small amount of CaO (about 0.4%) was detected. The mean crystallite size, determined from the breadth of the diffraction lines, increases from 30 nm at 600 degrees C to about 110 nm at 800 degrees C. FTIR spectra showed the presence of various PO43- and OH- groups present in the powders. Osteoblast cells were used to determine cell proliferation, viability and citotoxicity after interaction with the prepared bioceramics, by MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a tetrazole) assay. We note that the viability of HAp-600 starts to decrease after 12h, while the viability of HAp-800 decreases after 6h.

715. Optical properties of CaF2 : Eu3+ nanoctystals embedded in transparent oxyfluoride glass ceramic

Authors: Polosan, S; Secu, CE

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2137, DOI:

Transparent oxyfluoride glass ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing CaF2:Eu3+ nanocrystals were produced by annealing of the initial glasses slightly above the CaF2 phase crystallisation peak. The relative good transparency of these materials was due to the small 65 nm, nucleated CaF2 nanocrystallites. X-ray diffraction data have shown an increase of the cell parameters for CaF2:Eu3+ compared with CaF2 which was attributed to the substitution of Ca2+ ions with Eu3+ ions in the CaF2 nanoparticles. Optical investigations using UV-VIS-NIR absorption and luminescence spectroscopy have shown an increase of the splitting of the Eu3+-ion associated luminescences and small shifts of the Eu3+ ion characteristic IR absorption peaks. These effects have been attributed to the Eu3+ environment evolving from the glass to the crystalline-like one.

716. Transport through quantum dots with magnetic impurities

Authors: Tolea, M; Aldea, A; Bulka, BR

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1758, DOI:

We analyze the electronic transport through a quantum dot that contains a magnetic impurity. The coherent transport of electrons is governed by the quantum confinement inside the dot, but is also influenced by the exchange interaction with the impurity. The interplay between the two gives raise to the singlet-triplet splitting of the energy levels available for the tunneling electron. In this paper, we focus on the charge fluctuations and, more precisely, the height of the conductance peaks. We show that the conductance peaks corresponding to the triplet levels are three times higher than those corresponding to singlet levels, if electronic correlations are neglected (for non-interacting dots, when an exact solution can be obtained). Next, we consider the Coulomb repulsion and the many-body correlations. In this case, the singlet/triplet peak height ratio has a complex behavior. Usually the highest peak corresponds to the state that is lowest in energy (ground state), regardless if it is singlet or triplet. In the end, we get an insight on the Kondo regime for such a system, and show the formation of three Kondo peaks. We use the equation of motion method with appropriate decoupling.

717. Resonant Raman scattering and absorption spectroscopy studies on individual carbon nanotubes in surfactant solutions

Authors: Husanu, M; Baibarac, M; Preda, N; Baltog, I

Published: JUL 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1726, DOI:

Carbon Nanotubes are exotic low-dimensional systems, and due to their remarkable properties, are promising components for technological applications. The electronic and vibrational signatures raising from their existence as individual entities or associated in bundles, is still a controversed subject. A careful analysis of the G (similar to 1600 cm(-1)) and RBM (100-200 cm(-1)) band features as: profile, peak position and intensity in the Raman spectra may be a valuable indication about their dispersion state. The UV-VIS-NIR absorption spectrum comes to support this assumption. Observing the absorption spectra associated to resonant excitation of semiconducting and metallic nanotubes, may reveal complementary informations concerning the individualization procedure efficiency.

718. Potassium hydrogen phthalate (KAP) micro- and nano-rods prepared by a template approach

Authors: Enculescu, M

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1504, DOI:

Micro and nanorods of potassium acid phthalate (KAP) with diameters ranging from a hundred nanometers to tens of microns were obtained by solution growth in polycarbonate (PC) ion track templates. The ion track templates were produced by swift heavy ion irradiation of PC foils (e.g. U with 11.4 MeV/nucleon specific energy) and subsequently etching. After the growth the host templates were partially dissolved in dichlormethane and imagined by scanning electron microscopy. The template approach allows the fabrication of arrays of uniform nanostructures with a controlled morphology.

719. Study of osteoblast interaction with iron oxide nanoparticles coated with dextrin in cell culture

Authors: Vatasescu-Balcan, RA; Predoi, D; Costache, M

Published: JUN 2008, FEBS JOURNAL, 275, 374, DOI:

720. Transport properties of electrodeposited ZnO nanowires

Authors: Tazlaoanu, C; Ion, L; Enculescu, I; Sima, M; Enculescu, M; Matei, E; Neumann, R; Bazavan, R; Bazavan, D; Antohe, S

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2507, DOI: 10.1016/j.physe.2007.07.013

ZnO nanowires were electrodeposited by using a template approach. Ion track polycarbonate foils (30 mu m thick) were used as templates. Current-voltage (I-V) characteristics were recorded in the temperature range 40-300 K. I-V characteristics show a symmetric, non-linear shape, at temperatures greater than 240 K and voltages greater than 15 V. At lower temperatures, linear characteristics were recorded for the voltage range used. The temperature dependence of the electrical resistance is activated, with activation energy of 0.42 eV at temperatures greater than 240 K. (C) 2007 Elsevier B.V. All rights reserved.