National Institute Of Materials Physics - Romania

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5781 articles found

2821. Spark plasma sintering studies of nanosize lanthanide-doped ceria obtained by sot-gel method

Authors: Plapcianu, C; Valsangiacom, C; Schaffer, JE; Wieg, A; Garay, J; Stanciu, L

Published: SEP-OCT 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1108, DOI:

Doped ceria powders, Ce-0.8 Ln(0.2)O(2-x) (Ln = Gd3+, Sm3+ and Yb3+) were sintered to nearly full density by Spark Plasma Sintering at 1100 and 1200 degrees C. The starting powders were obtained via a sol-gel method and had nanometric dimensions: 26.4 nm (Gd), 19.3 nm (Sm) and 31.4 nm (Yb). Samples characterization was performed by SEM, TEM and XRD to determine their structural and microstructural characteristics. The ionic conductivities of the sintered samples were determined by impedance measurements. The influence of the chemical composition, sintering temperature and microstructural characteristics on the total ionic conductivity were evaluated and discussed.

2822. BIOCOMPATIBILITY STUDY OF EUROPIUM DOPED CRYSTALLINE HYDROXYAPATITE BIOCERAMICS

Authors: Ciobanu, CS; Massuyeau, F; Andronescu, E; Stan, MS; Dinischiotu, A; Predoi, D

Published: OCT-DEC 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 1647, DOI:

For the first time we presented the preliminary results of biocompatibility studies on bioceramic hydroxyapatite powders doped with europium Ca10-xEux(PO4)(6)(OH)(2), with 0.01 <= x(Eu) <= 0.2 prepared at low temperature by a simple coprecipitation approach. The X-ray diffraction (XRD) studies revealed the characteristic peaks of hydroxyapatite in each sample. No evidence for additional crystalline phases was found, proving the complete substitution of Eu in the HAp lattice in the whole range of concentrations. The scanning electron microscopy (SEM) observations suggest that these materials present a little different morphology, which reveals a homogeneous aspect of the synthesized particles for all samples. The PL investigations shown the PL intensity changed considerably by varying the x(Eu). The value of x(Eu) in the hydroxyapatite formula has almost no effect on the wavelength of emission peaks. In order to test Hap_Eu biocompatibility, the effect of europium substituted hydroxyapatite nanocristalline powders with different x(Eu) on cell viability and proliferation of HEK293 cell line were evaluated. The in vitro investigation showed no significant decrease of viability of HEK293 cell line and low levels of intracellular lipid peroxidation in the Hap_Eu treated cells. In conclusion, the results suggest that Eu doped HAp has low toxicity and exhibit a good biocompatibility.

2823. Photoluminescence of poly (N vinylcarbazole)/carbon nanotubes composites

Authors: Gontia, II; Baibarac, M; Baltog, I

Published: MAY-JUN 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 582, DOI:

The photoluminescence (PL) of two types of poly (N-vinyl-carbazole)(PVK)/carbon nanotubes (CN) composites, prepared by chemical and electrochemical method, has been investigated. In comparison with the pure PVK, the chemically prepared PVK/NC sample shows a significant PL quenching and a shorter decay time. For the samples prepared electrochemically, PL increases in intensity, red shifts and gets longer decay time with the increase of voltammetric cycles number. In addition, the latter shows a change in emission from high-energy excimer to low-energy excimer after a treatment with NH(4)OH.

2824. DEPENDENCE OF OPTICAL RESPONSE ON pH OF A WATER-SOLUBLE Zn(II)-METALLOPORPHYRIN

Authors: Fagadar-Cosma, E; Creanga, I; Maranescu, B; Palade, A; Lorinczi, A; Fagadar-Cosma, G; Popescu, M

Published: JAN-MAR 2011, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 6, 80, DOI:

Nowadays, porphyrin derivatives are extensively used as analytical reagents. This work put the basis for a rapid, simple and inexpensive method developed for pH determination. It was demonstrated the potential for a water soluble metalloporphyrin, 5,10,15,20-tetrakis(N-methyl-4-pyridyl) porphyrin-Zn(II) tetrachloride (Zn-TNMPyP) to be a potential optical pH sensor in the 5.5-10.5 domain. Monitoring of the variations in the absorption spectra of the Zn-TNMPyP, both regarding the Soret and the Q(0,1) band, generated by the exposure to different base concentrations allowed us to notice the linearity of the response at different pH values.

2825. Structural and electrical properties of ceramic composite 10Y(2)O(3):CeO2+(10%)(150ppm)Y2O3:alpha-Al2O3

Authors: Ionascu, AM; Mercioniu, I; Notingher, PV; Popescu-Pogrion, N

Published: 2011, 2011 7TH INTERNATIONAL SYMPOSIUM ON ADVANCED TOPICS IN ELECTRICAL ENGINEERING (ATEE), DOI:

The attractive properties of Yttria doped ceria, particularly the structural and material properties, have led to vast research efforts to investigate and develop such materials. One of the main applications of this ceramic is in the solid oxides fuel cells for intermediate temperatures IT-SOFC. The aim of this paper is the preparation and characterization of Y doped Ceria - low Y doped alpha-Al2O3, a new composite for IT-SOFC. (10 mol %) Y : CeO2 and (150 ppm) Y : alpha - Al2O3 - composite were obtained by sol-gel or mechanical route for 10YSC, mechanical route for 150 Y : alpha - Al2O3. Grain shapes, grain size distributions and the mean grain value were determined by SEM, EDX and statistical investigations.

2826. SYNTHESIS AND PRELIMINARY CHARACTERIZATION OF ERBIUM LITHIUM NIOBIUM GALLIUM GARNET

Authors: Toma, O; Gheorghe, L; Vlaicu, AM

Published: 2011, ROMANIAN JOURNAL OF PHYSICS, 56, 934, DOI:

The synthesis of a new garnet, Er3Li0.275Nb0.275Ga4.45O12 (ErLNGG), by solid-state reaction, is reported. A comparison of the fluorescence spectra of Er3+ in ErLNGG and in Er-doped (5 at. %) Calcium Lithium Niobium Gallium Garnet (CLNGG) suggests an ordering of the partially disordered CLNGG when Ca2+ ions are completely substituted by Er3+ ions.

2827. Experimental configuration for the simultaneous study of magnetization reversal and giant magnetoresitance effects in exchange coupled spin valve structures

Authors: Schinteie, G; Kuncser, C; Kuncser, A; Iofciu, F; Jepu, I; Antohe, S

Published: SEP-OCT 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1094, DOI:

A designed experimental configuration for the simultaneous study of magnetization reversal and giant magnetoresistance effects in layered systems is reported. The suitability of the device, designed mainly for didactical purposes, to prove giant magneto-resistance effects is exemplified in case of exchange coupled spin valve structures. The multilayer structures were prepared by theromo-ionic vacuum arc methods and initially characterized by X-ray diffractometry and energy dispersive Xray spectroscopy. According to the performed experiments, it has been clearly proven the presence of magnetoresistance maxima ever ranges of applied fields inducing antiparallel magnetizations of the two ferromagnetic layers interfacing a thin conductive layer.

2828. Influence of defects on the switching speed of Ge2Sb2Te5

Authors: Velea, A; Popescu, M; Lorinczi, A; Sava, F; Simandan, ID; Mihai, C

Published: NOV-DEC 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 1596, DOI:

Chalcogenide phase change materials are one of the major contenders for the new non-volatile memory applications. Here is reported that the switching speed of Ge2Sb2Te5 is strongly dependent on the percent of defects in the material. Using cellular automata simulations it was shown that the size of the percolation cluster is minimum, thus the switching speed is maximum, for a percent of around 25% defects in the material. This is a property of the Ge2Sb2Te5 that can be useful for new phase change materials and devices design with better switching properties.

2829. Current enhancement and negative differential conductance in parallel quantum dot systems

Authors: Tanatar, B; Moldoveanu, V

Published: 2011, PHYSICS OF SEMICONDUCTORS: 30TH INTERNATIONAL CONFERENCE ON THE PHYSICS OF SEMICONDUCTORS, 1399, DOI: 10.1063/1.3666366

We present calculations on the transport properties of a double quantum dot (DQD) capacitively coupled to another individually biased dot. The effects of the intradot and interdot Coulomb interaction are included within the random-phase approximation (RPA) implemented in the Keldysh formalism. We show that by increasing the bias on the nearby dot the inelastic Coulomb scattering modifies the current in the double dot. The sign of the current depends on the detuning of the double dot levels and intradot transitions lead to negative differential conductance. The enhancement of the current due to the energy quanta transferred from the strongly biased dot suggests a quantum ratchet or Coulomb drag mechanism.

2830. Sn-119- AND Fe-57- MOSSBAUER INVESTIGATION OF xSnO(2)-[(1-X)[alpha-Fe2O3] NANOPARTICLE SYSTEM. (I) MAGNETIC HYPERFINE FIELD DISTRIBUTION IN Sn-LOW DILUTE SYSTEM

Authors: Constantinescu, S; Diamandescu, L; Bibicu, I; Tarabasanu-Mihaila, D; Feder, M

Published: 2011, ROMANIAN JOURNAL OF PHYSICS, 56, 707, DOI:

A series of xSnO(2)-(1-x)alpha-Fe2O3 (x=0.0-1.0) was prepared by a hydrothermal route starting with an aqueous mixture of iron (III) chloride hexahydrate, FeCl3 center dot 6H(2)O, and tin (IV) chloride pentahydrate, SnCl4 center dot 5H(2)O. The as resulted nanoscaled powders have been investigated by X-ray diffraction (XRD) and Sn-119 Mossbauer spectroscopy in transmission geometry and conversion electron. Under x = 0.300, the spectra reveal the appearance of magnetic hyperfine induced structure. At x = 0.300, the spectrum shows a magnetic phase (M) with the percentage of about 17%. The appearance of hyperfine magnetic fields suggests the location of the nonmagnetic Sn4+ ions, surrounded by the Fe3+ ions, in the interstitial and substitutional sites of alpha-Fe2O3 phase. On the other hand, the dependence of the total spectrum areas, vs. molar concentration x, displays a jump around x similar to 0.45, suggesting a change of the characteristic Debye temperature in the Mossbauer factor. The reported spectra have been fitted and the obtained hyperfine parameters are discussed in terms of reduced dimensional effects, super-transferred hyperfine interactions (STHI) and magnetic hyperfine field distribution (MHFD).