National Institute Of Materials Physics - Romania

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860 articles found

421. Spark plasma sintered MgB2 co-added with c-BN and C-60

Authors: Ionescu, AM; Aldica, G; Popa, S; Enculescu, M; Sandu, V; Pasuk, I; Kuncser, A; Miu, L; Badica, P

Published: FEB 15 2016, MATERIALS CHEMISTRY AND PHYSICS, 170, 209, DOI: 10.1016/j.matchemphys.2015.12.040

High density (above 92%) superconducting bulks of MgB2 co-added with cubic BN (c-BN) and fullerenes (C-60) were obtained by the ex-situ spark plasma sintering (SPS). Compositions were (MgB2)((1-x))(C)(x)(c-BN)(0.01), x = 0.0125, 0.025, 0.05, 0.075. The co-added sample (MgB2)(0.975)(C)(0.025)(c-BN)(0.01) shows a marginally higher critical current density J(c) at intermediate magnetic fields and below 15 K than for optimum samples added with c-BN or C-60. For this sample, pinning is in the point pinning limit and the delta T-c mechanism is dominant. At high magnetic fields co-added samples are inferior to samples added with one additive, but are superior to pristine sample. Co-addition of c-BN and C-60 is not effective for vortex pinning when compared with individual addition. The result is discussed based on phase formation aspects, microstructural details and residual strain. It was found that in the presence of C-60, c-BN consumption with formation of MgNB9 is intensified with implications on different elements that influence pinning. (C) 2015 Elsevier B.V. All rights reserved.

422. Non-volatile memory devices based on Ge nanocrystals

Authors: Vasilache, D; Cismaru, A; Dragoman, M; Stavarache, I; Palade, C; Lepadatu, AM; Ciurea, ML

Published: FEB 2016, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 213, 259, DOI: 10.1002/pssa.201532376

The article presents the fabrication and characterization of NV (non-volatile) memory devices based on SiO2/Ge/SiO2 trilayer structures on Si wafers. The trilayer structures were obtained by using the magnetron sputtering method for the deposition of gate SiO2 and intermediate Ge layers and the rapid thermal oxidation for the growth of tunnel SiO2 layer. Rapid thermal annealing was performed for obtaining Ge nanocrystals embedded in the SiO2 gate oxide, as charge-storage elements. Two NV cross bar memory structures based on two cell sizes of 300x300 and 100x100m(2) were manufactured. Capacity-voltage curves were measured on the memory devices, at different frequencies in the 1kHz-10MHz range at room temperature (RT) for evidencing the hysteresis loops and for showing that the devices keep memory in time at these frequencies. We have obtained capacity-voltage hysteresis curves with large memory window up to 2V. We demonstrate that the trilayer structure SiO2/Ge/SiO2/on Si with Ge NCs embedded in the SiO2 gate oxide is suitable for NV memory applications having a large number of cells.

423. Exploring porous nanosilica-TEMPO as heterogeneous aerobic oxidation catalyst: the influence of supported gold clusters

Authors: Shakir, AJ; Florea, M; Culita, DC; Ionita, G; Ghica, C; Stavarache, C; Hanganu, A; Ionita, P

Published: FEB 2016, JOURNAL OF POROUS MATERIALS, 23, 254, DOI: 10.1007/s10934-015-0076-9

TEMPO stable free radical has been supported on porous silica nanoparticles in different ways and the resulted materials have been tested as heterogeneous oxidation catalyst of three benzylic alcohols using air as final oxidant and nitrosonium tetrafluoroborate as cocatalyst. Good to excellent yields were obtained. The catalytic system consists in fact in two coupled cycles, NO/NO2 and TEMPO+/TEMPO, able to convert under mild conditions (room temperature, air, metal and halogen free condition) alcohols into aldehydes or ketones. Under these conditions, supported TEMPO on silica nanoparticles containing gold clusters lowers the efficiency of the catalyst.

424. AMMONIA SENSING WITH 5 MOL% LANTHANUM DOPED BARIUM STRONTIUM TITANATE UNDER HUMID AIR BACKGROUND

Authors: Simion, CE; Stanoiu, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Vasile, E; Vasile, E; Tudor, IA

Published: FEB 2016, REVUE ROUMAINE DE CHIMIE, 61, +, DOI:

Nanostructured Ba0.7Sr0.3TiO3 (BST) with 5 molar % of Lanthanum (La) have been synthesized using a high pressure hydrothermal chemical route. The structural and morphological investigations were performed. Termogravimetry/differential scanning calorimetry and Raman investigations have been also employed to analyse the as-prepared material. The gas sensing investigations have indicated the ability of La doped BST to detect ammonia, when operated at room temperature in humid background. The obtained results were discussed with respect to the possible gas-sill-face interaction mechanism. In addition, the said material showed low cross-sensitivity to other possible interfering gases: methane, carbon monoxide, nitrogen dioxide, sulphur dioxide and hydrogen sulphide.

425. Study of GeSn based heterostructures: towards optimized group IV MQW LEDs

Authors: Stange, D; von den Driesch, N; Rainko, D; Schulte-Braucks, C; Wirths, S; Mussler, G; Tiedemann, AT; Stoica, T; Hartmann, JM; Ikonic, Z; Mantl, S; Grutzmacher, D; Buca, D

Published: JAN 25 2016, OPTICS EXPRESS, 24, 1367, DOI: 10.1364/OE.24.001358

We present results on CVD growth and electro-optical characterization of Ge0.92Sn0.08/Ge p-i-n heterostructure diodes. The suitability of Ge as barriers for direct bandgap GeSn active layers in different LED geometries, such as double heterostructures and multi quantum wells is discussed based on electroluminescence data. Theoretical calculations by effective mass and 6 band k center dot p method reveal low barrier heights for this specific structure. Best configurations offer only a maximum barrier height for electrons of about 40 meV at the Gamma point at room temperature (e.g. 300 K), evidently insufficient for proper light emitting devices. An alternative solution using SiGeSn as barrier material is introduced, which provides appropriate band alignment for both electrons and holes resulting in efficient confinement in direct bandgap GeSn wells. Finally, epitaxial growth of such a complete SiGeSn/GeSn/SiGeSn double heterostructure including doping is shown. (C)2016 Optical Society of America

426. Multiscale investigation of USPIO nanoparticles in atherosclerotic plaques and their catabolism and storage in vivo

Authors: Maraloiu, VA; Appaix, F; Broisat, A; Le Guellec, D; Teodorescu, VS; Ghezzi, C; van der Sanden, B; Blanchin, MG

Published: JAN 2016, NANOMEDICINE-NANOTECHNOLOGY BIOLOGY AND MEDICINE, 12, 200, DOI: 10.1016/j.nano.2015.08.005

The storage and catabolism of Ultrasmall SuperParamagnetic Iron Oxide (USPIO) nanoparticles were analyzed through a multiscale approach combining Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM) at different times after intravenous injection in an atherosclerotic ApoE(-/-) mouse model. The atherosclerotic plaque features and the USPIO heterogeneous biodistribution were revealed down from organ's scale to subcellular level. The biotransformation of the nanoparticle iron oxide (maghemite) core into ferritin, the non-toxic form of iron storage, was demonstrated for the first time ex vivo in atherosclerotic plaques as well as in spleen, the iron storage organ. These results rely on an innovative spatial and structural investigation of USPIO's catabolism in cellular phagolysosomes. This study showed that these nanoparticles were stored as non-toxic iron compounds: maghemite oxide or ferritin, which is promising for MRI detection of atherosclerotic plaques in clinics using these USPIOs. From the Clinical Editor: Advance in nanotechnology has brought new contrast agents for clinical imaging. In this article, the authors investigated the use and biotransformation of Ultrasmall Super-paramagnetic Iron Oxide (USPIO) nanoparticles for analysis of atherosclerotic plagues in Two Photon Laser Scanning Microscopy (TPLSM) and High-Resolution Transmission Electron Microscopy (HRTEM). The biophysical data generated from this study could enable the possible use of these nanoparticles for the benefits of clinical patients. (C) 2015 Elsevier Inc. All rights reserved.

427. Dielectric characterization of BaxSr1-xFe12O19 (x=0.05-0.35) ceramics

Authors: Cernea, M; Negrea, RF; Ciuchi, IV; Baldisserri, C; Trusca, R; Galassi, C

Published: JAN 2016, CERAMICS INTERNATIONAL, 42, 1056, DOI: 10.1016/j.ceramint.2015.09.029

BaxSr1-xFe12O19 (x=0.05, 0.15, 0.25, 0.35) ferrites were prepared by both the sol gel and conventional solid state reaction techniques. The structural characteristics and dielectric properties of these ferrites were investigated and compared. BaxSr1-xFe12O19 ceramics obtained by the sol gel method show homogeneous morphology and single crystalline phase while those prepared by solid state reaction route exhibit less homogeneous morphology, being accompanied by a secondary crystalline phase (BaFe2O4). The size of the grains varies in the range 200-300 nm for x=0.05-0.35 when the powders are prepared by sol gel method and, 600-700 nm for the powders prepared by solid state reaction. For the same value of x, the BaxSr1-xFe12O19 ferrites obtained via sol-gel display higher permittivity and lower dielectric losses compared to those prepared by solid state reaction route. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

428. LTCC-based Ceramic Microsystems with Integrated Fluidic Elements and Sensors

Authors: Belavic, D; Hodnik, M; Santo, M; Bolado, P; Ursic, H; Bradesko, A; Malic, B; Mercioniu, IF; Bencan, A; Makarovic, K; Ciobanu, RC; Schreiner, C

Published: 2016, PROCEEDINGS OF THE 2016 INTERNATIONAL CONFERENCE AND EXPOSITION ON ELECTRICAL AND POWER ENGINEERING (EPE 2016), 46, DOI: 10.1109/ICEPE.2016.7781299

In this contribution the design and fabrication of ceramic microsystems with integrated different microfluidic elements and sensors will be presented. Ceramic microsystems are based on unconventional application of low-temperature co-fired ceramic technology and materials. This unconventional application is related to three-dimensional ceramic structures, such as cantilevers, ledges, bridges, diaphragms, valleys, channels, holes and cavities, valves, mixers, diffusors, distributors, collectors, flow limiters, sensors, and actuators.

429. INVESTIGATIONS ON THE PROPERTIES OF A TWO-DIMENSIONAL NANOPATTERNED METALLIC FILM

Authors: Breazu, C; Preda, N; Socol, M; Stanculescu, F; Matei, E; Stavarache, I; Iordache, G; Girtan, M; Rasoga, O; Stanculescu, A

Published: OCT-DEC 2016, Digest Journal of Nanomaterials and Biostructures, 11, 1229, DOI:

This paper presents some investigations of the effect of nanopatterning on the properties of aluminum layer deposited by sputtering. UV-Nanoimprint Lithography technique has been used for the realization of a 2D array of nanostructures (pillars) in aluminum film characterized by cylindrical shape and the following structural parameters: diameter between 400 nm and 490 nm, depth between 320 nm and 420 nm and periodicity of 1.1 mu m, which have been revealed by SEM and AFM measurements. The UV-Vis transmission, reflection and photoluminescence measurements have evidenced the effect of the nanopatterning on the optical properties of the A1 layer.

430. MOSSBAUER AND MAGNETIC INVESTIGATION OF IRON NITRIDE WITH MARTENSITE STRUCTURE SYNTHESISED FROM OXY-HYDROXIDE TYPE PRECURSOR

Authors: Palade, P; Plapcianu, C; Mercioniu, I; Comanescu, CC; Schinteie, G

Published: JAN-MAR 2016, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 11, 63, DOI:

Fe16N2 fine particles were prepared by reduction in 5% H-2/Ar gas mixture flow, starting from goethite or hematite precursors, followed by nitridation in ammonia gas flow. Small amounts of metallic iron and iron oxide are present besides the main phase which is an ordered iron nitride having martensite structure (alpha''-Fe16N2) as revealed by Mossbauer spectroscopy measurements. However, X-ray diffraction data do not show any traces of oxides due to their high degree of amorphization. When nitridation is performed at about 150 C-0, Fe4N phase begins to form and its presence deteriorates the magnetic properties. The samples prepared by nitridation of goethite present better magnetic properties compared to those obtained by nitridation of hematite. Magnetic and Mossbauer measurements performed at ambient temperature were corroborated in order to extract the magnetization at saturation value for each phase which occurs in the obtained samples. The corresponding values are 226 emu/g for Fe16N2 and 198 emu/g for metallic iron contained in the prepared powders.