National Institute Of Materials Physics - Romania

Publications

5914 articles found

4171. The influence of neutron irradiation on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz superconducting phase: The role of the grain edge

Authors: Mihalache, V; Totovana, A; Sandu, V; Popa, S; Aldica, G; Iyo, A

Published: AUG 2005, JOURNAL OF SUPERCONDUCTIVITY, 18, 467, DOI: 10.1007/s10948-005-0029-7

Using the transport and magnetization measurements, the influence of neutron irradiation at a fluence of 5 x 10(17) n cm(-2) on (B0.65C0.35)Ba1.4Sr0.6Ca2Cu3Oz has been investigated. The neutron irradiation was found to decrease critical temperature and transport critical current density, increase the residual and normal state resistivity, and improve the intragranular critical current density with 1.6 x 10(5) A/cm(2) (at 77.3 K and in the applied field up to 160 kA m) and Delta M-irr/Delta M-nonirr ratio (up to factor of 3) at highest field used for investigation. The field dependence of this ratio, which is below the unity at very low field but higher than I at high fields, correlated with the shape of the hysteretic loops as well as with the change of the transport parameters after irradiation suggests the role of the irradiation-induced effects on the grain edges. We discuss these effects in the framework of the Bean-Livingstone surface barriers and geometrical barriers.

4172. Surface-enhanced Raman scattering, photoluminescence and viscosity studies on C-60 aggregates in N-metryl-2-pyrrolidinone

Authors: Baltog, I; Mihut, L; Baibarac, M; Preda, N; Velula, T; Lefrant, S

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2172, DOI:

Correlated studies of Surface Enhanced Raman Scattering (SERS) spectroscopy, photoluminescence (PL) and viscosity on aggregation of C-60 fullerene in N-methyl-2-pyrrolidinone (NMP) solutions were performed. The aggregation is a result of storing of the solutions at the room temperature for different periods of time. The modified phonon spectrum in the aggregate phase is a consequence of the intermolecular interactions that lead to a large reduction in parent I-h C-60 symmetry. The Raman range below 800 cm(-1) is the most diagnostic for aggregate assignment. Substitution of the original of H, (1) band from similar to 269 cm(-1) with a new one at similar to 255 cm(-1) relates the formation of (C-60, NMP) complexes. In the second stage of aggregation, this band shifts at similar to 246 cm(-1) and a new band, associate to the interball interaction, is formed at similar to 94 cm(-1). PL emission of the C-60 solutes in NMP presents two components, one in red (1.92-2.00 eV) and another in green (2.18-2.3 eV), which originate in two successive processes. Their weights depend on C-60 concentration and on storage time. In the beginning are formed quickly molecular complexes (C-60, NMP) by charge transfer, which on associate slowly in stable aggregates. A dependence of specific viscosity on C-60 solution concentration is observed too.

4173. Peculiar orientation of nematic liquid crystals on rubbed polyvinylimidazole

Authors: Frunza, S; Beica, T; Moldovan, R; Zgura, I; Frunza, L

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2157, DOI:

Alignment properties of rubbed films of polyvinyl imidazole were studied by observing with the polarizing microscope the features of the nematic liquid crystal (LC) droplets onto these layers. It was found that the observing of the droplets can reveal the direction of easy axis on the alignment substrate not only in the case of LC having the director normal to the LC/air interface but also in the case of the director tangent to this interface, when no disclination line could be seen. We observed that some of the LCs are oriented parallel to the rubbing direction, but the other LCs are perpendicularly oriented. This peculiar behavior is at variance to that found on rubbed layers of polyvinyl alcohol. The role of the end-groups in the structure of the LCs on the alignment properties is discussed.

4174. Properties of ZnO thin films prepared by radio-frequency plasma beam assisted laser ablation

Authors: Scarisoreanu, N; Matei, DG; Dinescu, G; Epurescu, G; Ghica, C; Nistor, LC; Dinescu, M

Published: JUL 15 2005, APPLIED SURFACE SCIENCE, 247, 525, DOI: 10.1016/j.apsusc.2005.01.140

Zinc oxide thin films were obtained by laser ablation of a Zn target in oxygen reactive atmosphere, the oxygen being supplied either by a standard gas inlet valve or from a radio-frequency (rf) oxygen plasma. Pt-coated silicon and MgO were used as substrates. The influence of the deposition parameters as laser wavelength (266, 355, 1064 nm), laser fluence (1.5-20 J/cm(2)) and oxygen pressure (1-60 Pa) was studied. The influence of the rf plasma beam addition on the morphological proprieties of zinc oxide films was particularly investigated, simultaneously with several configurations of the direction of the ablation plasma, the rf plasma beam and the substrate. The obtained films, with thicknesses in the range of 50 nm to 1 mu m have been characterized by atomic force microscopy (AFM), X-ray diffraction (XRD), transmission electron microscopy (TEM). (c) 2005 Elsevier B.V. All rights reserved.

4175. Pulsed laser deposition of thin films of various full Heusler alloys CO2MnX (X = Si, Ga, Ge, Sn, SbSn) at moderate temperature

Authors: Valerio, E; Grigorescu, C; Manea, SA; Guinneton, F; Branford, WR; Autric, M

Published: JUL 15 2005, APPLIED SURFACE SCIENCE, 247, 156, DOI: 10.1016/j.apsusc.2005.01.079

This work presents pulsed laser deposition of cobalt-based Hensler thin films Co2MnX (X = Si, Ga, Ge, Sn, SbSn) on different substrates (Si, GaAs, InAs). The deposition processes developed in vacuum (about 10(-5) Pa) to avoid oxidation of the films and targets. The temperature of the substrates during the depositions was kept below 500 K to minimise interface interdiffusion. From X-ray diffraction, we found that the films are crystalline and slightly oriented. The stoichiometric composition of the films was further checked by EDS, while the size and density of droplets were determined by SEM. The magnetic properties of the films are consistent with those of the bulk material used as target. (c) 2005 Elsevier B.V. All rights reserved.

4176. (Zr, Sn)TiO4 thin films for application in electronics

Authors: Nistor, M; Gherendi, F; Magureanu, M; Mandache, NB; Ioachim, A; Banciu, MG; Nedelcu, L; Popescu, M; Sava, F; Alexandru, HV

Published: JUL 15 2005, APPLIED SURFACE SCIENCE, 247, 174, DOI: 10.1016/j.apsusc.2005.01.124

Thin films of zirconium tin titanate, (Zr0.8Sn0.2)TiO4 (ZST) were deposited using a pulsed electron beam source based on a channel-spark discharge for target ablation. An advanced degree of crystallization was obtained for the films deposited on alumina substrate post-annealed at 1000 degrees C. The crystalline lattice constants of the films are very close to those of the target material, which confirms the same stoichiometry in ZST films and in the bulk. (c) 2005 Elsevier B.V. All rights reserved.

4177. Development of radiation tolerant semiconductor detectors for the Super-LHC

Authors: Moll, M; Adey, J; Al-Ajili, A; Alfieri, G; Allport, PP; Artuso, M; Assouak, S; Avset, BS; Barabash, L; Barcz, A; Bates, R; Biagi, SF; Bilei, GM; Bisello, D; Blue, A; Blumenau, A; Boisvert, V; Bolla, G; Bondarenko, G; Borchi, E; Borrello, L; Bortoletto, D; Boscardin, M; Bosisio, L; Bowcock, TJV; Brodbeck, TJ; Broz, J; Bruzzi, M; Brzozowski, A; Buda, M; Buhmann, P; Buttar, C; Campabadal, F; Campbell, D; Candelori, A; Casse, G; Cavallini, A; Charron, S; Chilingarov, A; Chren, D; Cindro, V; Collins, P; Coluccia, R; Contarato, D; Coutinho, J; Creanza, D; Cunningham, W; Dalla Betta, GF; Dawson, I; de Boer, W; De Palma, M; Demina, R; Dervan, P; Dittongo, S; Dolezal, Z; Dolgolenko, A; Eberlein, T; Eremin, V; Fall, C; Fasolo, F; Fizzotti, F; Fleta, C; Focardi, E; Forton, E; Fretwurst, E; Garcia, C; Garcia-Navarro, JE; Gaubas, E; Genest, MH; Gill, KA; Giolo, K; Glaser, M; Goessling, C; Golovine, V; Sevilla, SG; Gorelov, I; Goss, J; Bates, AG; Gregoire, G; Gregori, P; Grigoriev, E; Grillo, AA; Groza, A; Guskov, J; Haddad, L; Harkonen, J; Hauler, F; Hoeferkamp, M; Honniger, F; Horazdovsky, T; Horisberger, R; Horn, M; Houdayer, A; Hourahine, B; Hughes, G; Ilyashenko, I; Irmscher, K; Ivanov, A; Jarasiunas, K; Johansen, KMH; Jones, BK; Jones, R; Joram, C; Jungermann, L; Kalinina, E; Kaminski, P; Karpenko, A; Karpov, A; Kazlauskiene, V; Kazukauskas, V; Khivrich, V; Khomenkov, V; Kierstead, J; Klaiber-Lodewigs, J; Klingenberga, R; Kodys, P; Kohout, Z; Korjenevski, S; Koski, M; Kozlowski, R; Kozodaev, M; Kramberger, G; Krasel, O; Kuznetsov, A; Kwan, S; Lagomarsino, S; Lassila-Perini, K; Lastovetsky, V; Latino, G; Lazanu, S; Lazanu, I; Lebedev, A; Lebel, C; Leinonen, K; Leroy, C; Li, Z; Lindstrom, G; Linhart, V; Litovchenko, A; Litovchenko, P; Lo Giudice, A; Lozano, M; Luczynski, Z; Luukka, P; Macchiolo, A; Makarenko, LF; Mandic, I; Manfredotti, C; Manna, N; Marti i Garcia, S; Marunko, S; Mathieson, K; Melone, J; Menichelli, D; Messineo, A; Metcalfe, J; Miglio, S; Mikuz, M; Miyamoto, J; Monakhov, E; Moscatelli, F; Naoumov, D; Nossarzewska-Orlowska, E; Nysten, J; Olivera, P; OShea, V; Palvialnen, T; Paolini, C; Parkes, C; Passeri, D; Pein, U; Pellegrini, G; Perera, L; Petasecca, K; Piemonte, C; Pignatel, GU; Pinho, N; Pintilie, I; Pintilie, L; Polivtsev, L; Polozov, P; Popa, A; Popule, J; Pospisil, S; Pozza, A; Radicci, V; Rafi, JM; Rando, R; Roeder, R; Rohe, T; Ronchin, S; Rott, C; Roy, A; Ruzin, A; Sadrozinski, HFW; Sakalauskas, S; Scaringella, M; Schiavulli, L; Schnetzer, S; Schumm, B; Sciortino, S; Scorzoni, A; Segneri, G; Seidel, S; Seiden, A; Sellberg, G; Sellin, P; Sentenac, D; Shipsey, I; Sicho, P; Sloan, T; Solar, M; Son, S; Sopko, B; Sopko, V; Spencer, N; Stahl, J; Stolze, D; Stone, R; Storasta, J; Strokan, N; Sudzius, M; Surma, B; Suvorov, A; Svensson, BG; Tipton, P; Tomasek, M; Tsvetkov, A; Tuominen, E; Tuovinen, E; Tuuva, T; Tylchin, M; Uebersee, H; Uher, J; Ullan, M; Vaitkus, JV; Velthuis, J; Verbitskaya, E; Vrba, V; Wagner, G; Wilhelm, I; Worm, S; Wright, V; Wunstorf, R; Yiuri, Y; Zabierowski, P; Zaluzhny, A; Zavrtanik, M; Zen, M; Zhukov, V; Zorzi, N

Published: JUL 1 2005, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 546, 107, DOI: 10.1016/j.nima.2005.03.044

The envisaged upgrade of the Large Hadron Collider (LHC) at CERN towards the Super-LHC (SLHC) with a 10 times increased luminosity of 10(35) cm(-2) s(-1) Will present severe challenges for the tracking detectors of the SLHC experiments. Unprecedented high radiation levels and track densities and a reduced bunch crossing time in the order of 10 ns as well as the need for cost effective detectors have called for an intensive R&D program. The CERN RD50 collaboration "Development of Radiation Hard Semiconductor Devices for Very High Luminosity Colliders" is working on the development of semiconductor sensors matching the requirements of the SLHC. Sensors based on defect engineered silicon like Czochralski, epitaxial and oxygen enriched silicon have been developed. With 3D, Semi-3D and thin detectors new detector concepts have been evaluated and a study on the use of standard and oxygen enriched p-type silicon detectors revealed a promising approach for radiation tolerant cost effective devices. These and other most recent advancements of the RD50 collaboration are presented. (c) 2005 Elsevier B.V. All rights reserved.

4178. Influence of the grain size on polaron transport in nanostructured La2/3Ca1/3MnO3 evidenced by EPR

Authors: Raita, O; Grecu, MN; Filip, X; Toloman, D; Giurgiu, LM; Idziak, S; Hoffmann, SK

Published: JUL 2005, ACTA PHYSICA POLONICA A, 108, 118, DOI: 10.12693/APhysPolA.108.113

We report an electron paramagnetic resonance investigation of the grain size effects on the polaron transport in the paramagnetic regime of nanosized La2/3Ca1/3MnO3 manganites. The temperature dependences of the EPR integral intensity were analyzed in terms of spin-spin exchange interaction and small polaron hopping scenarios. The polaron activation energy decreases with the reduction of the grain size. A discussion is given concerning the factors which could explain the observed change.

4179. Thermal stability of atomic layer deposited Zr : Al mixed oxide thin films: An in situ transmission electron microscopy study

Authors: Nistor, LC; Richard, O; Zhao, C; Bender, H; Van Tendeloo, G

Published: JUL 2005, JOURNAL OF MATERIALS RESEARCH, 20, 1750, DOI: 10.1557/JMR.2005.0217

The thermal stability of amorphous Zr:Al mixed oxide films of different composition, produced on (001) silicon wafers by the atomic layer deposition method is studied, by transmission electron microscopy during in situ heating experiments. The temperatures at which phase separation and crystallization occur are composition dependent. The crystallization of thick films (55-70 nm), deposited on HF-treated silicon surfaces covered with a 15 cycles Al2O3 layer, results in the formation of cubic ZrO2 and cubic gamma-Al2O3. In very thin films (5 nm), deposited on silicon surfaces covered with a 0.5 nm SiO2 thin film, the formation of tetragonal zirconium disilicide (ZrSi2) is observed in the microscope vacuum, at temperatures above 900 degrees C. This effect depends on the thickness of the as deposited thin film.

4180. Spin magnetoconductance in the mesoscopic spin-interferometer

Authors: Aldea, A; Tolea, M; Zittartz, J

Published: JUL 2005, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 28, 202, DOI: 10.1016/j.physe.2005.03.013

We investigate the properties of the electron spin-transmission through an Aharonov-Bohm interferometer with an embedded two-dimensional (2D) multilevel quantum dot containing magnetic impurities. A suitable formalism is developed. The amplitude and the phase of the flip- and non-flip-transmittances are calculated numerically as function of the magnetic field. The effects induced by the exchange interaction and those arising from the 2D character of the dot are shown. (c) 2005 Elsevier B.V. All rights reserved.