National Institute Of Materials Physics - Romania

Publications

5714 articles found

3281. Vortex melting line and anisotropy of a Ba2Ca3Cu4O8(O1-yFy)(2) multilayered superconductor

Authors: Shivagan, DD; Shirage, PM; Crisan, A; Tanaka, Y; Iyo, A; Kodama, Y; Tokiwa, K; Watanabe, T; Terada, N; Hamada, N

Published: SEP 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/9/095002

We have measured the vortex melting lines of high-pressure-synthesized Ba2Ca3Cu4O8(O1-yFy)(2) (nominal composition, 2y = 1.3, 1.6 and 2.0) F(2y)-0234 multilayered high-T-c superconductor using fundamental and third harmonic susceptibility responses carried out on preferentially oriented crystallites with very low ac field amplitude (5 mu T) and in applied dc fields up to 6 T. The vortex melting lines of all three F-substituted samples show interesting doping dependence and are very well described by the commonly accepted theory of melting lines. Interestingly, we discovered that the models describing the temperature dependence of the in-plane London penetration depth also depend on the doping level: the 3D XY model for the nearly-optimum-doped sample [F(1.3)], the mean-field theory for the under-doped sample [F(1.6)] and the two-fluid model for the heavily-under-doped sample [F(2.0)]. We found that the vortex melting lines in F-0234 are determined by the interplay in the coupling of pancake vortices through the charge reservoir layer (CRL), and through the block of inner CuO2 planes (IPs), respectively. The anisotropy values (47 for the near-optimally-doped sample) derived from experimental vortex melting lines are consistent with the values obtained by first-principles electronic-band-structure calculations.

3282. Simulation of nanoparticle formation by condensation from the gaseous phase

Authors: Nicolae, I; Popescu, M

Published: SEP 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2473, DOI:

The paper reports the computer simulation of nanoparticle formation based on classical homogenous condensation theory with the purpose of understanding nanoparticle formation and the dependence of their size distribution on process parameters. The simulation has been performed for the case of silicon. The process of condensation with the formation of clusters due to the high cooling speed (similar to 10(4)-10(5) K/s) is considered.

3283. Hybrid metal (gold)-inorganic (silica) nanoparticles: Synthesis, characterization, and spin-labeling

Authors: Ionita, P; Ghica, C; Caproiu, MT; Ionita, G

Published: SEP 2008, JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS, 18, 419, DOI: 10.1007/s10904-008-9210-3

Water-soluble gold nanoparticles, capped with captopril, have been synthesized and characterized. Their average size is 2.3 nm, with a spherical shape. These gold nanoparticles can be easily labeled with stable free radicals (4-amino-tempo) by a coupling reaction performed in the presence of 2-ethoxy-1-ethoxycarbonyl-1,2-dihydroquinoline (EEDQ). Both synthesized and spin-labeled gold nanoparticles can be incorporated into much bigger (100 nm) silica nanoparticles using the Stober method, thus forming hybrid metal (gold)-inorganic (silica) nanoparticles. These hybrid silica nanoparticles (containing or not spin-labeled gold nanoparticles) can be easily spin-labeled with another stable free radical (4-isocyanato-tempo), leading to the formation of a double spin-labeled material. In this way, some stable free radicals are attached on the gold surface while others are attached on the silica surface. Three types of EPR spectra were recorded and discussed for the hybrid gold-silica nanoparticles: (1) where the spin labels are attached to the embedded gold nanoparticles, (2) where the spin labels are attached to the silica nanoparticles, and (3) in the case of the double spin labeled material where both gold and silica nanoparticles are spin-labeled. Influence of different solvents on the EPR spectra is also discussed.

3284. Iron oxide colloids and their heterogenization by silica sol-gel entrapment: Catalytic and magnetic properties

Authors: Neatu, F; Kraynov, A; D'Souza, L; Parvulescu, VI; Kranjc, K; Kocevar, M; Kuncser, V; Richards, R

Published: AUG 31 2008, APPLIED CATALYSIS A-GENERAL, 346, 35, DOI: 10.1016/j.apcata.2008.04.024

Fe3O4 colloids modified by the chiral ligand cinchonidine were prepared with the goal of obtaining a magnetic and catalytic nano-material and were subsequently embedded in silica to form a heterogeneous catalyst. The systems were characterized by TEM and XRD measurements, while the Mossbauer technique was applied for measuring the magnetic properties of the Fe3O4 colloids. The hyperfine magnetic field distribution was consistent with one type of Fe oxide, namely, the magnetite (Fe304). These colloids, both as 'quasi-homogenous catalysts' (or soluble heterogeneous catalysts) and embedded in silica (heterogeneous catalysts) were employed in the selective hydrogenolysis of complex bicyclo[2.2.2]oct-7-enes (bicyclo[2.2.2]oct-2-enes when unsubstituted). (C) 2008 Published by Elsevier B.V.

3285. 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.

3286. Phase diagram of a lattice of vortex molecules in multicomponent superconductors and multilayer cuprate superconductors

Authors: Tanaka, Y; Shivagan, DD; Crisan, A; Iyo, A; Shirage, PM; Tokiwa, K; Watanabe, T; Terada, N

Published: AUG 2008, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 21, DOI: 10.1088/0953-2048/21/8/085011

The Abrikosov lattice in the multilayer cuprate superconductor CuBa2Ca3Cu3Oy (Cu-1223) has been experimentally and theoretically demonstrated to be composed of vortex molecules. Cu-1223 is considered to be a typical multicomponent superconductor. We show that in such a system the rotational freedom around the axis of the vortex molecular tube generates orientational disorder and the orientational glass (or crystal) phase, which is never present in conventional vortex lattices consisting of axisymmetric vortices. The emergence of the orientational glass phase and orientational order phase with orthorhombic distortion is a general property of vortex molecule lattices of the multiband type of multicomponent superconductors.

3287. 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.

3288. Fe-catalyzed carbon nanotubes growth on fluidized powders by remote radiofrequency plasma beam

Authors: Vizireanu, S; Stoica, D; Birjega, R; Ghica, C; Teodorescu, V; Nistor, L; Ganea, R; Dinescu, G

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2060, DOI:

The paper reports the application of a new method combining the Plasma Assisted Chemical Vapour Deposition with the Fluidized Bed Reactor principles for the production of carbon nanotubes on powdered catalysts. An argon plasma beam injected with acetylene in presence of hydrogen was used as fluidized environment for targeting, smashing and mixing the catalytic powder located on the bottom of a cylindrical quartz reactor. The described technique generated plate-like or fibrous like carbon nanostructures on fine Fe particles and carbon nanotubes with 5-10 nm diameters on Fe supported ZSM-5 zeolite.

3289. The study of passive film formed on 316L stainless steed surface for orthopedic implant applications

Authors: Bebicu, I; Samide, A; Oprea, B; Tutunaru, B

Published: AUG 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 2158, DOI:

The characterization of passive films formed on 316L stainless steel surface implanted in a femur for 1 year is discussed according to Mossbauer Spectroscopy and scanning electron microscopy (SEM).The Mossbauer spectroscopy shown that surface layer consist mainly of oxidic species and suggested a possible apparition of a ferrite phase on surface In according to Mossbauer Spectroscopy, SEM shown that during implantation a change in the superficial microstructure took place and a corrosion process was presently.

3290. The CMS experiment at the CERN LHC

Authors: Chatrchyan, S; Hmayakyan, G; Khachatryan, V; (...) Lungu, GA; (...) Onengut, G (CMS Collaboration)

Published: AUG 2008, JOURNAL OF INSTRUMENTATION, 3, S08004, DOI: 10.1088/1748-0221/3/08/S08004

The Compact Muon Solenoid (CMS) detector is described. The detector operates at the Large Hadron Collider (LHC) at CERN. It was conceived to study proton-proton (and lead-lead) collisions at a centre-of-mass energy of 14 TeV (5.5 TeV nucleon-nucleon) and at luminosities up to 10(34)cm(-2)s(-1) (10(27)cm(-2)s(-1)). At the core of the CMS detector sits a high-magnetic-field and large-bore superconducting solenoid surrounding an all-silicon pixel and strip tracker, a lead-tungstate scintillating-crystals electromagnetic calorimeter, and a brass-scintillator sampling hadron calorimeter. The iron yoke of the flux-return is instrumented with four stations of muon detectors covering most of the 4 pi solid angle. Forward sampling calorimeters extend the pseudo-rapidity coverage to high values (vertical bar eta vertical bar <= 5) assuring very good hermeticity. The overall dimensions of the CMS detector are a length of 21.6 m, a diameter of 14.6 m and a total weight of 12500 t.