National Institute Of Materials Physics - Romania

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5714 articles found

3151. A versatile gas-flow proportional counter for Mossbauer spectroscopy

Authors: Bibicu, I; Nicolescu, G; Cretu, C

Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_77

This article presents a versatile gas-flow proportional counter for surface and transmission Mossbauer spectroscopy, suitable for studies with Fe-57, Sn-119 and Eu-151 isotopes. The main advantages obtained by new design are: (1) the height of the detection volume can be changed in large limits from 0 to 38 mm, (2) the detection volume can be choose symmetrical or not in respect with anode plan, (3) the anode replacement is easily (4) and different anode configuration can be used. The characteristics of the detector, operating at room temperature, are reported.

3152. Synthesis and characterization of Mn2+ doped ZnS nanocrystals self-assembled in a tight mesoporous structure

Authors: Nistor, SV; Nistor, LC; Stefan, M; Mateescu, CD; Birjega, R; Solovieva, N; Nikl, M

Published: JUL-AUG 2009, SUPERLATTICES AND MICROSTRUCTURES, 46, 311, DOI: 10.1016/j.spmi.2008.10.001

We report the synthesis, by a surfactant-assisted liquid-liquid reaction, of nanocrystalline ZnS doped with 0.2 mol% Mn2+ ions self-assembled in a mesoporous structure. The XRD measurements demonstrate the formation of a sponge-like mesoporous material with a tight distribution of pores of 1.8 nm mean diameter built from cubic ZnS nanocrystals of 1.8 nm average size. TEM investigation confirms the formation of the mesoporous structure with walls of 3.1 nm mean thickness built from nanocrystallites of cubic ZnS. The ordering effect of self-assembling, which is reflected in the tight size distribution of crystallites and pores, might be also responsible for the well resolved EPR spectra, attributed to the presence of three types of isolated Mn2+ paramagnetic centers. (C) 2008 Elsevier Ltd. All rights reserved.

3153. Magnetism and Structural Phase Transformation in Fe/Fe oxide Nanopowders

Authors: Crisan, O; Crisan, AD; Skorvanek, I; Kovac, J

Published: 2009, 13TH INTERNATIONAL CONFERENCE ON RAPIDLY QUENCHED AND METASTABLE MATERIALS, 144, DOI: 10.1088/1742-6596/144/1/012027

Fe / Fe3O4 (magnetite) powders obtained by ball milling at room temperature, undergo an incomplete redox reaction with formation of FeO. This reaction is favoured due to the high energy developed during the milling and alloying. Concurrent effects of the milling, such as grain refinement down to the nanometric scale lead at the end of the milling processes to a mixed multiphased nanopowder, with a homogeneous dispersion of Fe and Fe oxide grains. Such ferromagnetic - antiferromagnetic systems are extensively studied due to their exchange bias properties, extremely useful in technological applications. We study the phase transformation that leads to a multiphased metal / oxide microstructure with an energy-dispersive in-situ X-ray diffraction experiment using the synchrotron radiation. This study allows direct collection of X-ray spectra after few minutes exposure, at selected temperatures, ranging between 20 degrees C and 1000 degrees C. Magnetic behavior has been studied for as-milled and annealed samples and the obtained magnetic parameters are correlated to the microstructure and phase composition at each stage of annealing. A significant exchange bias effect, related to FeO content, is observed for as-milled sample, the effect being less pronounced upon annealing the nanogranular powder.

3154. Spin configurations and interfacial diffusion in exchange bias and spin valve systems with Ir-Mn antiferromagnetic pinning layers

Authors: Kuncser, V; Schinteie, G; Palade, P; Mustata, I; Lungu, CP; Stefan, N; Chiriac, H; Vladoiu, R; Filoti, G

Published: 2009, ISIAME 2008, +, DOI: 10.1007/978-3-642-01369-0_62

Exchange bias and spin valve structures with Fe as ferromagnetic layers selectively enriched in Fe-57 and Ir-Mn of different compositions as antiferromagnetic pinning layers have been prepared by r.f. sputtering. Conversion Electron Mossbauer Spectroscopy and Magneto Optic Kerr Effect have shown that the local structure and interactions in the whole ferromagnetic layers, with direct influence on their magnetic reversal processes, depend on growing order of the layers and composition of the AF layer. Interfacial atomic diffusion is the main reason of perturbing the local structure of the ferromagnet. Mossbauer Spectroscopy is a powerfool tool which allows a detailed analysis of local configurations, in order to optimize the magnetic and giant magnetoresistive parameters of such multilayers of important technological applications.

3155. FIRST PRINCIPLES STUDY OF THE ELECTRONIC STRUCTURE OF Al/Ti:ZnO CRYSTAL

Authors: Plugaru, R; Plugaru, N

Published: 2009, CAS: 2009 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

We present results of ab initio calculations in the Local (Spin) Density Approximation, L(S)DA, of the electronic structure of Al and Ti doped ZnO crystal. Whereas both dopants modify the density of states at the Fermi energy, the structure and population of the impurity band is different in the two cases. Our results predict a non magnetic ground state for Al doped ZnO crystal, with the concentration x(Al) = 2-20 at. %. In the case of Ti doping the calculations predict a magnetic ground state and we obtain a magnetic moment localized on Ti ion of 1.14, 1.20, 1.28 and 1.54 mu(B)/Ti ion for x(Ti) = 2, 5, 10 and 20 %, respectively. We discuss the results in terms of the carriers role in the interplay between conductivity and magnetism in these materials.

3156. TRIBOLOGICAL APPLICATIONS OF THE ELECTRONICAL MICROSCOPY IN THE STUDY OF INDUSTRIAL LUBRICANTS

Authors: Radulescu, I; Radulescu, AV; Pogrion, NP

Published: 2009, BALTTRIB' 2009: V INTERNATIONAL CONFERENCE, PROCEEDINGS, +, DOI:

Study of industrial lubricants is made by the assistance of a transmission electronic n-kroscope (TEM) and electrons diffraction on a selected surface (SAED). Researches allow tribological characterization of the lubricant behavior, structural particles visualization and accomplish moi-pholo,-ical and dimensional evaluation of component particles of lubricants. Obtained data from H 46 - hydraulic oil, M30 multigrade motor oil, 5W30 winter motor oil, in fresh and used state and used toothing oil give information about forms, defects, dimensions, crystallographic phases and statistical parameters of industrial lubricants states.

3157. Ba(Zn1/3Ta2/3)O-3 Ceramics for Microwave and Millimeter-wave Applications

Authors: Alexandru, HV; Ioachim, A; Toacsan, MI; Nedelcu, L; Banciu, MG; Berbecaru, C; Voicu, G; Jinga, S; Andronescu, E

Published: 2009, INTERDISCIPLINARY TRANSPORT PHENOMENA: FLUID, THERMAL, BIOLOGICAL, MATERIALS, AND SPACE SCIENCES, 1161, 553, DOI: 10.1111/j.1749-6632.2008.04077.x

The Ba(Zn1/3Ta2/3)O-3 (BZT) ceramic samples were prepared by solid-state reaction and sintered in the range 1550-1650 degrees C for 2 h. Several methods-X-ray diffraction (XRD) and scanning electron microscopy (SEM)-were used for structural and morphological characterization. The unit cell distortion and the presence of the secondary phase content were studied by XRD. A long-range order with a 2:1 ratio of Ta and Zn cations on the octahedral positions of the perovskite structure was noticed with the increase of the sintering temperature. SEM investigations revealed polyhedral well-faceted grains and large grain size distribution. The dielectric properties in the microwave range were measured at room temperature and at 1 kHz on a large temperature interval (+/- 150 degrees C). The dielectric parameters were correlated with morphological and structural properties. Ceramic samples were annealed at 1410 degrees C for 30 h to improve the microwave properties. The dielectric constant of BZT samples measured at 6 GHz and at 1 kHz was between 27 and 28 on the whole temperature range, that is, typical values for BZT material. The temperature coefficient of the resonance frequency at 6 GHz exhibits positive values less than 6 ppm/degrees C.

3158. ADSORPTION COMPLEXES OF COLLAGENOUS POLYPEPTIDE-IONIC SURFACTANT IN AQUEOUS MEDIUM 1. THE FORMATION OF MICELLAR STRUCTURE OF IONIC SURFACTANT ADSORBED ONTO COLLAGENOUS POLYPEPTIDE CHAIN

Authors: Micutz, M; Staicu, T; Leca, M; Ghica, C

Published: NOV-DEC 2009, REVUE ROUMAINE DE CHIMIE, 54, +, DOI:

The paper reports on the main findings issued from studying the formation of adsorbed micelle-like clusters of ionic surfactant (sodium dodecyl sulfate and hexadecyl trimethylammonium bromide) onto molecule of collagenous polypeptide (collagen hydrolyzates and calfskin collagen type 1). Capillary viscometry, UV-circular dichroism, transmission electron microscopy and surfactant titration method were used to characterize the macromolecular component of the studied systems. To highlight the critical aggregation concentration (cac) and the critical saturation concentration (T-2) in the investigated polypeptide-surfactant systems, the steady-state fluorescence of pyrene (1(1)/1(3) rule) and the surface tension measurements (the droplet volume method) were availed. The study revealed a significant decrease of the effective micelle concentration of surfactant (cue) in the presence of polypeptide irrespective of pH and a critical concentration T-2 depending on the system composition and pH.

3159. Point and extended defects in irradiated silicon and consequences for detectors

Authors: Lazanu, S; Ciurea, ML; Lazanu, I

Published: 2009, PHYSICA STATUS SOLIDI C - CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 6, NO 8, 6, +, DOI: 10.1002/pssc.200881434

The interactions by which ions lose their energy in silicon are investigated at the microscopic level. this theoretical study put in evidence that the ionization could also represent a source of structural defects, and, contrary to the processes initiated by elementary particles, could generate extended primary defects, as, e.g. four-fold coordinated defects, due to the simultaneous breaking of bond for more neighbouring atoms in the lattice in a single interaction, in the ionisation core. The average energy transferred per atom is calculated, and also the energy spent by ionisation. The time dependence of the temperature in the ionisation core is derived in some simplifying assumptions. These contributions not considered yet in the studies of degradation of silicon detectors in radiation fields and could account for the discrepancies observed between models and measurements at microscopic versus device level for hadrons and ions. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

3160. EPR AND X-RAY DIFFRACTION INVESTIGATION OF SOME GREEK MARBLES AND LIMESTONES

Authors: Duliu, OG; Grecu, MN; Cristea, C

Published: 2009, ROMANIAN REPORTS IN PHYSICS, 61, 499, DOI:

12 different marble and limestone samples collected from well-known Greek quarries have been investigated by X-ray diffraction and electron paramagnetic resonance (EPR). Xray diffraction spectra permitted to determine both major (calcite and dolomite) and minor (quartz or magnesite) mineralogical components. EPR has been used to investigate the same samples unirradiated and after 10 kGy gamma-ray irradiation. The unirradiated samples display typical EPR spectra of Mn2+ in calcite and dolomite as well as a superposition of these while some samples displayed EPR free radicals signals of centers (low field signal) and centers (high field signal). From X-ray diffraction and EPR spectra it was possible to extract numerical values of several numerical parameters such as dolomite to calcite ratio, EPR intensity parameter, and low field to high field EPR signals intensity ratio. These values as well as the correlation coefficients between the digital functions that described the low field Mn2+ ions EPR line have been used as entry data for cluster analysis to quantify the resemblance and differences between analyzed samples.