National Institute Of Materials Physics - Romania

Publications

5714 articles found

2951. Backward Couplers Using Coupled Composite Right/Left-Handed Transmission Lines

Authors: Mocanu, IA; Militaru, N; Lojewski, G; Petrescu, T; Banciu, MG

Published: 2010, PROCEEDINGS OF THE 2010 8TH INTERNATIONAL CONFERENCE ON COMMUNICATIONS (COMM), 270, DOI:

A new asymmetric backward coupler is obtained by edge-coupling two types of composite right/left handed (CRLH) lines. This novel coupler is analyzed in a microwave range (1-10 GHz) and the magnitude of the scattering parameters reveals tight coupling effects (even 0 dB) in a dual frequency band and also very good directivity in the working band.

2952. Self-assembled artificial pinning centres in thick YBCO superconducting films

Authors: Mikheenko, P; Abell, JS; Sarkar, A; Dang, VS; Kechik, MMA; Tanner, JL; Paturi, P; Huhtinen, H; Babu, NH; Cardwell, DA; Crisan, A

Published: 2010, 9TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS 09), 234, DOI: 10.1088/1742-6596/234/2/022022

Strong, artificial pinning centres are required in superconducting films of large thickness for power applications in high magnetic fields. One of the methods for the introduction of pinning centres in such films is substrate decoration, i.e., growing nanoscale islands of certain materials on the substrate prior to the deposition of the superconducting film. Two other methods are building up a layered distribution of a second phase and homogeneous incorporation of second phase inclusions from a compositional target. In this paper, we compare the effectiveness of these methods in terms of the type of the self-assembly of nanoparticles. The comparison is made over a large set of YBa2Cu3O7 films of thickness up to 6.6 mu m deposited with Au, Ag, Pd, LaNiO3, PrBa2Cu3O7, YBCO, BaZrO3 and Gd2Ba4CuWOy nanoparticles. It is found that substrate-decoration self-assembly is able to provide higher critical current in low magnetic field than the incorporation of homogeneous second phase in the sample microstructure. By specific modification of substrate decoration we achieved the self-field critical current per centimetre of width of 896 A/cm at 77.3 K and 1620 A/cm at 65 K in a film of thickness of 4.8 mu m.

2953. Mossbauer investigation of hyperfine interactions in dilute Fe-SnO2 nanoparticles

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

Published: 2010, INTERNATIONAL CONFERENCE ON THE APPLICATIONS OF THE MOSSBAUER EFFECT (ICAME 2009), 217, DOI: 10.1088/1742-6596/217/1/012110

We present a Mossbauer (MS) analysis on the nanoparticle system xSnO(2)-(1-x)alpha-Fe2O3, (x is an element of [0.995 divided by 0.925]). The samples were prepared by a hydrothermal route and have been 50 % enriched in Fe-57. The MS spectra were recorded at room (RI) and liquid nitrogen temperature (LNT). Below x = 0.975 the MS consist in a paramagnetic pattern, while at x 0.975 magnetic hyperfine interactions were evidenced. The observed coexistence of paramagnetic and ordered magnetic phases is discussed by taking into account the role of oxygen vacancies (square), Sn-O and Sn-square distances together with the iron-oxygen configurations.

2954. Switching mechanism in amorphous chalcogenides

Authors: Popescu, M; Simandan, ID

Published: 2010, 16 ISCMP: PROGRESS IN SOLID STATE AND MOLECULAR ELECTRONICS, IONICS AND PHOTONICS, 253, DOI: 10.1088/1742-6596/253/1/012014

The electrical switching in solid compositions based on chalcogenide materials is discussed. Different mechanisms proposed for switching effect are reviewed. A new description of the switching phenomenon is done. The switching is regarded as due to formation and breaking of the links between the dendrites of crystalline nuclei in bulk materials, as a consequence of the energy pumped by an electrical field. This mechanism explains the very short switching time (<20ns), the possibility to get smart memories based on multisteps of resistivity and the high number of cycles supported by the cell (10(16)).

2955. Magnetic Nanocomposites for Permanent Magnets

Authors: Tolea, F; Sofronie, M; Birsan, A; Schinteie, G; Kuncser, V; Valeanu, M

Published: 2010, TRENDS IN NANOPHYSICS: THEORY, EXPERIMENT AND TECHNOLOGY, 296, DOI: 10.1007/978-3-642-12070-1_12

The influence of different crystallization conditions on the microstructure and magnetic hardening of RE-Fe-B amorphous ribbons with different Fe concentrations and Pr and Nd as rare earth elements was analyzed. The microalloying effects of Zr and Ti substitution on the evolution of crystallization process and the magnetic hardening was also discussed. The final aim of this experimental study was to obtain performing exchange spring magnets with as much as lower content of the expensive RE material.

2956. Luminescence of dye-doped KAP and KDP nanorods

Authors: Enculescu, M; Trautmann, C

Published: MAR-JUL 2010, RADIATION MEASUREMENTS, 45, 604, DOI: 10.1016/j.radmeas.2009.11.015

Rods of potassium acid phthalate (KAP) and potassium dihydrogen phosphate (KDP) doped with rhodamine 6G (Rh 6G) were grown using the template approach. Pores of hundreds of nanometers in diameter were obtained in polycarbonate (PC) foils after heavy ions irradiation and subsequent chemical etching. Crystallization from solution was used for filling the pores and the nanostructures were characterized using scanning electron microscopy and photoluminescence spectroscopy studies. SEM images of micro- and nano-rods (300 nm and 2.5 mu m diameter) indicate a crystalline growth tendency. When exciting the PC foils containing rods of 100 nm diameter emission bands appear at 581 nm for Rh 6G doped KAP and at 602 nm for Rh 6G doped KDP. A shift of the emission bands towards red was observed when the luminescent properties of the rods with diameters of 100 nm were compared with the luminescent properties of the bulk crystals and of the micrometrical sized rods. (C) 2009 Elsevier Ltd. All rights reserved.

2957. Semiconductor Hybrid Structure: Nanowires Embedded in a Matrix from the Same Material

Authors: Sima, M; Vasile, E; Sima, M; Matei, E

Published: 2010, SEMICONDUCTORS, METAL OXIDES, AND COMPOSITES: METALLIZATION AND ELECTRODEPOSITION OF THIN FILMS AND NANOSTRUCTURES, 25, 161, DOI: 10.1149/1.3318514

Hybrid systems obtained by incorporation of a nanostructurated material into a matrix from the same thermoelectric (TE) material are predicted to show an increased TE efficiency compared to classical bulk materials. The authors have synthesized Bi1.95Te2.7Se0.35 submicron wires by electrodeposition into a polycarbonate membrane; after polymer membrane dissolution, the wire array supported on a metallic film was electrochemically embedded in a Bi2Te2.65Se0.35 film in order to prepare a hybrid structure. Wires and hybrid structure were analyzed by scanning electron microscopy (SEM), energy X-ray spectrometry (EDX) and X-ray diffraction (XRD).

2958. Eulityte glasses - synthesis and characterization

Authors: Berbecaru, C; Alexandru, HV; Polosan, S

Published: 2010, PHYSICA STATUS SOLIDI C: CURRENT TOPICS IN SOLID STATE PHYSICS, VOL 7, NO 9, 7, DOI: 10.1002/pssc.200983770

Oxides glasses are suitable for electronic and optoelectronic applications (band gap higher than 3 eV). Eulytite glasses were obtained from Bi4GeO14 sintered powder or mixture oxides powders Bi2O3-GeO2. The powders rapidly heated and melted at 1050 degrees C for 5 divided by 10 min was poured on the graphite plates under the glass transition temperature. Structural SEM, XRD and EDX investigations were performed at room temperatures. The frequency dependence of the permittivity and loss (45 Hz divided by 5 MHz) was investigated on a large temperature range between -140 and +375 degrees C. The permittivity and loss increase with the temperatures increase and decrease with the frequency increase. An activation energy of 0.88 kcal/mol, comparable to the thermal energy RT = 0.65 kcal/mol, was found for cluster formation on 150 divided by 200 degrees C temperature range. The jump of permittivity on the range 275 divided by 325 degrees C suggest an incipient glass transition at lower temperatures than 400 degrees C, as usually is accepted. The permittivity increase, correlated with the dipolar polarization was noticed at higher temperatures. The decrease of permittivity and loss in 10 divided by 100 kHz frequency range, at the mentioned temperatures, supports this assertion. The estimated relaxation times suggest the big clusters formation. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2959. X-ray excited luminescence and photoluminescence of Bi-4(GeO4)(3) glass-ceramics

Authors: Polosan, S; Secu, M

Published: MAR-JUL 2010, RADIATION MEASUREMENTS, 45, 411, DOI: 10.1016/j.radmeas.2010.01.040

Bi-4(GeO4)(3) glass materials have been characterized by X-ray excited luminescence, photoluminescence and cathodo-luminescence measurements. The materials were obtained by crystallization at different temperatures and their spectroscopic parameters were compared before and after crystallization. Thermoluminescence curves recorded after electron irradiation of BGO glass behave similarly to BGO crystals, showing several peaks between 408 K (135 degrees C) and 610 K (337 degrees C). The differences between the Bi-4(GeO4)(3) crystals and glass materials are believed to result from the random distribution of GeO4 tetrahedra around Bi3+ ions which influences the photoluminescence and TL parameters. The CL images of glass-ceramic samples obtained by partial crystallization at 600 degrees C show luminescent crystalline structures, which are probably responsible for the increase in scintillation efficiency. (C) 2010 Elsevier Ltd. All rights reserved.

2960. CARBON-CHALCOGENIDE NANOTUBE CONFIGURATION

Authors: Sava, F; Simandan, D

Published: JUL-SEP 2010, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 11, 235, DOI:

New nano-configuration has been modelled, based on nano-tubes of carbon and arsenic sulphide. The properties of this complex structure have been analysed. The modelling shows that the construction of composite nano-structures in different nano-systems are possible.