National Institute Of Materials Physics - Romania

Publications

5781 articles found

3021. 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)).

3022. 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.

3023. 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.

3024. 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).

3025. 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

3026. 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.

3027. 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.

3028. STUDY OF THE INTERACTIONS OF IONS IN SILICON: TRANSIENT PROCESSES AND DEFECT PRODUCTION

Authors: Lazanu, S; Lazanu, I; Iordache, G; Stavarache, I; Lepadatu, A; Slav, A

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 332, DOI:

The thermal spike model which takes into account both ionization and nuclear energy loss processes of the projectile as distinct electronic and atomic heat sources is used to describe transient processes induced by ions in silicon. The time and space dependencies of the lattice and electron temperatures near the projectile trajectory are calculated. The contribution of the rise in temperature on defect formation and annealing is considered.

3029. INFLUENCE OF THE DEPOSITION CONDITIONS ON THE PROPERTIES OF TiO2-Ge NANOCOMPOSITE FILMS SYNTHESIZED BY MAGNETRON CO-SPUTTERING

Authors: Slav, A; Stan, GE; Galca, AC

Published: 2010, 2010 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), VOLS 1 AND 2, 340, DOI:

A growing need for eco-friendly energy sources have led recently to a frantic search of new compositional systems for photovoltaic applications. The nanocomposite titania-germanium (TiO2-Ge) systems represent a new viable family of optoelectronic materials. Their structural, optical and electronic properties can be easily tailored by customizing the density and size of Ge dots in the TiO2 matrix. Early studies on TiO2-Ge nanocomposites have shown promises for their use as an alternative in photovoltaic applications. In this study we report the TiO2-Ge films synthesis by reactive magnetron co-sputtering. Their properties were evaluated by compositional (EDS), structural (XRD, FTIR) and optical (UV-Vis) characterizations.

3030. Direct Production of a Novel Iron-Based Nanocomposite from the Laser Pyrolysis of Fe(CO)(5)/MMA Mixtures: Structural and Sensing Properties

Authors: Alexandrescu, R; Morjan, I; Tomescu, A; Simion, CE; Scarisoreanu, M; Birjega, R; Fleaca, C; Gavrila, L; Soare, I; Dumitrache, F; Prodan, G

Published: 2010, JOURNAL OF NANOMATERIALS, 2010, DOI: 10.1155/2010/324532

Iron/iron oxide-based nanocomposites were prepared by IR laser sensitized pyrolysis of Fe(CO)(5) and methylmethacrylate (MMA) mixtures. The morphology of nanopowder analyzed by TEM indicated that mainly core-shell structures were obtained. X-ray diffraction techniques evidence the cores as formedmainly by iron/iron oxide crystalline phases. A partially degraded (carbonized) polymeric matrix is suggested for the coverage of the metallic particles. The nanocomposite structure at the variation of the laser density and of the MMA flow was studied. The new materials prepared as thick films were tested for their potential for acting as gas sensors. The temporal variation of the electrical resistance in presence of NO2, CO, and CO2, in dry and humid air was recorded. Preliminary results show that the samples obtained at higher laser power density exhibit rather high sensitivity towards NO2 detection and NO2 selectivity relatively to CO and CO2. An optimum working temperature of 200 degrees C was found.