National Institute Of Materials Physics - Romania

Publications

5781 articles found

2161. INFLUENCE OF PREPARATION STEPS ON THE PROPERTIES OF ELECTROSPUN ZnO FIBERS

Authors: Busuioc, C; Evanghelidis, A; Florica, C; Enculescu, I

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1578, DOI:

ZnO nanofibers were obtained by calcination of electrospun Zn(Ac)(2)center dot 2H(2)O/PMMA composite fibers and characterized by X-ray diffraction, scanning electron microscopy and photoluminescence spectroscopy. The thermal treatment led to polymer burning and polycrystalline hexagonal ZnO phase formation. The average fiber diameters range between 450 and 600 nm before calcination and 200 - 300 nm after calcination. PL investigation revealed a strong dependence of ZnO fibers emission band on the calcination temperature. Furthermore, electrical contacts were fabricated by photolithography and electric characteristics were measured.

2162. Higher-Order Modes in High-Permittivity Cylindrical Dielectric Resonator Antenna Excited by an Off-Centered Rectangular Slot

Authors: Avadanei, OG; Banciu, MG; Nedelcu, L

Published: 2014, IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, 13, 1588, DOI: 10.1109/LAWP.2014.2344860

In this letter, we study the higher-order modes excited in a high-permittivity cylindrical dielectric resonator antenna (DRA), situated asymmetrically on top of a rectangular slot in the ground plane of a microstrip line. Besides the modes excited by a symmetric positioning of the DRA above the feeding slot, we identified five new modes: TEme(010), TEme(011), TEme(210), TEme(020), and TM212 respectively. The higher-order modes offer to the DRA antenna some interesting features: They have different radiation patterns for different operating modes; modes with close resonance frequency give wideband capabilities; and sometimes, when a mode has poor performance in one polarization, it is possible that another mode with close frequency can compensate it.

2163. Engineering Magnetic Properties of Nanostructures via Size Effects and Interphase Interactions

Authors: Kuncser, V; Palade, P; Kuncser, A; Greculeasa, S; Schinteie, G

Published: 2014, SIZE EFFECTS IN NANOSTRUCTURES: BASICS AND APPLICATIONS, 205, 237, DOI: 10.1007/978-3-662-44479-5_7

Finite size effects and interfacial interactions as well as their influence on the magnetic properties of nanosized systems are discussed by starting from very basic principles of magnetism. Some preparation and subsequent processing tools for a proper engineering of the properties of such magnetic nanosized systems are introduced together with specific characterization tools. A summary of the most important technological applications related to size effects and interfacial interactions, with exemplifications starting from bio-medical applications of magnetic fluids to magnetoresitive multilayers for sensor applications are also provided.

2164. Technology of vanadium and its oxides based nanocomposite structures

Authors: Prilepov, V; Gasin, P; Chirita, A; Midoni, V; Spoiala, D; Keirush, P

Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 231, DOI:

The peculiarities of vanadium and its oxides based nanocomposite structures fabrication are brought in this paper. The selected fabrication technological conditions allow creating a V2O5 based dielectric matrix in which conducting clusters are uniformly distributed. Some optical and electrical properties of such structures are presented. It was shown that the obtained layers possess high charge sensitivity.

2165. Electroluminescence of OLED based IrQ(ppy)(2)-5Cl organometallic compound: Theoretical considerations

Authors: Polosaw, S; Ciobotaru, IC

Published: JAN-FEB 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 92, DOI:

The electroluminescence and current density versus applied voltage were measured for the OLED cell structure which contain IrQ(ppy)(2)-5Cl as emitting layer. Two parameters, emission quantum yield and charge transport behaviors, which influences the electroluminescence, were modeled mainly concerning the non-radiative rate constants, delocalization of the HOMO and LUMO states, internal reorganization energies and bandgap of IrQ(ppy)(2)-5Cl. The non-radiative constant rates were determined using the three zero-field splitting substates responsible for the phosphorescence model and shows an increasing of these rates together with a strong interaction with the polystyrene matrix. Delocalization of the HOMO and LUMO states on the quinoline ligand, together with the small reorganization energies and bandgap lowering indicates good charge transport properties for the IrQ(ppy)(2)-5Cl compound.

2166. COVERING OBLIQUELY DEPOSITED SiOx WITH POLYVINYL CARBAZOLE CHANGES THE ORIENTATION PROPERTIES

Authors: Frunza, S; Zgura, I; Frunza, L; Rasoga, O; Gheorghe, P; Petris, A; Vlad, VI

Published: 2014, ROMANIAN JOURNAL OF PHYSICS, 59, 744, DOI:

Alignment layers of polyvinylcarbazole (PVK) were obtained by withdrawing from different solutions in toluene onto glass plates having SiOx layers obliquely evaporated in vacuum at 82 degrees. The alignment direction of nematic liquid crystal molecules with cyan-end group imposed by bare SiOx layers is changed when these layers are coated with PVK; the same happens with over layers of polyvinylimidazole or of polyvinylcinnamate. The effect is inhibited by doping PVK with fullerene C60 (0.1%), when the liquid crystal orientation specific for bare SiOx obliquely evaporated substrates is obtained. Other nematic (with methoxy-end group) does not show change of the orientation properties by covering the SiOx obliquely deposited layers with the mentioned polymer over layers.

2167. Photoluminescence quenching it disordered semiconductors from point of view of the barrier-cluster-heating model

Authors: Banik, I; Popescu, M

Published: NOV-DEC 2014, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 16, 1284, DOI:

The aim of this article is in the first place to familiarize the readers with barrier-cluster-heating model of the non-crystalline semiconductors, then briefly and digestedly present some results achieved by physical phenomena explanation in non-crystalline semiconductors within the frame of this model. The barrier-cluster-heating model of disordered semiconductor gives new view on photoluminescence in disordered semiconductors, too. This model enables to explain Stokes shift, Street's empirical law, fatigue effect, PLE-characteristic, electric field influence on photoluminescence, and some other physical phenomena in disordered semiconductors, including the photoinduced structural changes.

2168. Transition in conduction mechanism in GeSi nanostructures

Authors: Palade, C; Lepadatu, AM; Stavarache, I; Teodorescu, VS; Ciurea, ML

Published: 2014, 2014 INTERNATIONAL SEMICONDUCTOR CONFERENCE (CAS), 58, DOI:

GeSi-based nanostructures show unique properties which make them suitable for integrated circuit technology. The strong interest is to enhance their electronic properties in order to improve the device performance. In order to obtain fundamental knowledge on the electrical transport taking place in GeSi nanostructures we have investigated the effects of different microstructures on the electrical behavior of GeSi nanostructured films, by modifying the annealing conditions. We manufactured GeSi nanostructured films with equiatomic composition and different structures by co-sputtering followed by adequate annealing under different temperatures. For determining the electrical behavior we performed and modeled current-temperature I - T characteristics taking into account the films structures. We found that the electrical behavior changes with the film structure by evidencing a transition in conduction mechanism. In films that are almost crystallized, being formed of small GeSi nanocrystals separated by thin amorphous regions, the I - T dependence at low temperature is due to thermally activated tunneling of carriers between neighboring nanocrystals. In contrast, in the completely crystallized films with big GeSi nanocrystals and crystallized borders between them, the electrical behavior is a typical polycrystalline one. Our findings help to clarify the conduction mechanisms taking place in GeSi nanostructures and to provide a route to electronic devices with high performance based on these materials.

2169. CLADDING WAVEGUIDES REALIZED IN Nd:YAG LASER MEDIA BY DIRECT WRITING WITH A FEMTOSECOND-LASER BEAM

Authors: Pavel, N; Salamu, G; Voicu, F; Jipa, F; Zamfirescu, M

Published: APR-JUN 2014, PROCEEDINGS OF THE ROMANIAN ACADEMY SERIES A-MATHEMATICS PHYSICS TECHNICAL SCIENCES INFORMATION SCIENCE, 15, 158, DOI:

We report on realization of buried cladding waveguides in Nd:YAG single crystal and ceramic media by direct femtosecond (fs)-laser writing technique. A classical technique that moves the laser medium transversally to the fs-laser beam, as well as a new scheme in which the laser medium has a motion on a helical trajectory during the inscribing process was used. The waveguides laser emission performances at 1.06 and 1.3 mu m have been investigated under the pump at 807 nm with a fiber-coupled diode laser that was operated both in quasi-continuous wave (quasi-cw) and in cw regimes. Laser pulses with energy of 3.45 mJ at 1.06 mu m and of 1.05 mJ at 1.3 mu m (with overall optical-to-optical efficiency of 0.26 and 0.08, respectively) were obtained from a 50 mu m in diameter circular waveguide that was inscribed by the helical-moving techniques in a 5.0-mm long, 1.1-at.% Nd:YAG ceramic medium. Characteristics of the laser emission recorded in cw operation are discussed.

2170. Tuned Sensitivity Towards H2S and NH3 with Cu Doped Barium Strontium Titanate Materials

Authors: Simion, CE; Sackmann, A; Teodorescu, VS; Rusti, CF; Piticescu, RM; Stanoiu, A

Published: 2014, ELECTROCERAMICS XIV CONFERENCE, 1627, 97, DOI: 10.1063/1.4901664

The different amount of Cu-doped Barium Strontium Titanate (BST) thick film materials have been tested for their gas-sensing performances towards NH3 and H2S under dry and 50% relative humidity (RH) background conditions. The optimum NH3 sensitivity was attained with 0.1mol% Cu-doped BST whereas the selective detection of H2S was highlighted using 5mol% Cu-doped BST material. No cross-sensitivity effects to CO, NO2, CH4 and SO2 were observed for all tested materials operated at their optimum temperature (200 degrees C) under humid conditions (50% RH). The presence of humidity clearly enhances the gas sensitivity to NH3 and H2S detection.