National Institute Of Materials Physics - Romania

Publications

838 articles found

421. Tuning structural and magnetic properties of Fe films on Si substrates by hydrogenation processing

Authors: Sandu, SG; Palade, P; Schinteie, G; Birsan, A; Trupina, L; Kuncser, V

Published: FEB 2014, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 181, 32, DOI: 10.1016/j.mseb.2013.11.004

In order to study specific phenomena at ferromagnetic/semiconducting interfaces, of potentially high interest in spintronics and information technology, structural aspects and magnetic properties of Fe thin films grown on Si(001) substrates by RF sputtering have been investigated using Fe-57 conversion electron Mossbauer spectroscopy (CEMS) and magneto-optic Keer effect (MOKE). Films of different thicknesses have been deposited either directly on crystalline Si substrates or on Cu buffer layers. An inherent Fe oxide layer is observed in all as prepared films, with a relative thickness decreasing drastically with the deposition time. The Cu buffer layer does not diminish either the interfacial diffusion or the oxidation process. An efficient method to prepare sharper oxygen- and silicon-free interfaces for an improved spin injection, via thermal treatment in hydrogen atmosphere, is proposed. Accordingly, the hydrogenation treatments are very efficient in the modification of the ferromagnetic film structure, phase composition, magnetic properties and interfacial mixing. (C) 2013 Elsevier B.V. All rights reserved.

422. BiFeO3 doped-BNT-BT0.08 piezoelectric and magnetic nanowires, derived from sol-gel precursor

Authors: Cernea, M; Trupina, L; Vasile, B; Bartha, C; Radu, R; Chirila, C; Teodorescu, A

Published: JAN 10 2014, JOURNAL OF NANOPARTICLE RESEARCH, 16, DOI: 10.1007/s11051-013-2231-z

Lead-free piezoelectric (Bi0.5Na0.5)(0.92)Ba0.08TiO3, doped with 5 mol %BiFeO3 (BNT-BT-BFO) nanowires was prepared from its corresponding precursor sol. A polycarbonate membrane with the thickness of 30 mu m and the pore diameter of 100 nm was used as template. Nanowires with average diameter of similar to 80 nm and different lengths of a few microns were prepared from BNT-BT-BFO precursor sol with similar to 0.03 M concentration. Ferroelectric and piezoelectric characterizations of BNT-BT-BFO nanowires were performed using AFM-PFM equipment. The HR-TEM micrograph of nanocrystals, SAED patterns, and XRD pattern indicated that BNT-BT-BFO nanowires crystallized on the lattice of rhombohedral (Na0.5Bi0.5TiO3) phase. The BNT-BT-BFO nanowires showed a significant piezoelectric response, suggesting a good piezoelectric behavior. The saturation magnetization of the nanowires, measured at room temperature and at 5 kOe magnetic field, was Ms = 0.061 emu/g. A saturated ferromagnetic hysteresis loop has been also obtained.

423. Synthesis and Raman scattering of multiferroic Fe-Pb(Zr0.2Ti0.8)O-3 core-shell wire arrays

Authors: Baibarac, M; Sima, M; Matei, E; Pasuk, I; Mihut, L

Published: JAN 2014, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 211, 205, DOI: 10.1002/pssa.201330062

A new method to fabricate an Fe-PZT core-shell wire arrays developed in three steps is reported in this paper. This involves the electrochemical growth of an iron wire array by template method, deposition by spin coating of the PZT precursor prepared by sol-gel technique on the iron wires surface and annealing treatment to obtain Fe-PZT core-shell structures. The structure of the Fe-PZT core-shell wire array was characterized by scanning electron microscopy (SEM) and Raman scattering. Raman lines situated at 372 and 575cm(-1) indicate the formation of the FeO particles on the Fe wires surface as a result of the use of an aqueous solution for electrochemical synthesis. An upshift of Raman lines of Fe decorated with FeO wires was observed after formation of Fe-PZT core-shell structure. The annealing treatment of this structure involves a partial transformation of the FeO into Fe2O3 particles both with structure rhombohedral and cubic that were evidenced by Raman lines peaked at 243 and 497cm(-1), respectively. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

424. Compact antenna using ZST low-loss high dielectric constant material

Authors: Geambasu, DC; Leontin, T; Banciu, MG; Nedelcu, L; Nicolaescu, I

Published: 2014, 2014 22ND TELECOMMUNICATIONS FORUM TELFOR (TELFOR), 809, DOI:

Investigations on compact dielectric resonator antennas arc presented. Low-loss, high dielectric constant zirconium tin titanate (ZST) material was prepared by using solid state reaction method. The ZST resonators exhibit 36 dielectric relative permittivity, dielectric loss tangent 5x10(-4) and resonant frequency temperature coefficient between -4 to +4 ppm/degrees C. The developed resonators are very attractive for probe-fed resonator antenna for 2.66 GHz.

425. Selective adsorption of contaminants on Pb(Zr,Ti)O-3 surfaces shown by X-ray photoelectron spectroscopy

Authors: Stoflea, LE; Apostol, NG; Trupina, L; Teodorescu, CM

Published: 2014, JOURNAL OF MATERIALS CHEMISTRY A, 2, 14392, DOI: 10.1039/c4ta02660h

X-ray photoelectron spectroscopy (XPS) analyses of lead zirco-titanate Pb(Zr,Ti)O-3(001) single crystal thin layers as a function of the time spent between sample preparation by pulsed laser deposition and introduction in to a ultrahigh vacuum revealed the fact that freshly prepared samples showed a shift of the C 1s towards a higher binding energy, together with shifts of core levels originating from the substrate (particularly Ti 2p and O 1s) towards a lower binding energy. This behaviour is explained by considering that the molecules of contaminants (fatty acids, alcohols, esters) are adsorbed preferentially on areas exhibiting outwards polarization P(+). Thus, photoelectrons originating from contaminants will have larger binding energies because of the charge state of the P(+) areas, whereas the substrate XPS signals from these P(+) areas are attenuated by the contaminants, with the consequence of a prevalence of XPS substrate signals originating from the P(-) areas, shifted towards lower binding energies. Piezoresponse force microscopy confirmed the assumptions derived from XPS results and suggests the existence of an interplay between the adsorption of contaminants and the surface polarization state.

426. 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.

427. Formation and annealing of boron-oxygen defects in irradiated silicon and silicon-germanium n(+)-p structures

Authors: Makarenko, LF; Lastovskii, SB; Korshunov, FP; Moll, M; Pintilie, I; Abrosimov, NV

Published: 2014, INTERNATIONAL CONFERENCE ON DEFECTS IN SEMICONDUCTORS 2013, 1583, 126, DOI: 10.1063/1.4865618

New findings on the formation and annealing of interstitial boron-interstitial oxygen complex (BiOi) in p-type silicon are presented. Different types of n(+)-p structures irradiated with electrons and alpha-particles have been used for DLTS and MCTS studies. Electronic excitation essentially changes the formation rate of BiOi. It has been found that the increase of oxygen content slows the BiOi annealing rate down. The activation energy of the BiOi dissociation has been determined and it was found that germanium doping does not change the activation energy.

428. Structural Characterization of Impurified Zinc Oxide Thin Films

Authors: Trinca, LM; Galca, AC; Stancu, V; Chirila, C; Pintilie, L

Published: 2014, ELECTROCERAMICS XIV CONFERENCE, 1627, 128, DOI: 10.1063/1.4901669

Europium doped zinc oxide (Eu:ZnO) thin films have been obtained by pulsed laser deposition (PLD). 002 textured thin films were achieved on glass and silicon substrates, while hetero-epilayers and homo-epilayers have been attained on single crystal SrTiO3 and ZnO, respectively. X-ray Diffraction (XRD) was employed to characterize the Eu:ZnO thin films. Extended XRD studies confirmed the different thin film structural properties as function of chosen substrates.

429. High-Order Modes in High Permittivity Cylindrical Dielectric Resonator Antenna Excited by a Wide Microstrip Line

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

Published: 2014, 2014 10TH INTERNATIONAL CONFERENCE ON COMMUNICATIONS (COMM), DOI:

The aim of the paper is to identify the modes that can be excited by a wide microstrip line, in a cylindrical DRA situated symmetrically above it, to study the radiating performances of these modes and to present their radiating patterns. We managed to identify thirteen high-order modes; among these modes, four of them: HEM112, TMme(311), TEme(112), and TEme(121) have high transmission performances.

430. Luminescent liquid crystalline materials based on palladium(II) imine derivatives containing the 2-phenylpyridine core

Authors: Micutz, M; Ilis, M; Staicu, T; Dumitrascu, F; Pasuk, I; Molard, Y; Roisnel, T; Circu, V

Published: 2014, DALTON TRANSACTIONS, 43, 1161, DOI: 10.1039/c3dt52137k

In this work we report our studies concerning the synthesis and characterisation of a series of imine derivatives that incorporate the 2-phenylpyridine (2-ppy) core. These derivatives were used in the cyclo-metalating reactions of platinum(II) or palladium(II) in order to prepare several complexes with liquid crystalline properties. Depending on the starting materials used as well as the solvents employed, different metal complexes were obtained, some of them showing both liquid crystalline behaviour and luminescence properties at room temperature. It was found that, even if there are two competing coordination sites, the cyclometalation process takes place always at the 2-ppy core with (for Pt) or without (for Pd) the imine bond cleavage. We successfully showed that it is possible to prepare emissive room temperature liquid crystalline materials based on double cyclopalladated heteroleptic complexes by varying the volume fraction of the long flexible alkyl tails on the ancillary benzoylthiourea (BTU) ligands.