National Institute Of Materials Physics - Romania

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5781 articles found

2141. 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.

2142. Gold nano-island arrays on silicon as SERS active substrate for organic molecule detection

Authors: Ignat, T; Husanu, MA; Munoz, R; Kusko, M; Danila, M; Teodorescu, CM

Published: JAN 1 2014, THIN SOLID FILMS, 550, 360, DOI: 10.1016/j.tsf.2013.10.151

Gold islands forming highly controlled arrays have been fabricated by two potential step electrochemical deposition method using nanopatterned Si surface templates. In the present work, the Raman scattering studies realized using 11-mercaptoundecanoic probe molecule showed that such structures exhibit an enhanced Raman signal compared with nanostructured physical deposited thin gold film on flat silicon substrate and can be valued as surface-enhanced Raman scattering substrates. Besides the more appropriate management of nano-island arrays distribution, the high ratio of their Raman signals can be explain by the epitaxial-like growth mechanism of themetallic nano-islands, clearly showed by X-ray diffraction studies. Furthermore, the substrates enabled reproducibility and stability detection due to the chemically assembling of organothiol molecules, the X-ray photoelectron spectroscopy studies confirming formation of the thiolate species which corresponds to Au - S bonds, and also, the unwanted 'hot-spots' are missing, which make them suitable for high sensitivity biosensing applications. (C) 2013 Published by Elsevier B.V.

2143. 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

2144. Room Temperature Ferromagnetic Mn:Ge(001)

Authors: Lungu, GA; Stoflea, LE; Tanase, LC; Bucur, IC; Radutoiu, N; Vasiliu, F; Mercioniu, I; Kuncser, V; Teodorescu, CM

Published: JAN 2014, MATERIALS, 7, DOI: 10.3390/ma7010106

We report the synthesis of a room temperature ferromagnetic Mn-Ge system obtained by simple deposition of manganese on Ge(001), heated at relatively high temperature (starting with 250 degrees C). The samples were characterized by low energy electron diffraction (LEED), scanning tunneling microscopy (STM), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), superconducting quantum interference device (SQUID), and magneto-optical Kerr effect (MOKE). Samples deposited at relatively elevated temperature (350 degrees C) exhibited the formation of similar to 5-8 nm diameter Mn5Ge3 and Mn11Ge8 agglomerates by HRTEM, while XPS identified at least two Mn-containing phases: the agglomerates, together with a Ge-rich MnGe similar to 2.5 phase, or manganese diluted into the Ge(001) crystal. LEED revealed the persistence of long range order after a relatively high amount of Mn (100 nm) deposited on the single crystal substrate. STM probed the existence of dimer rows on the surface, slightly elongated as compared with Ge-Ge dimers on Ge(001). The films exhibited a clear ferromagnetism at room temperature, opening the possibility of forming a magnetic phase behind a nearly ideally terminated Ge surface, which could find applications in integration of magnetic functionalities on semiconductor bases. SQUID probed the co-existence of a superparamagnetic phase, with one phase which may be attributed to a diluted magnetic semiconductor. The hypothesis that the room temperature ferromagnetic phase might be the one with manganese diluted into the Ge crystal is formulated and discussed.

2145. Elastic macro strain and stress determination by powder diffraction: spherical harmonics analysis starting from the Voigt model

Authors: Popa, NC; Balzar, D; Vogel, SC

Published: JAN 2014, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 47, 159, DOI: 10.1107/S1600576713029208

A new approach for the determination of the elastic macro strain and stress in textured polycrystals by diffraction is presented. It consists of expanding the strain tensor weighted by texture in a series of generalized spherical harmonics where the ground state is defined by the strain/stress state in an isotropic sample in the Voigt model. In contrast to similar expansions already reported by other authors, this new approach provides expressions valid for any sample and crystal symmetries and can easily be implemented in whole powder pattern fitting, including Rietveld refinement. An earlier article [Popa & Balzar (2001). J. Appl. Cryst. 34, 187-195] reported a similar model, but with a spherical harmonics expansion around the hydrostatic strain/stress state of the isotropic polycrystal. The availability of several different models is beneficial in order to allow one to select the representation in which the ground state is the closest to the actual stress state in the sample.

2146. Cylindrical semiconductor nanowires with constrictions

Authors: Racec, PN

Published: JAN 2014, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 251, 200, DOI: 10.1002/pssb.201349248

The energy dependence of the tunneling coefficient for a cylindrical semiconductor nanowire, i.e., a one-dimensional electron gas, with two constrictions is studied. Using the R-matrix formalism the localization probabilities at the resonant energies can be computed. They give decisive information about the physical meaning of the resonant peaks and dips that appear. The nanowire with two constrictions yields a well-defined system for the experimental evidence of the quasi-bound states of the evanescent channels. Clearly marked dips due to them should appear in the linear conductance at low temperatures. [GRAPHICS] Tunneling coefficient T(m) for a cylindrical nanowire with one or two constrictions, for a specific magnetic quantum number m. The influences of the geometrical parameters on the resonant energies are also shown. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

2147. The Effect of Surface Inhomogeneities on the Propagation of Elastic Waves

Authors: Apostol, BF

Published: JAN 2014, JOURNAL OF ELASTICITY, 114, 99, DOI: 10.1007/s10659-013-9428-3

We investigate the effect of the surface inhomogeneities (defects) on the propagation of the elastic waves in a semi-infinite isotropic solid body (half-space). A perturbation-theoretical scheme is devised for small surface defects (in comparison with the relevant elastic disturbances propagating in the body), and the elastic waves equations are solved in the first-order approximation. It is shown that surface defects generate both scattered waves localized (and propagating only) on the surface (two-dimensional waves) and scattered waves reflected back in the body. Directional effects, wave slowness and attenuation by diffusive scattering, or possible resonance effects are discussed.

2148. Dual emitter IrQ(ppy)(2) for OLED applications: Synthesis and spectroscopic analysis

Authors: Ciobotaru, IC; Polosan, S; Ciobotaru, CC

Published: JAN 2014, JOURNAL OF LUMINESCENCE, 145, 262, DOI: 10.1016/j.jlumin.2013.07.067

The synthesis of organometallic compound with iridium and two types of ligands, quinoline and phenylpyridine, was done successfully. The absorption spectra of this compound have shown broad peaks in a visible region assigned to metal-to-ligands charge transfer and in UV region assigned to intraligand absorptions. The photoluminescence spectra exhibit dual character in which the red emission is more intense than the green one. In cathodoluminescence measurements, under electron beam, the powder obtained after recrystallization from dichloromethane, shows similar behaviors with photoluminescence spectra. The cathodoluminescence images have shown a luminescent crystalline powder with triclinic structure. This compound exhibits combined vibrational modes, which proves the presence in the same molecule of both ligands. Density Functional Theory calculation was involved in order to identify the main vibrations of this compound. (C) 2013 Elsevier B.V. All rights reserved.

2149. 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.

2150. OPTICAL CHARACTERISTICS OF SULPHUR-PASSIVATED n-GaAs (100) SURFACE

Authors: Ghita, RV; Grigorescu, CEA; Secu, M; Predoi, D; Frumosu, F; Cotirlan, C; Feraru, ID

Published: OCT-DEC 2014, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 9, 1478, DOI:

A genuine GaAs surface is covered with a relatively thick layer (similar to 10 nm) of native oxide pinning the surface Fermi level within the band gap of semiconductor. The method presented in this work is related to the sulphur passivation by treating n-GaAs(100) and (110) in sulphide solutions (e.g pure ammonium sulphide and sulphur monochloride) that combines both chemical electronic passivation by reducing the surface state density. The effects of passivation were put into evidence by Photoluminescence measurements where it was observed the variation of state density. The presence of sulphur dipoles at surface was presented in a diagram of Second Harmonic Generation analysis and the general aspect of sulphur compound was identified by SEM images. The presence of the covalent bond Ga-S and the variation of surface barrier as well as the effect of crystal orientation were put into evidence by micro-Raman Spectroscopy. At the surface of n-GaAs it is developed an adherent layer of sulphur compound as a resul of chemical interaction of sulphur ions with n-GaAs surface.