National Institute Of Materials Physics - Romania

Publications

860 articles found

781. Manganese and copper doped CdS nanowire arrays preparation

Authors: Sima, M; Enculescu, I; Ioncea, A; Visan, T; Trautmann, C

Published: DEC 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 1198, DOI:

Manganese and copper doped CdS nanowires were obtained by the template technique in a two step process. In the first step metallic alloy CdMnCu nano and microwires were electrodeposited in ion track membranes with pore diameters in the range 150 nm-2 mum. In the following step the resulted nanowires were anodized in a sodium sulphide alkaline solution. Electron microscopy results show participation of the whole metallic wire in the anodization process; manganese and copper doped CdS wires are obtained The composition of micro and nanowires was determined by energy dispersive X-ray analysis.

782. The electrodeposition of semiconductor nanowires with thermoelectric properties using "template" method

Authors: Sima, M; Enculescu, I; Visan, T

Published: OCT 2004, REVISTA DE CHIMIE, 55, 746, DOI:

A binary telluride (CdTe) as well as a ternary telluride (PbSeTe) were electrodeposited in the pores of a track-etched polycarbonate membrane, resulting nanowires and nanotubes. Either acid or alkaline solutions were used for preparing CdTe compound, whereas the ternary PbSe1-xTex compound was deposited from an acid solution, only. The investigation of electrode mechanisms was performed by cyclic voltammetry. The nanostructures were visualized using scanning electron microscopy (SEM).

783. Copper tubes prepared by electroless deposition in ion track templates

Authors: Bercu, B; Enculescu, I; Spohr, R

Published: OCT 2004, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 225, 502, DOI: 10.1016/j.nimb.2004.06.011

Polycarbonate porous membranes were prepared by etching the ion tracks contained in foils irradiated in the fluence range of 1 ion/sample to 10(8) ions/cm(2). The membranes were used as templates for the preparation of tubes employing auto-catalytic copper deposition. A three-step process was used: pre-activation, activation and copper deposition. The deposition bath employed formaldehyde as reducing agent and tartrate as complexing agent. Copper nucleation was studied in order to optimize the activation steps thus allowing the preparation of thin tubes. The external diameters of the tubes ranged from 300 to 2000 nm. The inner diameters varied as a function of the time-of-exposure to the electroless bath. The length of the tubes was 30 mum, corresponding to the thickness of the foils. (C) 2004 Elsevier B.V. All rights reserved.

784. FexCu1-x alloys for permanent magnets

Authors: Kappel, W; Codescu, MM; Pasuk, I; Patroi, E; Kuncser, V; Valeanu, M; Predoi, D; Filoti, G

Published: SEP 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 978, DOI:

New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x=0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mossbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.

785. Tunneling properties of quantum dot arrays in a strong magnetic field

Authors: Moldoveanu, V; Aldea, A; Tanatar, B

Published: AUG 2004, PHYSICAL REVIEW B, 70, DOI: 10.1103/PhysRevB.70.085303

We study the transport properties of coherently coupled quantum dots in the quantum Hall regime within the Landauer-Buttiker formalism which captures and explains the experimentally observed features in terms of the spectral properties of the coupled dot system. The subpeak structure of the transmittance spectrum and the charging stability diagrams are obtained and discussed. The role of the intradot and interdot Coulomb interaction are pointed out. We show the subpeak evolution with the magnetic field and predict a specific oscillatory behavior of the Hall resistance in strong magnetic field which can be experimentally tested.

786. Disorder effects on the properties of two-dimensional finite systems in perpendicular magnetic field: the tight binding approach

Authors: Aldea, A; Nita, M; Dinu, V; Tolea, M

Published: JUL 2004, PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS, 241, 2096, DOI: 10.1002/pssb.200404781

We review some aspects concerning the disorder effects on the spectral properties of 2D electronic systems with relevance for the transport and orbital magnetism in perpendicular magnetic field. The lattice model and random Anderson disorder are used. The discussion is carried out separately for periodic and hard wall boundary conditions. The degree of localization is evidenced by the calculation of the inverse participation number of the eigenstates of the Hamiltonian and a striking asymmetry of the localization effect of states in the Landau band is reported. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

787. Magnetic interactions and spin structure in composite Fe/Nd2Fe14B systems

Authors: Kuncser, V; Valeanu, M; Lifei, F; Predoi, D; Palade, P; Schinteie, G; Crisan, O; Filoti, G

Published: MAY 2004, JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 272, 799, DOI: 10.1016/j.jmmm.2003.12.1279

Local magnetic interactions and spin configurations in alpha-Fe/Nd2Fe14B composite exchange-spring magnets have been investigated by Mossbauer spectroscopy and the magnetic behaviour was analysed by magnetometry. A new method for the evaluation of the coupling strength between soft and hard magnetic phases is proposed. (C) 2003 Elsevier B.V. All rights reserved.

788. On the optical properties of micro- and nanometric size PbI2 particles

Authors: Baibarac, M; Preda, N; Mihut, L; Baltog, I; Lefrant, S; Mevellec, JY

Published: APR 7 2004, JOURNAL OF PHYSICS-CONDENSED MATTER, 16, 2356, DOI: 10.1088/0953-8984/16/13/014

Scanning electron microscopy, Raman scattering, UV-VIS absorption spectroscopy and low temperature photoluminescence (PL) were used to examine small particles produced by the chemical reaction between Pb(NO3)(2) and KI in different liquid media: water, methanol, ethanol and acetonitrile. By stoichiometric changes in the synthesis reaction, platelets of PbI2 and rods probably of KPbI3 are produced. Regardless of shape and size, these particles exhibit almost the same PL, which consists of two intense bands centred around the 2.5 (E band) and 2.0 eV (G band), in turn similar to that of a crystalline slide or a micrometric powder, both prepared from a PbI2 single-crystal grown from the melt. Crystalline PbI2 platelets exhibit an E band with two components, at 2.49 (E-F band) and 2.47 eV (E-T band), originating in the recombination of the free and trapped excitons produced by inter-band irradiation. A close relation between the enhancement of the E-T and G band reveals that they are linked to the surface defects. For the rod-like particles, the PL spectrum is somewhat similar to that of a Pb2+ ion introduced into an alkaline halide lattice, which as for any ns(2) ion displays two emission bands, A(T) and A(X), whose correspondents are E and G bands.

789. Electrodeposition of CdTe nanorods in ion track membranes

Authors: Sima, M; Enculescu, I; Trautmann, C; Neumann, R

Published: MAR 2004, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 6, 125, DOI:

CdTe nanowires were electrodeposited in ion track membranes with pore diameters in the range 100-2000 nm. Acidic and basic baths were tested for obtaining materials with good stoichiometry. The cyclic voltammograms were compared for the case of deposition on a carbon rotating disc and on the porous membrane substrates, the differences being attributed to the additional resistance induced by the pores. For larger pores a tendency of growing hollow structures was observed.

790. Spin magnetization of a strongly correlated electron gas confined in a two-dimensional finite lattice

Authors: Nita, M; Dinu, V; Aldea, A; Tanatar, B

Published: FEB 2004, PHYSICAL REVIEW B, 69, DOI: 10.1103/PhysRevB.69.073106

The influence of disorder and interaction effects on the ground state polarization of the two-dimensional correlated electron gas is studied by numerical investigations of the unrestricted Hartree-Fock approach. With the model of Anderson disorder a continuous increase of the spin magnetization until the fully polarized regime is obtained. The ferromagnetic ground state is found to be favorable when the electron number is lowered and the interaction and disorder parameters are suitably chosen.