National Institute Of Materials Physics - Romania

Publications

5781 articles found

3721. Structural and sensing properties of a novel Fe/Fe2O3/polyoxocarbosilane core shell nanocomposite powder prepared by laser pyrolysis

Authors: Tomescu, A; Alexandrescu, R; Morjan, I; Dumitrache, F; Gavrila-Florescu, L; Birjega, R; Soare, I; Prodan, G; Bastl, Z; Galikova, A; Pola, J

Published: MAR 2007, JOURNAL OF MATERIALS SCIENCE, 42, 1846, DOI: 10.1007/s10853-006-0956-0

This paper reports about the synthesis and characterization of a novel Fe/Fe2O3/polyoxocarbosilane core shell nanocomposite as a material for gas-sensing applications. The nanocomposites (Fe-based nano cores enveloped with polymeric polyoxocarbosilane shells) were prepared by the IR laser co-pyrolysis of iron pentacarbonyl and hexamethyldisiloxane. The iron-based cores become superficially oxidized in atmosphere. The morphologies, chemical content and thermal behavior were studied by different analytical techniques. The sensing properties of the polymer-poor nanocomposite thick films were tested by measuring the variation of the electrical resistance in presence of CO and CH4, at a working temperature of 450 degrees C. Preliminary results indicate that for CO toxic gas, an n-p transitional character of the semiconducting iron oxide appears in humid relatively to dry air.

3722. Evidence for microwave-induced recrystallization in NiZn ferrites

Authors: Sorescu, M; Diamandescu, L; Ramesh, PD; Roy, R; Daly, A; Bruno, Z

Published: FEB 15 2007, MATERIALS CHEMISTRY AND PHYSICS, 101, 414, DOI: 10.1016/j.matchemphys.2006.07.006

A series of ferrites was prepared using the microwave method, starting with hematite as precursor in the Ni1-xZnxFe2O4 (x =0-1) system. After synthesis, the NiZn ferrite samples were irradiated with a microwave field for 90 s. X-ray diffraction (XRD) measurements were performed to yield the lattice constant as function of the amount x of Zn substitution, before and after irradiation. The lattice parameter was found to increase much slower with increasing x for the microwave irradiated specimens. Mossbauer spectroscopy was performed at room temperature and spectra were analyzed using the binomial distribution. For x = 0.4, 0.5 and 0.6 the resonance lines are much sharper for the irradiated samples and indicate that a microwave-induced recrystallization of the NiZn ferrites occurs in the composition range specified. (c) 2006 Elsevier B.V. All rights reserved.

3723. New polymeric structures designed for the removal of Cu(II) ions from aqueous solutions

Authors: Mocioi, M; Albu, AM; Mateescu, C; Voicu, G; Rusen, E; Marculescu, B; Mutihac, L

Published: FEB 5 2007, JOURNAL OF APPLIED POLYMER SCIENCE, 103, 1405, DOI: 10.1002/app.24655

New polymeric structures obtained by chemical transformations of maleic anhydride/dicyclopentadiene copolymer with triethylenetetraamine, p-aminobenzoic acid, and p-aminophenylacetic acid were used for the removal Cu(II) ions from aqueous solutions. The experimental values prove the importance of the chelator nature and of the macromolecular chain geometry for the retention efficiency. The retention efficiency (eta(r)), the retention capacity (Q(e)), and the distribution coefficient of the metal ion into the polymer matrix (K-d) are realized by evaluation of residual Cu(II) ions in the effluent waters, by atomic adsorption. Also are discussed the influence of pH, the thermal stability of the polymer, and their polymer-metal complex, as well as the particular aspects regarding the contact procedure and the batch time. Based on the polymers and polymer-metal complexes characterization a potential retention mechanism is proposed. All polymer supports as well theirs metal-complexes are characterized by ATD and FTIR measurements. (c) 2006 Wiley Periodicals, Inc.

3724. Admittance of planar two-terminal quantum systems

Authors: Wulf, U; Racec, PN; Racec, ER

Published: FEB 2007, PHYSICAL REVIEW B, 75, DOI: 10.1103/PhysRevB.75.075320

We develop an approach to calculate the admittance of effectively one-dimensional open quantum systems in random-phase approximation (RPA). The stationary, unperturbed system is described within the Landauer-Buttiker formalism taking into account the Coulomb interaction in the Hartree approximation. The dynamic changes in the effective potential are calculated microscopically from the charge-charge correlation function resulting from the stationary scattering states. We provide explicit RPA expressions for the quantum admittance. As a first example the case of a quantum capacitor is considered where we can derive a small-frequency expansion for the admittance which lends itself to an experimental testing of the theory. A comparison of the low-frequency expansion with the complete RPA expression shows that for a quantum capacitor a simple classical equivalent circuit with frequency-independent elements does not describe satisfactorily the quantum admittance with increasing frequency.

3725. Resolution functions of time-of-flight small-angle neutron scattering instruments with rectangular apertures

Authors: Grabcev, B

Published: FEB 2007, JOURNAL OF APPLIED CRYSTALLOGRAPHY, 40, 50, DOI: 10.1107/S0021889806047868

Analytic forms are found for resolution functions of small-angle neutron scattering instruments. The expressions are developed as a function of momentum transfer (Q) rather than separately in terms of neutron wavelength (lambda) and scattering angle (theta). Effects caused by the gravitational field as well as by quasi-elastic scattering are included. Explicit analytic forms for the transmission functions are proposed for both the incident and scattered beams, enabling careful analysis of any problem regarding small-angle scattering experiments. Due to the reciprocal mathematical relationship between lambda, theta and Q, [lambda, theta] space is employed to approach different aspects of the topic. Applications to time-of-flight instruments with rectangular apertures, including the choice of the most convenient instrumental parameters, the analysis of smearing effects and the data reduction to Q space, are presented.

3726. Ceria-based oxides as supports for LaCoO3 perovskite; catalysts for total oxidation of VOC

Authors: Alifanti, M; Florea, M; Parvulescu, VI

Published: JAN 31 2007, , DOI: 10.1016/j.apcatb.2005.10.037

3727. TEM characterization of extended defects induced in Si wafers by H-plasma treatment

Authors: Ghica, C; Nistor, LC; Bender, H; Richard, O; Van Tendeloo, G; Ulyashin, A

Published: JAN 21 2007, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 40, 400, DOI: 10.1088/0022-3727/40/2/016

Silicon hydrogenation is nowadays studied with the aim of developing and improving a technological method known as 'smart cut' used in the fabrication of 'silicon-on-insulator' devices. The goal of our study is to characterize the defects induced in silicon wafers after exposure to hydrogen RF plasma. Si < 001 > wafers have been treated at 250 degrees C under hydrogen RF plasma at 110 MHz, for various durations. The main features observed by transmission electron microscopy (TEM) are surface roughening and the presence of three kinds of defects: {111} planar defects, {100} planar defects and H bubbles. In this work a study using conventional TEM and high resolution transmission electron microscopy (HRTEM) techniques is presented on H bubbles and {100} planar defects induced in Si wafers by H-plasma treatment. The strain field around the defects is qualitatively characterized by diffraction contrast analysis and quantitatively by the geometrical phase method, by processing the HRTEM images.

3728. Localized energy levels generated in Magnetic Czochralski silicon by proton irradiation and their influence on the sign of space charge density

Authors: Scaringella, M; Menichelli, D; Bruzzi, M; Macchiolo, A; Piemonte, C; Zorzi, N; Candelori, A; Eremin, V; Verbitskaya, E; Pintilie, I

Published: JAN 11 2007, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION A-ACCELERATORS SPECTROMETERS DETECTORS AND ASSOCIATED EQUIPMENT, 570, 329, DOI: 10.1016/j.nima.2006.09.033

The microscopic damage produced in diodes made of n-type Magnetic Czochralski (MCz) silicon by 24 GeV and 26 MeV protons, up to the fluence of 1.3 x 10(15) cm(-2) 1 MeV equivalent neutrons, has been investigated and results are compared to the damage produced in devices made of standard Floating Zone (STFZ) silicon. It is found by means of Thermally Stimulated Currents (TSC) that the production of a radiation induced charged defect is enhanced in MCz, and might be in part responsible for the differences observed in the two materials at room temperature. The influence of defects on the sign of the space charge density has been studied by current transients at constant temperature i(T, t) and by Transient Current Technique (TCT). Type inversion is not revealed up to the highest investigated fluence. Full depletion voltage V-dep measurements versus fluence exhibits a minimum close to 2 x 10(14) cm(-2) 1 MeV equivalent neutrons; at the same fluence, V-dep measured as a function of annealing time changes its initial slope from positive to negative. It is shown by numerical simulations that these features can be accounted by the formation of a double junction, even in absence of type inversion. (c) 2006 Elsevier B.V. All rights reserved.

3729. Magnetic interactions in water based ferrofluids studied by Mossbauer spectroscopy

Authors: Kuncser, V; Schinteie, G; Sahoo, B; Keune, W; Bica, D; Vekas, L; Filoti, G

Published: JAN 10 2007, JOURNAL OF PHYSICS-CONDENSED MATTER, 19, DOI: 10.1088/0953-8984/19/1/016205

Various samples of ferrofluids consisting of colloidal suspensions of surfacted cobalt ferrite or magnetite nanoparticles in water were studied by x-ray diffraction and temperature dependent Mossbauer spectroscopy. Information about the particle mean size, the size dispersion and the effective magnetic anisotropy energy was obtained for each sample. The results are consistent with the formation of a magnetic dead layer at the particle surface, whose thickness depends on the surfactant - ferrite combination. The magnetic relaxation processes are faster in the colloidal suspensions of magnetite particles as compared with the suspensions of cobalt ferrite particles. The type of the surfactant also influences the magnetic relaxation behaviour, and hence the macroscopic properties of the ferrofluid at ambient temperature.

3730. Interpretation of abnormal AC loss peak based on vortex-molecule model for a multicomponent cuprate superconductor

Authors: Tanaka, Y; Crisan, A; Shivagan, DD; Iyo, A; Tokiwa, K; Watanabe, T

Published: JAN 2007, JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 46, 145, DOI: 10.1143/JJAP.46.134

An AC magnetic field can rotate a vortex-inolecule composed of two fractional vortices in a multiband type of multicomponent superconductor, where two components couple with each other through the intercomponent Josephson interaction. It may directly relate to an abnormal AC loss peak, which we have found recently in the multilayer cuprate supercondutor CuxBa2Ca2Cu3Oy (Cu-1223).