National Institute Of Materials Physics - Romania

Publications

5714 articles found

3101. Synthesis of narrow diameter distribution carbon nanotubes on ZnO supported catalysts

Authors: Lupu, D; Biris, AR; Watanabe, F; Li, ZR; Dervishi, E; Saini, V; Xu, Y; Biris, AS; Baibarac, M; Baltog, I

Published: MAY 12 2009, CHEMICAL PHYSICS LETTERS, 473, 304, DOI: 10.1016/j.cplett.2009.03.069

Multiwall carbon nanotubes, as indicated by electron microscopy and spectroscopy, were grown over a novel Co(5 wt.%)/ZnO catalyst by using a cold wall radio-frequency catalytic chemical vapor deposition method. The nanotubes were found to have a rather narrow diameter distribution, which can be explained by the formation over the ZnO support particles of uniform Co clusters, as shown by high resolution transmission electron microscopy studies. The growth of carbon nanotubes over such a support could represent a fast and reliable method to develop in one step 3D ZnO-CNTs heterogeneous composites of any size or shape, for use in advanced applications. (c) 2009 Elsevier B.V. All rights reserved.

3102. Ambiguity in the statistics of single-component winding vortex in a two-band superconductor

Authors: Tanaka, Y; Crisan, A

Published: MAY 1 2009, PHYSICA B-CONDENSED MATTER, 404, 1039, DOI: 10.1016/j.physb.2008.11.011

There are four topologically different paths to interchange two single-component winding vortices in a two-band superconductor having a weak inter-band interaction, where each band has its own superconducting component and its own phase, theta(v), other than the ordinary quantum phase, Theta (v is the index of the band and Theta is defined at the region of theta(1) = theta(2).). The acquired phase for the interchange of two single-winding vortices depends on the path, and three values Theta(soliton),-Theta(soliton) and 0, are observed. Theta(soliton) is the phase-slip accompanying the inter-band phase difference soliton (i-soliton). The interchange requires the creation and annihilation of the i-soliton and gives rise to an ambiguity in the statistics. (C) 2008 Elsevier B.V. All rights reserved.

3103. Origin of the X-ray magnetic circular dichroism at the L-edges of the rare-earths in RxR ' Al-1-x(2) systems

Authors: Chaboy, J; Laguna-Marco, MA; Piquer, C; Boada, R; Plugaru, N; Maruyama, H; Kawamura, N

Published: MAY 2009, JOURNAL OF SYNCHROTRON RADIATION, 16, 412, DOI: 10.1107/S0909049509009807

An X-ray magnetic circular dichroism (XMCD) study performed at the rare-earth L-2,L-3-edges in the RxR'Al-1-x(2) compounds is presented. It is shown that both R and R' atoms contribute to the XMCD recorded at the L-edges of the selected rare-earth, either R or R'. The amplitude of the XMCD signal is not directly correlated to the magnetization or to the value of the individual (R, R') magnetic moments, but it is related to the molecular field acting on the rare-earth tuned in the photoabsorption process. This result closes a longstanding study of the origin of the XMCD at the L-edge of the rare-earths in multi-component systems, allowing a full understanding of the exact nature of these signals.

3104. Stand-alone cosmic muon reconstruction before installation of the CMS silicon strip tracker

Authors: Adam, W; Bergauer, T; Dragicevic, M; (...) Lungu, GA; (...) Tsang, KV (CMS Tracker Collaboration)

Published: MAY 2009, JOURNAL OF INSTRUMENTATION, 4, P05004, DOI: 10.1088/1748-0221/4/05/P05004

The subsystems of the CMS silicon strip tracker were integrated and commissioned at the Tracker Integration Facility (TIF) in the period from November 2006 to July 2007. As part of the commissioning, large samples of cosmic ray data were recorded under various running conditions in the absence of a magnetic field. Cosmic rays detected by scintillation counters were used to trigger the readout of up to 15% of the final silicon strip detector, and over 4.7 million events were recorded. This document describes the cosmic track reconstruction and presents results on the performance of track and hit reconstruction as from dedicated analyses.

3105. Magnetic properties of NiCu thin films obtained by electrodeposition

Authors: Bazavan, D; Bazavan, R; Enculescu, I; Matei, E; Necula, C; Ion, L; Antohe, S

Published: MAY 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 488, DOI:

Using an electrochemical method have been produced NiCu thin films for magnetic applications. The recent development of first-order reversal curve (FORC) diagrams has allowed the detailed investigation of coercivity spectra, interaction and domain states of magnetic thin films. Their magnetic properties have been investigated by Micro Mag (TM) 3900 Vibrating Sample Magnetometer (VSM) and are discussed.

3106. In-depth investigation of EPR spectra of Mn2+ ions in ZnS single crystals with pure cubic structure

Authors: Nistor, SV; Stefan, M

Published: APR 8 2009, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, DOI: 10.1088/0953-8984/21/14/145408

The X (9.8 GHz)-band electron paramagnetic resonance (EPR) properties of substitutional Mn2+ ions in high quality cubic ZnS single crystals grown from PbCl2 flux have been thoroughly investigated. Accurate spin Hamiltonian (SH) parameters: g = 2.002 25 +/- 0.000 06; a = (7.987 +/- 0.008) x 10(-4) cm(-1) and A = -(63.88 +/- 0.02) x 10(-4) cm(-1) were obtained by simulation and fitting to the experimentally allowed transitions recorded for the magnetic field aligned within +/- 0.25 degrees along the main crystal axes. The normally forbidden hyperfine M = + 1/2 <->-1/2, Delta m = +/- 1 transitions were also observed. Their position was found to be in agreement, within the experimental accuracy of Delta H = +/- 0.01 mT, with calculations using the same SH parameters. The angular variation of the ratios of the intensities of the central forbidden to the allowed transitions could be accounted for only by including an additional constant contribution. The observed line broadening of the M = +/- 1/2 <->+/- 3/2 and +/- 3/2 <->+/- 5/2 fine structure transitions and their line width variation in a (110) plane have been quantitatively described by considering a random distribution of lattice strains at the Mn2+ impurity ions. The influence of the forbidden transitions and line broadening on the EPR spectra line shape of the Mn2+ ions in cubic ZnS crystalline powders is also examined.

3107. Transesterification of vegetable oils on basic large mesoporous alumina supported alkaline fluorides-Evidences of the nature of the active site and catalytic performances

Authors: Verziu, M; Florea, M; Simon, S; Simon, V; Filip, P; Parvulescu, VI; Hardacre, C

Published: APR 1 2009, , DOI: 10.1016/j.jcat.2009.01.012

3108. Photoluminescence and Raman spectroscopy studies on polyaniline/PbI2 composite

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: APR 2009, JOURNAL OF SOLID STATE CHEMISTRY, 182, 835, DOI: 10.1016/j.jssc.2009.01.007

Functionalization of PbI2 with conjugated polymers (polyaniline-emeraldine base (PANI-EB) or polyaniline-emeraldine salt (PANI-ES)) is demonstrated by Raman and luminescence studies. PbI2/PANI hybrid material was prepared by electrochemical polymerization of aniline onto the PbI2 modified Pt electrode and mechanico-chemical reaction between the two constituents. PANI interacting with the PbI2 gives rise to new Raman bands at 80,144 and 170 cm(-1). First line reveals the formation of "stacking faults" that disrupt the I-Pb-I layers stacking along the c axis by the insertion of polymer molecules. The bands at 144 and 170 cm(-1) are attributed to the vibrational mode associated with Pb-NHR ''(2) (R '' = C6H4) bond. The functionalization of PbI2 with PANI-EB brings forth the PANI-ES form. Depending on the semiconducting (PANI-EB) or conducting (PANI-ES) properties of the polymer in the PbI2/PANI intercalated material, a partial or total collection of the charges generated under band to band irradiation is revealed by photoluminescence studies. (C) 2009 Elsevier Inc. All rights reserved.

3109. Raman spectroscopic evidence for interfacial interactions in poly(bithiophene)/single-walled carbon nanotube composites

Authors: Baibarac, M; Baltog, I; Lefrant, S

Published: APR 2009, CARBON, 47, 1398, DOI: 10.1016/j.carbon.2009.01.031

Electrochemical polymerization of 2,2'-bithiophene (BTh) on single-walled carbon nanotube (SWCNT) films has been studied by Raman scattering and infrared absorption spectroscopy. Covalent functionalization of SWCNTs with poly(bithiophene) (PBTh) in its un-doped and doped states is demonstrated. The occurrence of a charge transfer process at the interface of PBTh and SWCNTs, is shown by: (i) an up-shift of the Raman lines associated with the radial breathing modes of SWCNTs that reveals both a doping process and an additional twisting together as a rope with the conducting polymer as binding agent; (ii) a new Raman band in the range 1430-1450 cm(-1) indicating the functionalization of SWCNTs with PBTh in doped and un-doped states; (iii) strong absorption bands situated in the interval 600-800 cm(-1) resulting from steric hindrance produced by the nanotube binding to the polymeric chain. Treatment of the PBTh/SWCNT composite with aqueous NH4OH Solution forms un-doped PBTh covalently functionalized SWCNTs. At the resonant excitation of the metallic tubes, an additionally enhanced Raman process is generated by plasmon excitation in the metallic nanotubes. It is evidenced by a particular behavior in the Stokes and anti-Stokes branch of the PBTh Raman line at 1450 cm(-1). (C) 2009 Elsevier Ltd. All rights reserved.

3110. Band ferromagnetism in systems of variable dimensionality II: the two-dimensional finite-temperature case

Authors: Lungu, GA; Teodorescu, CM

Published: APR 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, DOI:

In a previous paper [C.M. Teodorescu and G.A. Lungu, J. Optoelectron. Adv, Mater. 10, 3058 (2008)] we studied the zero temperature problem of the occurence of band ferromagnetism and of the derivation of the Stoner criterion for systems of variable dimensionality: 1D, 2D, 3D. The dimensionality of the system is reflected by a different shape of the density of states. For ideal 2D systems, the density of states is a constant and this seems to be the simplest case to be modelled. In this paper we integrate to this simplest model of constant density of states the influence of temperature, in order to analyse temperature-dependent ferromagnetism in two-dimensional systems, such as magnetic surfaces. Some surprising results are obtained, namely: (i) in contrast to the common belief, in this case the influence of the temperature is to favour, not to inhibit ferromagnetism, i.e. in some conditions ferromagnetism may be obtained at finite temperature. even for systems where the zero temperature Stoner criterion is not satisfied; (ii) for a careful choice of the ratio between the Hubbard energy parameter U and the equilibrium zero-temperature Fermi level value epsilon(mu) (0), systems nonmagnetic at low temperature which become magnetic at higher temperature may be possible. A short review of the experimental data which may be interpreted within the present formalism is also given.