National Institute Of Materials Physics - Romania

Publications

5781 articles found

3481. Particular signature of isolated and bundled carbon nanotubes in their Raman spectra

Authors: Husanu, M; Baibarac, M; Baltog, I

Published: 2008, ROMANIAN REPORTS IN PHYSICS, 60, 699, DOI:

The efficiency of different surfactants (anionic, cationic, neutral) as chemical agents favoring in the unbinding of nanotube bundles in isolated entities is investigated by Raman and UV-VIS-NIR spectroscopy. ne neutral surfactants Tween 20 - polyoxyethylene sorbitan monolaurate (T-20-PSM) and Tween 80 - polyoxyethylene (80) sorbitan monooleate (T-80-PSM) have been found the most efficient. The isolated single walled carbon nanotubes (SWNTs) nanotubes are apprised at lambda(exc) = 1064 nm by two simultaneous modifications of the Raman spectra: i) narrowing of the band associated to the transversal vibration modes, i.e., G band (similar to 1592 cm(-1)); ii) change of shape of the complex band associated to the radial vibration modes (RBM) consequent on the decrease of the intensity of the components associated with the bundled nanotubes. The individualization of nanotubes is evidenced also in the UV-VIS-NIR absorption spectra by the appearance of a fine structure in the wide absorption band (similar to 1400-1750 nm) that is associated with the transitions E-S(11) of semiconducting SWNTs. The fine structure grows gradually with the separation degree in isolated nanotubes entities.

3482. Vortex Dynamics in Hg-based Multi- and Super-Multi-Layered Cuprates

Authors: Crisan, A; Tanaka, Y; Iyo, A; Matsuhata, H; Shivagan, DD; Shirage, PM; Button, TW; Abell, JS; Tokiwa, K; Watanabe, T

Published: 2008, 8TH EUROPEAN CONFERENCE ON APPLIED SUPERCONDUCTIVITY (EUCAS'07), 97, DOI: 10.1088/1742-6596/97/1/012013

Hg-based multi- and super-multi-layered cuprates HgBa2Can-1CunOy (Hg:12(n-1)(n)) (n >= 4) are composed of the charge reservoir layer (CRL) HgBa2Ox, and of CuO2 planes: outer planes (OP) with pyramidal oxygen coordination and inner planes (IP) with square oxygen coordination, with different charge distribution. This fact gives rise to very interesting phenomena, like coexistence of superconductivity (SC) in OPs with antiferromagnetism (AF) in IPs in Hg:1245. The dependence of T-c on the number n of CuO2 planes is also interesting: for n increasing from 4 to 5 and to 6, T-c decrease from 125 to 108 and then to about 103 K; further increase in n keeps T-c constant at about 103 K. In Hg:1245 we show that the AF ordering at T-N of 60 K has no influence on vortex dynamics, and there is a quite robust c-axis supercurrent. Vortex melting lines of various samples showed that Hg-based multi- layered cuprates (n = 4, 5) behaves in the usual way (increasing n resulted in decrease of Josephson coupling (JC) and a less sharp melting line) and are well described by the usual anisotropic GL-based theory. Samples with n >= 6 have all the same melting line, suggesting that, in this case, the short-range JC becomes much less important than the long-range magnetic coupling (MC). However, since the JC between two pancakes in OPs of adjacent unit cells (pancakes separated by the thin CRL) is large, we suggest that the vortex matter in Hg-based super-multilayered cuprates is composed of magnetically-coupled pancake-vortex-molecules.

3483. Spectroscopic characteristics of Tm3+ in Tm and Tm, Nd, Yb : Sc2O3 ceramic

Authors: Lupei, V; Lupei, A; Gheorghe, C; Ikesue, A

Published: MAY-JUN 2008, JOURNAL OF LUMINESCENCE, 128, 904, DOI: 10.1016/j.jlumin.2007.12.012

The spectroscopic investigation of Tm3+ or (Nd, Yb, Tm)-doped Sc2O3 transparent ceramics, as laser-active media for visible and IR emission, was performed. The spectra are dominated by Tm3+ ions in sites of C-2 symmetry and an energy level scheme and other spectral parameters were determined. The strong concentration quenching of H-3(4) level emission in Tm:Sc2O3 at 300 K is discussed by considering the resonant cross-relaxation (H-3(4)-> F-3(4))-(H-3(6)-> F-3(4)) process and multipolar interactions of various orders. The main energy-transfer processes leading to the blue upconversion emission from the (1)G(4) Tm3+ level in (Tm, Nd, Yb):Sc2O3 ceramic, under pulsed pumping at 808.3 nm were evidenced. (c) 2008 Elsevier B.V. All rights reserved.

3484. Smart soluble grafted polysiloxanes with potential applications in waterborne paints

Authors: Nor, I; Moleavin, I; Ibanescu, C; Sandu, V; Hurduc, N

Published: MAY-JUN 2008, ENVIRONMENTAL ENGINEERING AND MANAGEMENT JOURNAL, 7, 342, DOI:

The synthesis of some grafted polysiloxane and azo-polysiloxanes with potential applications as rheology modifiers or surfactants for waterborne paints is reported. Nowadays it became very important to design environmentally friendly systems exhibiting the best end-uses properties. Due to their complex architecture and their sensitivity to UV radiation the studied polymeric systems exhibit very interesting rheological properties. All the polymers containing the azobenzenic groups in the side chains tire able to interact with the UV/VIS light, due to the photo-isomerization processes. Due to this property, the azo-based polymers are able to generate photo-stimuli response accomplished by strong supramolecular properties modifications.

3485. ELECTROCATALYSTS AND ELECTRODE DESIGN FOR BIFUNCTIONAL OXYGEN/AIR ELECTRODES

Authors: Nikolova, V; Iliev, P; Petrov, K; Vitanov, T; Zhecheva, E; Stoyanova, R; Valov, I; Stoychev, D

Published: 2008, FUNCTIONALIZED NANOSCALE MATERIALS, DEVICES AND SYSTEMS, +, DOI: 10.1007/978-1-4020-8903-9_22

Electrocatalysts and appropriate electrode designs have been Studied with respect to the development of Bifunctional Air/Oxygen Electrode (BAE). Three groups of catalysts have been prepared: (i) CUxCo3-xO4; (ii) thin films of Co-Ni-Te-O and Co-Te-O and (iii) CoxOv/ZrO2 films. Different catalysts deposited on classical and originally designed GDE were compared by their electrochemical performances.

3486. Influence of polyvinylpyrolidone as an additive in electrochemical preparation of ZnO nanowires and nanostructured thin films

Authors: Enculescu, I; Matei, E; Sima, M; Enculescu, M; Sima, M; Ghica, C

Published: MAR-APR 2008, SURFACE AND INTERFACE ANALYSIS, 40, 560, DOI: 10.1002/sia.2749

Preparation of ZnO in different nano-morphological forms became a hot topic during the last few years. This tendency was motivated by the wide field of potential applications ranging from optics to electronics and spintronics. In the present work, we deal with the preparation of ZnO nanowires and nanostructured thin films using electrochemical deposition. ZnO nanowires were grown using the template approach, namely by replicating the nanopores of polycarbonate ion track membranes. The method yields uniform arrays of nanowires with the morphology controlled by the shape and size of the templates pores. Adding polyvinylpyrolidone as an additive in the growth bath became a necessity due to the fact that polycarbonate ion track membranes are usually hydrophobic and thus filling of the nanopores with the growth electrolyte is rather difficult. In order to better understand the influence of the additive on the electrochemical deposition of such nanostructures, similar experiments were performed for the deposition of ZnO thin films. Scanning electron microscopy, X-ray diffraction and optical spectroscopy measurements were performed for characterization of the deposited structures. Copyright (c) 2008 John Wiley & Sons, Ltd.

3487. Comparison between PZT thin films deposited on stainless steel and on platinum/silicon substrate

Authors: Stancu, V; Sava, F; Lisca, M; Pintilie, L; Popescu, M

Published: 2008, INTERFACIAL NANOSTRUCTURES IN CERAMICS: A MULTISCALE APPROACH, 94, DOI: 10.1088/1742-6596/94/1/012012

Pb(Zr1-xTix)O-3 (PZT) thin films were prepared by sol-gel method on stainless steel (SS) and on platinum-coated silicon substrate (Pt/Si). The structure revealed by X-ray diffraction shows strong crystallographic orientation: (110) and (100), respectively. The crystallite size shows significant differences: d((00l))((SS))= 27.1 nm, d((h00))((Pt)) = 88 nm. The tetragonal splitting is (Delta c/c)((ss))=3.55 % and (Delta c/c)((pt))=3.32 %. The ferroelectric hysteresis loop in the static mode is characterized by remanentpolarization of 25 mu C/cm(2) and coercive field of 45 kV/cm for SS substrate, while for Pt/Si substrate the values are 10 mu C/cm(2) and 39 kV/cm, respectively. The leakage current is about 3 orders of magnitude lower in the PZT film deposited on SS. The better properties of the PZT deposited on SS are explained by the presence of large single crystal-like crystallites, which make the film closer to epitaxial ones. The results show the potential of growing epitaxial films on low-price substrates such as stainless-steel.

3488. Correlational analysis of superconducting mixed copper oxides

Authors: Zarioiu, C; Lascu, VG; Petrova, L; Novac, A

Published: 2008, MATHEMATICS AND COMPUTERS IN BIOLOGY AND CHEMISTRY, +, DOI:

A unifying structural scheme of all layered superconducting cuprates is proposed. The paper is a review based on a three level correlational analysis of the behaviour of one compound, of a homologous series and a third interseries analysis, revealing multiple correlation between the critical temperature value and different bond lengths via the oxygen content.

3489. Silver quantum dots deposited on YAG coated silicon wafer

Authors: Popescu, M; Sava, F; Lorincz, A; Daroczi, L; Kokenyesi, S; Mihailescu, IN; Socol, G

Published: 2008, ROMANIAN REPORTS IN PHYSICS, 60, 787, DOI:

Silver nano-dots have been deposited by a special procedure on the surface of a YAG coated silicon wafer. Sizes of 40-100 nm and a self-organized distribution according to the pattern of the pattern of defects (dislocations, terraces, etc.) on the wafer's surface were revealed. The procedure is simple and can be applied for the controlled deposition of small silver clusters to be used both in medicine and in nano-electronic devices.

3490. InN Thin Films Deposition by rf Magnetron Sputtering

Authors: Braic, MT; Zoita, CN; Braic, VT; Toacsan, MI; Ioachim, AT

Published: 2008, 2008 33RD INTERNATIONAL CONFERENCE ON INFRARED, MILLIMETER AND TERAHERTZ WAVES, VOLS 1 AND 2, +, DOI:

InN thin films were grown by reactive magnetron sputtering in a UHV system, using Ar and N-2 as working gases. Electrical and optical investigations of the films were correlated with their structural and morphological characteristics in order to obtain good quality films for THz applications.