National Institute Of Materials Physics - Romania

Publications

839 articles found

491. Influence of Al doping agents nature on the physical properties of Al:ZnO films deposited by spin-coating technique

Authors: Ghomrani, FZ; Iftimie, S; Gabouze, N; Serier, A; Socol, M; Stanculescu, A; Sanchez, F; Antohe, S; Girtan, M

Published: MAR 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 251, DOI:

In this paper we present the morphological, structural, optical and electrical properties of aluminium doped zinc oxide films prepared by spin coating technique from a zinc acetate dihydrate and 2-methoxyethanol (0.5M) solution. AlCl3 and Al(NO3)(3) were used as doping agents in different concentrations (1at%, 4at% and 6at% in starting solution). After deposition, films were dried at 100 degrees C and then annealed at temperatures between 400 degrees C and 500 degrees C. The characterization of deposited layer was performed by Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM) and UV-Vis spectroscopy. The results show that the optical and electrical properties of the structures strongly depend on the deposition conditions of ZnO:Al. In addition, the resistivity can be easily varied depending on ZnO:Al annealing temperatures and Al concentration.

492. Preparation of graphene and its application in dye-sensitized solar cells

Authors: Sima, M; Enculescu, I; Sima, A

Published: MAR 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 418, DOI:

Graphene sheets were prepared using electrochemical and chemical steps followed graphite electrochemical oxidation, graphite chemical oxidation, ultrasound expholiation and chemical reduction of carbon material. Films of graphene were electrophoretically deposited from aqueous dispersion on FTO electrode. These films were tested as cathode for a dye-sensitized solar cell. The morphology of the prepared products was imaged by scanning electron microscopy; the intermediate compound, graphene oxide was characterized by IR spectroscopy.

493. Electrochemical functionalisation of SWNTs with poly(3,4-ethylenedioxythiophene) evidenced by anti-Stokes/Stokes Raman spectroscopy

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

Published: MAR 2011, JOURNAL OF RAMAN SPECTROSCOPY, 42, 312, DOI: 10.1002/jrs.2705

The capability of anti-Stokes/Stokes Raman spectroscopy to evaluate chemical interactions at the interface of a conducting polymer/carbon nanotubes is demonstrated. Electrochemical polymerisation of the monomer 3,4-ethylenedioxythiophene (EDOT) on a Au support covered with a single-walled carbon nanotube (SWNT) film immersed in a LiClO4/CH3CN solution was carried out. At the resonant optical excitation, which occurs when the energy of the exciting light coincides with the energy of an electronic transition, poly(3,4-ethylenedioxythiophene) (PEDOT) deposited electrochemically as a thin film of nanometric thickness on a rough Au support presents an abnormally intense anti-Stokes Raman spectrum. The additional increase in Raman intensity in the anti-Stokes branch observed when PEDOT is deposited on SWNTs is interpreted as resulting from the excitation of plasmons in the metallic nanotubes. A covalent functionalisation of SWNTs with PEDOT both in un-doped and doped states takes place when the electropolymerisation of EDOT, with stopping at +1.6 V versus Ag/Ag+, is performed on a SWNT film deposited on a Au plate. The presence of PEDOT covalently functionalised SWNTs is rationalised by (1) a downshift by a few wavenumbers of the polymer Raman line associated with the symmetric C-C stretching mode and (2) an upshift of the radial breathing modes of SWNTs, both variations revealing an interaction between SWNTs and the conjugated polymer. Raman studies performed at different excitation wavelengths indicate that the resonant optical excitation is the key condition to observe the abnormal anti-Stokes Raman effect. Copyright (C) 2010 John Wiley & Sons, Ltd.

494. Polydiphenylamine/carbon nanotube composites for applications in rechargeable lithium batteries

Authors: Baibarac, M; Baltog, I; Lefrant, S; Gomez-Romero, P

Published: FEB 15 2011, MATERIALS SCIENCE AND ENGINEERING B-ADVANCED FUNCTIONAL SOLID-STATE MATERIALS, 176, 120, DOI: 10.1016/j.mseb.2010.10.008

Polydiphenylamine/single walled carbon nanotube (PDPA/SWNT) composites were synthesized electrochemically aiming at their application as active electrode materials for rechargeable lithium batteries. The electrochemical polymerization of diphenylamine (DPA) on a SWNT film immersed in a 1 M HCl solution was studied by cyclic voltammetry. Comparing cyclic voltammograms recorded on a blank Pt electrode with those obtained for a SWNT film deposited on Pt electrode one observes in the latter case a decrease of the DPA reduction potential. To elucidate electrochemical polymerization mechanism, photoluminescence studies on DPA/SWNT and PDPA/SWNT systems were carried out. Additional information concerning the functionalization process of SWNT with PDPA was obtained by Raman and IR spectroscopy. Using the PDPA/SWNT composite as active material for the positive electrode of a rechargeable lithium cell (LiPF(6) electrolyte), the charge-discharge tests show a specific discharge capacity of ca. 245 mA h g(-1), much higher than the 35 mA h g(-1) for pure PDPA. (C) 2010 Elsevier B.V. All rights reserved.

495. Heat transfer process during the crystallization of benzil grown by the Bridgman-Stockbarger method

Authors: Barvinschi, F; Stanculescu, A; Stanculescu, F

Published: FEB 15 2011, JOURNAL OF CRYSTAL GROWTH, 317, 27, DOI: 10.1016/j.jcrysgro.2010.11.028

The temperature distribution and solid-liquid interface shape during benzil growth have been studied both experimentally and numerically. The heat transfer equation with appropriate boundary conditions has been solved by modelling a vertical Bridgman-Stockbarger growth configuration. Two models have been developed, namely a global numerical model and a pseudo-transient approximation in an ideal configuration. (C) 2010 Elsevier B.V. All rights reserved.

496. Pulsed laser deposition of semiconducting crystalline double-doped barium titanate thin films on nickel substrates

Authors: Apostol, I; Stefan, N; Luculescu, CR; Birjega, R; Socol, M; Miroiu, M; Mihailescu, IN

Published: FEB 1 2011, APPLIED SURFACE SCIENCE, 257, 3576, DOI: 10.1016/j.apsusc.2010.11.078

We synthesized by pulsed laser deposition (Ba,Sr,Y)TiO3 and (Ba,Pb,Y)TiO3 thin films on mechanically polished nickel substrates. The synthesized thin films were analyzed for: crystalline structure by X-ray diffractometry, morphology and surface topography by atomic force microscopy, optical and scanning electron microscopy, and elemental composition by energy dispersive X-ray spectroscopy and electrical properties by electrical measurements. We have shown that film properties were determined by the dopants, target composition, and deposition parameters (oxygen pressure, substrate temperature and incident laser fluence). All films exhibited a semiconducting behavior, as proved by the decrease of electrical resistance with heating temperature. (C) 2010 Elsevier B. V. All rights reserved.

497. Structural changes during the crystallization of the Bi4Ge3O12 glasses

Authors: Polosan, S; Nastase, F; Secu, M

Published: FEB 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 1113, DOI: 10.1016/j.jnoncrysol.2010.10.016

Bismuth-germanate glass ceramics with the composition 40% Bi2O3-60% GeO2 (in molar percents) were prepared through controlled crystallization of melt-quenched glass. The Raman and FTIR spectra recorded in the as-made glasses show broad bands at 240, 400, 780 cm(-1) and 400, 745 cm(-1) have been assigned Ge-O bonds which appear right after preparation. X-ray diffraction has shown that the as-made glasses are amorphous, but after annealing above the crystallization temperature at 558 degrees C, BGO nano-crystallites with a size of about 50 nm precipitate in the glass matrix. The Raman and FTIR spectra reveal sharp peaks associated to the "internal" and "external vibrations" of GeO4 tetrahedral groups inside the BGO nano-crystallites. In the glass ceramic sample the transparency region is shifted at longer wavelengths compared to as-made glass, due to the Rayleigh scattering on the BGO nano-crystallites. (C) 2010 Elsevier B.V. All rights reserved.

498. Eu3+-doped CaF2 nanocrystals in sol-gel derived glass-ceramics

Authors: Secu, M; Secu, CE; Ghica, C

Published: FEB 2011, OPTICAL MATERIALS, 33, 617, DOI: 10.1016/j.optmat.2010.11.016

Glass-ceramics containing Eu3+-doped CaF2 nanocrystals of about 16 nm size have been made using the controlled crystallization at higher temperatures of the Eu3+-doped CaF2-SiO2 xerogels. In the glass-ceramic material the Eu3+ ions are embedded in both silica network and in the non-centrosymmetric sites of the CaF2 nanocrystals structure. Lower phonon energy of CaF2 and the dehydratation processes reduce the probability of non-radiative de-excitations and as a result a luminescence enhancement and an increase of the PL lifetime is observed. Eu-doping modifies the traps distribution within the glass-ceramics and as a result an additional broad thermoluminescence peak at about 380 degrees C was observed. The peak was assigned to the recombination of the electrons thermal released from the Eu3+-related traps in the glass matrix and in the CaF2 nanocrystals. (C) 2010 Elsevier B.V. All rights reserved.

499. Tailoring immobilization of immunoglobulin by excimer laser for biosensor applications

Authors: Sima, F; Axente, E; Ristoscu, C; Mihailescu, IN; Kononenko, TV; Nagovitsin, IA; Chudinova, G; Konov, VI; Socol, M; Enculescu, I; Sima, LE; Petrescu, SM

Published: FEB 2011, JOURNAL OF BIOMEDICAL MATERIALS RESEARCH PART A, 96A, 394, DOI: 10.1002/jbm.a.32991

The sheltered transfer and immobilization of rabbit anti-human antiserum immunoglobulin G (IgG) by matrix-assisted pulsed laser evaporation (MAPLE) are reported. The iced targets submitted to laser irradiation consisted of 0.2-2 mg/mL IgG blended or not with lipid (L-a-phosphatidylcholine dipalmitoyl) dissolved in distilled water-based saline buffer. Thin IgG coatings were obtained at room temperature onto glass, fused silica, or silicon substrates. Ten thousand subsequent laser pulses of 0.33, 0.5, or 0.67 J/cm(2) fluence were applied for the synthesis of each sample. Morphology and composition of the thin films were studied by optical, scanning, and atomic force microscopy and Fourier transformed infrared spectrometry. Optical labeling methods such as spectrofluorimetry and fluorescence microscopy were selected to verify the biosensor transduction principle because of their high sensitivity for detecting low amounts of antigen (IgG). Protein immobilization to the substrate surface was demonstrated for all obtained structures after immersion in the donkey anti-rabbit secondary antibody solution. The IgG transfer and immobilization onto substrates were improved by addition of lipid to MAPLE solutions. (C) 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 96A: 384-394, 2011.

500. Hybrid organic-inorganic materials based on poly(o-phenylenediamine) and polyoxometallate functionalized carbon nanotubes

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

Published: JAN 31 2011, JOURNAL OF MOLECULAR STRUCTURE, 985, 218, DOI: 10.1016/j.molstruc.2010.10.044

The chemical polymerization of o-phenylenediamine (OPD) on single-walled carbon nanotubes (SWCNTs) in the presence of phosphomolybdic acid (H3PMo12O40 xH(2)O) has been studied by surface enhanced resonant Raman scattering (SERRS) spectroscopy. One demonstrates that an organic-inorganic hybrid composite of the type poly(o-phenylenediamine)/polyoxometallate-functionalized SWCNTs is produced by the chemical interaction between polyoxometallate-functionalized SWCNTs and poly(o-phenylenediamine) (POPD) doped with [H2PMo12O40](-) ions. According to TEM investigations, a result of the chemical interaction of SWCNT with H3PMo12O40 xH(2)O is the formation into the composite mass of tube fragments of shorter length, which behave like closed shell fullerenes since Raman fingerprint is given by lines situated at 240-275 and 1450-1472 cm(-1). The chemical polymerization of OPD on SWCNTs achieved in the absence of H3PMo12O40 xH(2)O leads to a covalent functionalization of the wall side of the tubes, which is revealed in Raman spectra, recorded at the excitation wavelength of 514 nm, by an enhancement of the lines associated with the tangential vibrational modes of SWCNTs. Using FTIR spectroscopy, significant hindrance steric effects are evidenced in the POPD/polyoxometallate-functionalized SWCNT composite. (c) 2010 Elsevier B.V. All rights reserved.