National Institute Of Materials Physics - Romania

Publications

830 articles found

701. Optical properties of 3,4,9,10-perylenetetracarboxylic dianhydride and 8-hydroxyquinoline aluminum salt films prepared by vacuum deposition

Authors: Stanculescu, A; Stanculescu, F; Tugulea, L; Socol, M

Published: 2006, ADVANCED MATERIALS FORUM III, PTS 1 AND 2, 514-516, 960, DOI: 10.4028/www.scientific.net/MSF.514-516.956

The main purpose of this paper is to investigate the optical properties of PTCDA and Alq3 films, prepared by two steps, vacuum evaporation and deposition processes on platelets of glass, quartz, and indium-tin-oxide (ITO) coated glass. We have emphasised the bands structure of the absorption spectra with peaks situated at 358 nm, 374 nm, 475 nm and 552 nm in PTCDA, respectively 232 nm, 261 nm and 380 nm in Alq3 that confirms the dominant presence of Alq3 meridianal molecular isomer. For PTCDA films deposited on glass coated with ITO, the structure of the weak double peak at low wavelength is partially modified, but the positions of the two important absorption peaks situated at 2.25 eV and 2.61 eV are unchanged. The two different luminescence emission peaks obtained in Alq3 for different excitation wavelengths (gimel=360 nm and gimel=520 nm) suggest the existence of the facial isomer beside the meridianal one. We have evidenced a significant Stocks shift in the spectra (Delta E-PTCDA=0.40 eV; Delta E-Alq3=0.9 eV) and a large Frank-Condon shift (0.40-2.3 eV), suggesting important effect associated respectively with the solid state structure and important conformational differences between the ground and excited state.

702. Spectroscopic studies on nanocomposites obtained by functionalization of carbon nanotubes with conducting polymers

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

Published: 2006, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 447, 403, DOI: 10.1080/15421400500385332

Vibrational properties of composites based on single-walled carbon nanotubes (SWNTs) and conducting polymers of the type polyaniline (PANI) and poly (3,4-ethylene dioxythiophene) (PEDOT) are reported. For PANI-functionalized SWNTs, the intensity increase of the Raman band at 178 cm(-1) , associated with radial breathing modes of SWNTs bundles, indicates an additional roping of nanotubes due to the presence of the polymer. The interaction of this composite with NH4OH solution involves an internal redox reaction between PANI and SWNTs. Thus, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. The functionalization of SWNT side walls with PEDOT is invoked as well.

703. Comparison of the luminescence properties of the x-ray storage phosphors BaCl2 : Ce3+ and BaBr2 : Ce

Authors: Selling, J; Corradi, G; Secu, M; Schweizer, S

Published: DEC 21 2005, JOURNAL OF PHYSICS-CONDENSED MATTER, 17, 8078, DOI: 10.1088/0953-8984/17/50/024

The single-crystalline x-ray storage phosphor BaCl2:Ce3+ has been investigated by photo- and x-ray luminescence, and also by observing the afterglow and the photostimulated luminescence (PSL). A single active Ce3+ site has been observed with a characteristic emission doublet at 349 and 373 nm at room temperature. The PSL stimulation spectrum shows a clear resemblance to F-type absorption spectra in undoped BaCl2, indicating that the PSL-active electron centres are F-type centres. The results are compared with previous photoluminescence, PSL and new x-ray luminescence data on BaBr2:Ce3+. The integral PSL efficiency in the chloride is found to be somewhat smaller than in the bromide, which is still large enough for storage phosphor applications, while the efficiency in the bromide may be even larger or comparable to that of the commercial x-ray storage phosphor BaFBr2:Eu2+.

704. SERS, FT-IR and photoluminescence studies on single-walled carbon nanotubes/conducting polymers composites

Authors: Lefrant, S; Baibarac, M; Baltog, I; Godon, C; Mevellec, JY; Wery, J; Faulques, E; Mihut, L; Aarab, H; Chauvet, O

Published: DEC 15 2005, SYNTHETIC METALS, 155, 669, DOI: 10.1016/j.synthmet.2005.08.026

Surface-enhanced Raman scattering (SERS), Fourier transform infrared (FT-IR) and photoluminescence (PL) spectroscopies were used to investigate composites based on single-walled carbon nanotubes (SWNTs) and different conducting polymers like polyaniline (PANI), polyparaphenylene vinylene (PPV) and poly 3-hexylthiophene (3-PHT). In the case of SWNTs/PANI, different composites are obtained by adding dispersed SWNTs powder to the polymer solutions and by chemical polymerization of aniline in presence of SWNTs. The difference originates in the irreversible chemical transformation of SWNTs in the polymerization medium. The synthesis medium used for the preparation of PANI transforms SWNTs in fragments of shorter length like closed-shell fullerenes. This explains the similarity of SERS and FT-IR spectra of the composites PANI/SWNTs and PANI/C-60, chemically synthesized. Electrochemical polymerization of aniline in an HCl solution on a SWNT film leads to a covalent functionalization of SWNTs with PANI. In this case, Raman scattering data suggest an additional nanombes roping with PANI as a binding agent. A post treatment with the NH4OH solution of polymer-functionalized SWNTs involves an internal redox reaction between PANI and carbon nanotubes. As a result, the polymer chain undergoes a transition from the semi-oxidized state into a reduced one. In the case of PPV and 3-PHT, the effect of the concentration of SWNTs on the photoluminescence properties will be described and compared, as probes of interaction. (C) 2005 Elsevier B.V. All rights reserved.

705. Coherent anti-Stokes Raman scattering on single-walled carbon nanotube thin films excited through surface plasmons

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

Published: DEC 2005, PHYSICAL REVIEW B, 72, DOI: 10.1103/PhysRevB.72.245402

We report experimental data that indicate an anti-Stokes Raman emission, reminiscent of coherent anti-Stokes raman scattering. It originates from a wave mixing process between the incident laser light (omega(l)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism. The variation of anti-Stokes SERS spectra of single-walled carbon nanotubes, copper phthalocyanine, and poly(bithiophene) as a function of the film thickness, the laser excitation intensity, and the numerical aperture of the microscopic objective used for collecting the scattered light demonstrate the described phenomenon.

706. Coherent anti-Stokes Raman scattering on single-walled carbon nanotubes and copper phthalocyanine thin films excited through surface plasmons

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

Published: NOV 2005, JOURNAL OF OPTICS A-PURE AND APPLIED OPTICS, 7, 639, DOI: 10.1088/1464-4258/7/11/003

Experimental data indicating an anti-Stokes Raman emission, reminiscent of coherent anti-Stokes Raman scattering (CARS), that originates in a wave-mixing process between the incident laser light (omega(1)) and Stokes Raman light (omega(s)) generated by a surface enhanced Raman scattering (SERS) mechanism are reported. The variation of anti-Stokes SERS spectra of single-walled carbon nanotubes (SWNTs) and copper phthalocyanine (CuPc) as a function of the film thickness, laser excitation intensity and numerical aperture of the microscopic objective used for collecting the scattered light are presented as experimental arguments.

707. X-ray absorption near edge structure of As2Se3 and As4Se4 thin amorphous films

Authors: Popescu, M; Sava, F; Aldea, N; Xie, YN; Hu, TD; Tao, L; Leonovici, M

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1806, DOI:

X-ray absorption spectroscopy has been used to get information on the structure of chalcogenide glasses. The data analysis was focused on the near edge X-ray absorption spectrum. The experimental As and Se K-edge absorption spectra of thin films of As2Se3 and As4Se4 have been measured in Beijing synchrotron at the beam line, using a double crystal monochromator with Si (111) crystals. The near-edge absorption curves were resolved in two components: the strong white line at the energy threshold and the first oscillatory part following the white line at approximately 7-8 eV above the K-edge, which undergoes changes in shape and position as a function of the modifications in the atomic structure induced by the change of composition. The XANES characteristic for the two types of films allows to conclude that the local disorder around As and Se is different. The non-stoichiometric composition, As4Se4, exhibits more disorder than the stoichiometric one.

708. Absorption and photoluminescence properties of Cds : Mn2+: Cu+ nanostructures

Authors: Sima, M; Enculescu, I; Ghiordanescu, V; Mihut, L

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 1955, DOI:

A layer of doped CdS nanocrystals was deposited on the surfaces of nanopores of polyethyleneterephtalate (PET) membranes. Optical absorption measurements were used to determine the bandgaps of the nanocrystals; CdS:Mn2+ and CdS:Mn2+:Cu+ show a blue and red shift, respectively, relative to the band gap of nanostructurated CdS. Photoluminescence spectra of the doped and undoped CdS samples exhibit wide bands covering the visible spectrum range.

709. Embedding Jacobsen manganese(III) salen complex into nanoporous molecular sieves: Spectroscopic characterisation of host-guest interactions

Authors: Frunza, L; Zgura, I; Nicolaie, I; Dittmar, A; Kosslick, H; Fricke, R

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2148, DOI:

We report some spectroscopic arguments showing the guest-host interactions in the case of the composites containing Jacobsen salen complex and nanoporous molecular sieves of different types: SBA-15, MCM-48, MCM-41. The complex was embedded by impregnation, but care was given for washing out the weakly anchored part. Siliceous nanoporous materials lead to a weaker interaction than A1 containing forms. Thermal analysis has shown that at least in the case of the composite containing MCM-41 the embedded complex still contain chloride ions, therefore the bonding to the surface was apical. In situ experiments indicate that the thermal stability of the embedded complex is higher than in the free state. The differences among the composites coming from the structure of the molecular sieves are discussed.

710. Fullerene and nanotubes based on arsenic networks. A modelling study

Authors: Zamfira, S; Popescu, M; Sava, F

Published: AUG 2005, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 7, 2034, DOI:

Arsenic is the main component of many chalcogenide glasses. Due to its triple co-ordination arsenic has the tendency to form two-dimensional networks in both crystalline and amorphous state. Besides the layered form of arsenic it exists molecular arsenic. Small molecules are characteristic to this form of arsenic. Large arsenic clusters have been not identified up to now in amorphous films. A modelling study was carried out in order to demonstrate the possibility to find or to prepare fullerene-like configurations based on arsenic as well as nanotubes (or nanowires) of various diameters.