National Institute Of Materials Physics - Romania

Publications

830 articles found

771. C-60-polymer nanocomposites: evidence for interface interaction

Authors: Giusca, C; Baibarac, M; Lefrant, S; Chauvet, O; Baltog, I; Devenyi, A; Manaila, R

Published: 2002, CARBON, 40, 1574, DOI: 10.1016/S0008-6223(02)00024-6

Polyaniline-fullerene (PA-C-60) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline-emeraldine base (PA-EB) and C-60, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C-60. The Raman bands peaking at 1330-1370 cm(-1). associated with a protonated structure Were used as indicative for changes of the PA-EB phonon spectrum resulting from C-60 doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (An or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C-60(-)) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA-C-60 reveals the existence of two polymeric structures: a doped PA (doped with C-60(-) ions) and an undoped one, the latter with a structure of 'pendant chain' type. Structural (XRD) data reveal the presence of C-60 nano-zones, with a lattice parameter increase of 0.3-0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an 'expanded' lattice. induced by ionic interface effects. (C) 2002 Elsevier Science Ltd. All rights reserved.

772. The stability of cadmium chalcogenide pigments in the process of laser cleaning of painted surfaces

Authors: Radvan, R; Popovici, N; Savastru, R; Ghica, C; Sava, F; Popescu, M

Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 902, DOI:

Pigments based on cadmium selenide sulphides and cadmium sulfides were analysed as regarding their structure and stability against the laser irradiation, a new technique for cleaning the painted surfaces in artwork restoration, The pulsed Nd:YAG laser radiation determines the effusion of some sulphur from the red pigment Cd(S,Se) and significant decrease of the average size of the crystallites. The color turns to dark red. For yellow pigment (CdS) no change of crystallite size was detected after laser irradiation.

773. PbSe1-xTex thick thermoelectric films obtained by electrochemical deposition from aqueous solutions

Authors: Nedelcu, M; Sima, M; Stoica, T; Manea, AS; Lazarescu, MF; Visan, T

Published: DEC 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 914, DOI:

It is presented a study of PbSe1-xTex thick films electrodeposition on glassy carbon and ITO electrodes in acid solutions (0.1M HNO3), using cyclic voltammetry and rotating-disk techniques. Electrochemical impedance spectroscopy study of PbSe1-xTex film in 0.1M HNO3 is reported.

774. Luminescence of oxidized porous silicon: Surface-induced emissions from disordered silica micro- to nanotextures

Authors: Fritsch, E; Mihut, L; Baibarac, M; Baltog, I; Ostrooumov, M; Lefrant, S; Wery, J

Published: NOV 1 2001, JOURNAL OF APPLIED PHYSICS, 90, 4782, DOI: 10.1063/1.1410887

The luminescence spectra of fully oxidized porous silicon show two broad bands and one vibronic structure between 2 and 3.3 eV, all excited at 340 or 275 nm (3.65 and 4.51 eV). Two of these structures have not been described previously. Interestingly, these emissions are found in other forms of amorphous or disordered silica with high specific surfaces: frosted silica glass, silica gel, even various natural opals. These emissions disappear when the surface is passivated. They are, therefore, attributed to surface-related defects. The vibronic structure involves a nearly free SiO4 tetrahedron. Another vibronic structure found only in some opals is attributed to the uranyl group. (C) 2001 American Institute of Physics.

775. Structure and properties of chalcogenide glasses in the system (As2S3)(1-x)(Sb2S3)(x)

Authors: Sava, F

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 432, DOI:

The glass system (As2S3)(1-x)(Sb2S3)(x), 0 less than or equal tox less than or equal to0.65, has been studied by X-ray diffraction and microhardness measurements. The long-time Irradiation of the samples by ultraviolet rays has been carried out and its structural effect was investigated. The substitutional model and the microphase separation model have been discarded. A new intermediate model, whose main feature is the formation of mezoscopic Sb2S3 clusters, has been advanced.

776. Visible light emission from Cd1-xMnxS nanocrystals

Authors: Ghiordanescu, V; Sima, M; Grecu, MN; Mihut, L

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 524, DOI:

The luminescence spectra of some Cd1-xMnxS nanocrystals have been measured at room and liquid nitrogen temperature. The Mn2+ ions give rise to a broad emission band centered at about 580 nm, between the emission bands of CdS host.

777. UV irradiation effects in pure and tin-doped amorphous AsSe films

Authors: Popescu, M; Iovu, M; Hoyer, W; Shpotyuk, O; Sava, F; Lorinczi, A

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 306, DOI:

Pure and tin-doped AsSe amorphous films were investigated. The changes in the MRO induced by Sn were analysed be accurate profiling the first sharp diffraction peak (FSDP) in the X-ray diffraction diagram. A shift of FSDP as a function of tin concentration was observed. The structural changes induced by ultraviolet rays (lambda = 336 nm) for various time intervals of irradiation were revealed by small angle X-ray diffraction. It was revealed the formation of a special layer at the surface of the films. whose thickness increases during UV irradiation.

778. Thermo and photoluminescence of silicate laser glass doped with neodymium

Authors: Grigoras, B; Cerchez, M; Ionescu, L; Secu, M; Matei, L; Trutia, A

Published: JUN 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 562, DOI:

The luminescence and thermoluminescence have been measured in vitreous materials doped with Nd3+. The luminescence spectra show a maximum at 400 nm and a shoulder at about 440 nm. The measured global thermoluminescence shows a broad band with a maximum at 270 degreesC, which suggest a continuous distribution of electron traps induced by ionizing radiation. Thermoluminescence measured through two optical filters which transmit at about 400 nm and 440 nm wavelength shows a structured behavior with two glow peaks at 270 degreesC and 330 degreesC. This apparently contradictory behavior has been explained by the existence in this material of a continuous distribution of tr ap levels and a discrete distribution of recombination levels. The 270 degreesC and 330 degreesC glow peaks have been interpreted as being due to recombination of the electrons released from electron traps with O2-. and Nd3+ hole centers. Due to the high stability of the defects induced by the radiation observed from thermoluminescence measurements, this material could be used as a new radiation detector.

779. SERS studies on disordered carbon nanotube thin films

Authors: Baibarac, M; Benoit, JM; Lefrant, S; Baltog, I; Schreiber, J; Bernier, P; Chauvet, O

Published: MAR 15 2001, SYNTHETIC METALS, 121, 1200, DOI: 10.1016/S0379-6779(00)00735-9

The SERS technique has been proved to be successful to study Single-Walled Carbon Nanotubes (SWNT's), with the observation of peculiar features. In this study, we present more specifically the Raman features which are strongly dependent on the morphology of the nanotube thin films, their thickness, the interfacial effects between films and support, the effect of solvent used to disperse the nanotubes onto the metallic surface.

780. Optical properties of polyaniline/CdS nanocrystals composite film

Authors: Ghiordanescu, V; Sima, M; Nedelcu, M; Giubelan, M

Published: MAR 2001, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 3, 93, DOI:

The optical spectra of CdS nanocrystals embedded in polyaniline matrix have been studied. The presence of surface states is revealed both in absorption and emission spectra. The polymer matrix determines a shift of the absorption edge of CdS nanocrystals, towards higher energies.