National Institute Of Materials Physics - Romania

Publications

839 articles found

571. ZnO particles of wurtzite structure as a component in ZnO/carbon nanotube composite

Authors: Baibarac, M; Baltog, I; Velula, T; Pasuk, I; Lefrant, S; Gautier, N

Published: NOV 4 2009, JOURNAL OF PHYSICS-CONDENSED MATTER, 21, DOI: 10.1088/0953-8984/21/44/445801

Composites based on carbon nanotubes and ZnO particles with needle shapes were prepared for applications in energy storage. Depending on the temperature (85 or 25 degrees C) at which the reaction between NaOH and ZnCl(2) was carried out, particles with two different morphologies: needle-shaped (NS) and double-pyramid-shaped (DPS), respectively, are obtained. Scanning electron microscopy, photoluminescence, UV-Vis absorption spectroscopy, x-ray diffraction and Raman light scattering studies reveal that the NS and DPS particles belong to ZnO with wurtzite (WZ) structure and epsilon-Zn(OH)(2) as precursors of ZnO, respectively. Using the ZnO/carbon nanotube composite as a negative electrode and an electrolytic solution containing LiPF(6), the charge-discharge characteristics of rechargeable lithium ions cells were determined. Additional information concerning the electrochemical reactions at the interface of the two electrodes was obtained by cyclic voltammetry.

572. Direct laser writing of two-dimensional photonic structures in amorphous As2S3 thin films

Authors: Popescu, A; Miclos, S; Savastru, D; Savastru, R; Ciobanu, M; Popescu, M; Lorinczi, A; Sava, F; Velea, A; Jipa, F; Zamfirescu, M

Published: NOV 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1880, DOI:

A method for building photonic structures in As2S3 amorphous chalcogenide films has been developed. 2-D photonic configurations characterized by a regular assembly of rods (triangular lattice) or gratings with traces of micrometer period have been obtained. A femto-second laser has been used in photonic crystal registration. The simulation performed on these photonic configuration shows that the obtained chalcogenide structures could be efficient for operation in the infrared range around several micrometers wavelength.

573. Silver/amorphous As2S3 heterostructure

Authors: Popescu, M; Sava, F; Lorinczi, A; Velea, A; Leonovici, M; Zamfira, S

Published: NOV 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1594, DOI:

The heterostructure Ag/As2S3 was deposited on glass substrate in two configurations: Ag/As2S3/glass and As2S3/Ag/glass. The effect of light emitted by a halogen lamp has been investigated by optical microscopy and X-ray diffraction. Particular morphological and structural aspects were revealed. Lateral diffusion rate of Ag has been determined.

574. Optical advanced spectroscopic techniques for the study of nano-structured materials: Applications to carbon nanotubes

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

Published: NOV 2009, SYNTHETIC METALS, 159, 2176, DOI: 10.1016/j.synthmet.2009.08.029

In this paper, we present the anti-Stokes Raman scattering as a technique allowing investigations of materials at a nanoscale level. When the energy of the excitation light coincides with the energy of an electronic transition, a strong anti-Stokes Raman spectrum with respect to the prediction of the Maxwell-Boltzman (MB) law is regularly observed. Under a tight-focusing of the excitation light, the anti-Stokes Raman emission is reminiscent of Coherent anti-Stokes Raman Scattering (CARS). It has been detected on carbon nanotubes (CNTs), prototypes of nanometric materials, as well as on other compounds such as copper phthalocyanine (CuPc), poly(bithiophene) (PBTh), poly(3,4-ethylene dioxythiophene) (PEDOT), polyparaphenylene vinylene (PPV) layered as thin films on a metallic support in which are generated surface plasmons. We demonstrate that nanostructures by themselves can be of importance by generating non-linear phenomena that can be exploited for studying such materials and in particular carbon nanotubes. (C) 2009 Elsevier B.V. All rights reserved.

575. Crystalline-amorphous and amorphous-amorphous transitions in phase-change materials

Authors: Popescu, M; Sava, F; Velea, A; Lorinczi, A

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1823, DOI: 10.1016/j.jnoncrysol.2009.04.053

The transition from the crystalline state to amorphous state and back has been studied in the particular case of the GeSb2Te4 phase-change material by a computer simulation procedure. Modelling at the nanoscale indicates specific structural characteristics, especially the multiplicity of the amorphous phase as opposite to the uniqueness of the crystalline phase. in the particular case of the Si(12)Ge(10)AS(30)Te(48) switching glass two types of ordering have been pointed out and characterized. (C) 2009 Elsevier B.V. All rights reserved.

576. Crystallization and spectroscopic properties of Eu-doped CaF2 nanocrystals in transparent oxyfluoride glass-ceramics

Authors: Secu, M; Secu, CE; Polosan, S; Aldica, G; Ghica, C

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1872, DOI: 10.1016/j.jnoncrysol.2009.04.062

Transparent oxyfluoride glass-ceramic in the system SiO2-Al2O3-CaF2-EuF2 containing Eu-doped CaF2 nanocrystals were produced by using the controlled crystallization of melt-quenched glass. X-ray diffraction and transmission electron microscopy data have revealed the formation of the CaF2 nanocrystals of about 65 nm size. Photoluminescence spectra have shown an increase of the splitting of the luminescences associated to the Eu3+ ion along with annealing time which is consistent with the Eu3+ environment evolving from a glassy to a crystalline state. (C) 2009 Elsevier B.V. All rights reserved.

577. A new model for the structure of chalcogenide glasses: The closed cluster model

Authors: Popescu, M; Sava, F; Lorinczi, A

Published: OCT 1 2009, JOURNAL OF NON-CRYSTALLINE SOLIDS, 355, 1819, DOI: 10.1016/j.jnoncrysol.2009.05.066

A new model is proposed for the structure of low atomic coordination chalcogenide glasses. The closed clusters model is based on the various types of clusters, packed by van der Waals forces in a molecular-type packing. Arguments are given to support the new model, taken as example the typical chalcogenide glass As2S3. (C) 2009 Elsevier B.V. All rights reserved.

578. Optical properties of CdS electrodeposited nanowires

Authors: Matei, E; Preda, N; Enculescu, M; Sima, M; Sima, M; Enculescu, I

Published: OCT 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1022, DOI:

Electrochemical deposition was performed in order to prepare CdS nanowires. The method employed for preparation of such high aspect ratio nanostructures was template replication. Ion track polycarbonate membranes were used as templates. The nanowires were studied by scanning electron microscopy (morphology characterization), energy dispersive X ray analysis (composition) and optical spectroscopy. Optical reflection spectroscopy was performed in order to determine the band gap value while photoluminescence spectroscopy was used for getting information regarding the point defects in the material.

579. Optical fiber coupling to a laser diode through chalcogenide microlenses

Authors: Velea, A; Rusu, M; Popescu, M

Published: OCT 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1383, DOI:

Microspherical lenses (50 divided by 800 mu m in diameter) based on glassy As(2)S(3), have been produced by a special flame melting technique. The microlenses have been used for focusing the red - infrared laser light at the end of an optical fiber. Microlens arrays have been produced and applied in coupling optical fibers to a light remitting diode (LED), in order to increase the intensity. A double ball lens coupling scheme has been designed and manufactured.

580. Surface Enhanced Raman Scattering Studies on Poly(3,4-ethylene dioxythiophene)/Single-Walled Carbon Nanotubes Composites and Their Application to Rechargeable Lithium Batteries

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

Published: OCT 2009, JOURNAL OF NANOSCIENCE AND NANOTECHNOLOGY, 9, 6209, DOI: 10.1166/jnn.2009.1548

In this paper, surface enhanced Raman scattering (SERS) studies on the chemical polymerization of 3,4-ethylene dioxythiophene (EDOT) in the presence of single-walled carbon nanotubes (SWNTs) are reported. Both a non-covalent and covalent functionalization of SWNTs with poly(3,4-ethylene dioxythiophene) (PEDOT) is invoked as a result of the following variations induced in the SERS spectra of PEDOT and SWNTs: (i) the appearance of a Raman line at 140 cm(-1) indicating the formation of a new covalent bond between PEDOT and SWNTs; (ii) an increase in the intensity of the Raman line at 705 cm(-1), associated with the deformation vibration mode of C-S-C bond, the result of a steric hindrance effect induced by the bonding of PEDOT on SWNTs; and (iii) the enhancement of the Raman band with maximum at 1540 cm(-1) (G(-) component) in SWNTs when the PEDOT weight in the PEDOT/SWNTs composite increases. Using the PEDOT/SWNTs composite as a positive electrode and an electrolytic solution containing LiPF6, the charge-discharge characteristics of the rechargeable lithium cells are determined. High specific discharge capacity are reported for the PEDOT/SWNTs composite (ca. 218 mAh g(-1)) in comparison with PEDOT doped with FeCl4- ions (ca. 25 mAh g(-1)).