National Institute Of Materials Physics - Romania

Publications

5781 articles found

3101. Nitridation and crystallization of titanium oxynitride by thermal treatment of TiO2-anatase films in NH3

Authors: Trapalis, C; Calderon-Moreno, JM; Todorova, N; Teodorescu, VS; Stoica, M; Nicolescu, M; Anastasescu, M; Gartner, M; Zaharescu, M

Published: NOV 2009, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 11, 1814, DOI:

Nitrogen is often used for doping TiO2 films to improve their photocatalytic properties in visible light. Multilayer TiO2 anatase films were deposited by sol-gel method on quartz substrate and thermally treated in O-2 and NH3 flow in 500-800 degrees C range. The effect of the annealing treatment (temperature and atmosphere) on the structural properties of TiO2 films was studied by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). Nitridation causes the amorphization of the anatase tetragonal phase at 600 degrees C. The film re-crystallization into the cubic oxynitride phase is observed at 800 degrees C. EDX results confirms that the incorporation of nitrogen into the amorphous films takes place before thermally activated growth of the oxynitride phase and demonstrates that the relative O:N composition in the crystalline phase is dependent on the temperature of the thermal treatment.

3102. 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.

3103. 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.

3104. Complex Compounds of Some 3d Ions with 2 Deoxy D Glucose 1. Iron Complex

Authors: Covaliu, CI; Jitaru, I; Diamandescu, L; Cristea, C

Published: NOV 2009, REVISTA DE CHIMIE, 60, 1145, DOI:

A paramagnetic Fe(III)- 2 deoxy D glucose (Fe-dGl) complex compound with Na(2)[Fe(2)(mu OH)(2)(2dGlc)(2))(2) (H(2)O)(2)Cl(2)] formula was synthesized and characterized by elemental analysis, IR and UV-VIS spectroscopy, thermal analysis TG-DSC, molar electrical conductivity as well as magnetic measurements and Mossbauer spectroscopy, with the aim of developing a new possible MRI contrast agent. The stability in physiological conditions and toxicity of the complex have also been established.

3105. Influence of dye concentration on optical properties of rhodamine 6G doped KAP crystals

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

Published: NOV 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1212, DOI:

Crystals of potassium acid phthalate (KAP) doped with rhodamine 6G (Rh 6G) were grown by slow evaporation method from aqueous solutions. Crystals of good optical quality suitable for optical applications were obtained. Different concentrations of rhodamine 6G (10(-5) M, 2x10(-5) M, 5x10(-5) M and 10(-4) M in the growth solutions) were used in order to tune the optical properties of the crystals. Depending of the dye concentration, the absorption spectra of the dye-doped crystals show several bands in the range between 360 nm and 526 nm. The photoluminescence of the KAP crystals induced by the dye-doping reveals two emission bands peaking at 540 nm and 560 nm.

3106. YBa2Cu3O7-x Thin Films by Citrate-Based Non-fluorine Precursor

Authors: Cui, W; Mikheenko, P; Yu, LM; Button, TW; Abell, JS; Crisan, A

Published: NOV 2009, JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 22, 815, DOI: 10.1007/s10948-009-0504-7

A new fluorine-free chemical solution deposition route has been developed for YBa2Cu3O7-x (YBCO) thin films. The precursor was formed by dissolving metal nitrates and citric acid in ethylene glycol. Polyethyleneimine was used to modify the solution. The preparation of YBCO thin films consisted of repeated dip coating, drying, heat-treating in air and annealing in flowing argon with a small addition of oxygen and with final treatment in pure oxygen. The films were characterized by XRD and SEM and show dominating and well-textured YBCO phase. The AC susceptibility and magnetization measurements reveal a critical temperature about 90 K and a high critical current density, comparable with that of pulse laser deposited films. The simplicity and high performance of the method may be attractive for large-scale superconducting applications.

3107. High-temperature operation of a diode-pumped passively Q-switched Nd:YAG/Cr4+:YAG laser

Authors: Dascalu, T; Pavel, N

Published: NOV 2009, LASER PHYSICS, 19, 2095, DOI: 10.1134/S1054660X0921004X

The output performances of a diode-pumped Nd:YAG laser passively Q-switched by Cr4+:YAG saturable absorber crystal were investigated function of temperature. Increase of the temperature from 25 to 150A degrees C increased slightly the laser pulse energy, and did not change the pulse duration. Furthermore, an increased absorbed energy of the pump radiation was necessary at temperatures higher than 25A degrees C in order to maintain Q-switch operation. Measurements concluded that Cr4+:YAG transmission did not vary when temperature increased to 150A degrees C. The decrease of Nd:YAG emission cross section with temperature and the changes of resonator configuration due to thermal effects were considered as main reasons for this behavior. The results of this work are valuable for designing a laser-ignition system for industrial gas engine or automotive industry.

3108. Evaluation of the shielding effectiveness of a multimode metallic cavity

Authors: Cazanaru, D; Szilagyi, A; Ioachim, A

Published: NOV 2009, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 3, 1242, DOI:

Electronic equipment ran be effectively shielded by the use of a conductive barrier placed between the source of electromagnetic waves and the equipment to be shielded. This paper describes a work which covers some considerations on the materials used for shielding and aspects of the design optimization from the electromagnetic compatibility point of view of a shield with application to a shielding box for a portable computer.

3109. Theoretical investigation of modulated currents in open nanostructures

Authors: Moldoveanu, V; Manolescu, A; Gudmundsson, V

Published: NOV 2009, PHYSICAL REVIEW B, 80, DOI: 10.1103/PhysRevB.80.205325

We investigate theoretically the transport properties of a mesoscopic system driven by a sequence of rectangular pulses applied at the contact to the input (left) lead. The characteristics of the current which would be measured in the output (right) lead are discussed in relation with the spectral properties of the sample. The time-dependent currents are calculated via a generalized non-Markovian master equation scheme. We study the transient response of a quantum dot and of a narrow quantum wire. We show that the output response depends not only on the lead-sample coupling and on the length of the pulse but also on the states that propagate the input signal. We find that by increasing the bias window the new states available for transport induce additional structure in the relaxation current due to different dynamical tunneling processes. The delay of the output signal with respect to the input current in the case of the narrow quantum wire is associated to the transient time through the wire.

3110. 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.