National Institute Of Materials Physics - Romania

Publications

873 articles found

651. Analyzing the measured phase in the multichannel Aharonov-Bohm interferometer

Authors: Tolea, M; Nita, M; Aldea, A

Published: JUL 2010, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 42, 2236, DOI: 10.1016/j.physe.2010.04.022

We address the quantum dot phase measurement problem in an open Aharonov-Bohm interferometer, assuming multiple transport channels. In such a case, the quantum dot is characterized by more than one intrinsic phase for the electrons transmission. It is shown that the phase which would be extracted by the usual experimental method (i.e. by monitoring the shift of the Aharonov-Bohm oscillations, as in Schuster et al., Nature 385 (1997) 417) does not coincide with any of the dot intrinsic phases, but is a combination of them. The formula of the measured phase is given. The particular case of a quantum dot containing a S = 1/2 spin is discussed and variations of the measured phase with

652. Biomolecular urease thin films grown by laser techniques for blood diagnostic applications

Authors: Gyorgy, E; Sima, F; Mihailescu, IN; Smausz, T; Hopp, B; Predoi, D; Sima, LE; Petrescu, SM

Published: MAY 10 2010, MATERIALS SCIENCE & ENGINEERING C-MATERIALS FOR BIOLOGICAL APPLICATIONS, 30, 541, DOI: 10.1016/j.msec.2010.02.003

Matrix assisted pulsed laser evaporation (MAPLE) was used for growing urease thin films designed for biosensor applications in clinical diagnostics. The targets exposed to laser radiation were made from a frozen composite manufactured by dissolving biomaterials in distilled water. We used a UV KrF* (lambda = 248 nm, tau(FWHM) congruent to 30 ns, nu = 10 Hz) excimer source for multipulse laser irradiation of the frozen targets cooled with Peltier elements. The laser source was operated at an incident fluence of 0.4 J/cm(2). Urease activity and kinetics were assayed by the Worthington method that monitors urea hydrolysis by coupling ammonia production to a glutamate dehydrogenase reaction. A decrease in absorbance was measured at 340 nm and correlated with the enzymatic activity of urease. We show that the urease films obtained by MAPLE techniques remain active up to three months after deposition. (C) 2010 Elsevier B.V. All rights reserved.

653. The study of the silicon oxide thickness on crystalline Si by X-ray photoelectron spectroscopy and spectroscopic ellipsometry

Authors: Cotirlan, C; Galca, AC; Ciobanu, CS; Logofatu, C

Published: MAY 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 1097, DOI:

The to study of the total oxide (SiO2+SiOx) thickness, SiO2 and SiOx (e.g. Si2O, SiO, Si2O3) thicknesses on Si(100) crystalline substrate with take-off angles ranging from 30 degrees to 80 degrees has been carried out by spectrometric method. The d(s) X-ray Photoelectron Spectroscopy (XPS) thicknesses were compared with d(EL) thicknesses obtained by fitting the Spectroscopic Ellipsometry (SE) spectra. A qualitatively good correlation is revealed. However, from these estimations of film thicknesses it results that ellipsometry analysis cannot be as accurate as in XPS evaluation. This is due to uncertainty of used optical constants as well due to very thin oxide films used in this work.

654. Multisegment CdTe nanowire homojunction photodiode

Authors: Matei, E; Ion, L; Antohe, S; Neumann, R; Enculescu, I

Published: MAR 12 2010, NANOTECHNOLOGY, 21, DOI: 10.1088/0957-4484/21/10/105202

Electrochemical deposition in nanoporous ion track membranes is used for the preparation of multisegment CdTe-homojunction diode nanowires. Our study is based on the fact that the deposition overpotential strongly influences the composition of the compound semiconductor nanowires. Therefore, the transport behavior of the nanowire devices can be tailored by appropriately choosing a certain sequence of electrodeposition potentials. The wires were characterized using scanning electron microscopy, energy dispersive x-ray analysis, optical spectroscopy and x-ray diffraction. The current-voltage characteristics measured prove that, by appropriately choosing the voltage pulse pattern, one can fabricate nanowires with ohmic or rectifying behavior. The semiconducting nanowires are sensitive to light, their spectral sensitivity being characteristic of CdTe. The preparation of functional nanostructures in such a simple approach provides, as a major advantage, an increase in the process reproducibility and opens a wide field of potential optoelectronic applications.

655. MAPLE deposited thin monomer films of maleimidic derivatives for photonics

Authors: Stanculescu, A; Albu, AM; Socol, G; Stanculescu, F; Socol, M; Preda, N; Rasoga, O; Girtan, M; Iulian, I

Published: MAR 2010, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 12, 739, DOI:

This paper presents a study of some thin monomer films deposited by MAPLE. These monomers have been synthesised from maleic anhydride and aniline derivatives and are characterized by a molecular structure adequate for the generation of optical non-linear phenomena. UV-VIS, FTIR, Raman and Photoluminescence spectroscopy have been used to investigate the influence of the experimental conditions on the properties of the films. X-Ray Diffraction has evidenced a certain degree of disorder in the thin films, which is correlated with the randomly orientated molecules and AFM images have revealed different roughness for different monomer layers and different substrates. Second harmonic measurements have shown a strong signal emitted by the thin film prepared from the monomer with one [-NH-NH-] donor and two [-NO(2)] acceptor groups. This thin film is characterized by good transparency and low photoluminescence emission at excitation with the wavelength of the second harmonic (lambda-400 nm).

656. Structure and properties of silver doped SnSe2 and Ge2Sb2Te5 thin films prepared by pulsed laser deposition

Authors: Popescu, M; Velea, A; Sava, F; Lorinczi, A; Tomescu, A; Simion, C; Matei, E; Socol, G; Mihailescu, IN; Andonie, A; Stamatin, I

Published: MAR 2010, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 207, 520, DOI: 10.1002/pssa.200982900

Amorphous thin films of SnSe2 and Ge2Sb2Te5 doped by different amount of silver (0.1, 0.2, 0.5 and 1 Ag atoms per formula unit) have been prepared by pulsed laser deposition (PLD) starting from solid polycrystalline targets. The films were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and atomic force microscopy (AFM). The good gas sensing properties for CO, as well as the sensitivity for CH4 and NO of the Ag; doped SnSe2 films have been demonstrated in the composition SnSe2Ag0.2. The structural effect of silver introduced in Ge2Sb2Te5 matrix has been investigated. The freshly deposited thin films doped by various amount of Ag develop three phases: an amorphous one, and two crystalline phases consisting of a major fcc cubic phase of AgSbTe2 and a minor cubic phase of composition Ag2Te. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

657. Structural refinements and ab-initio calculations for Au3Zr phase

Authors: Palade, P; Ciobanu, C

Published: FEB 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 168, DOI:

Au3Zr intermetallic phase was obtained as pure phase by melt spinning technique. The sample with the same composition obtained by powder metallurgy exhibits some Au4Zr impurity. Rietveld refinements of the X-Ray data were done to obtain the unit cell parameters and atom positions inside the unit cell. Geometry optimizations for the atom positions inside the unit cell were performed by using ab-initio band structure calculations. The calculated values agree well with the ones obtained by Rietveld refinements of the diffraction data. The electronic mechanisms are explained on the basis of the projected densities of states to atom sites.

658. Films and crystalline powder of BiI3 intercalated with ammonia

Authors: Preda, N; Mihut, L; Baibarac, M; Baltog, I; Pandele, J; Andronescu, C; Fruth, V

Published: JAN 2010, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 30, 479, DOI: 10.1016/j.jeurceramsoc.2009.05.046

Intercalation, i.e. the insertion of guest species in a crystalline layered structure, is an efficient route for generating new materials with novel properties. Thin films and crystalline powder of BiI3 layered semiconductor were intercalated by exposure to ammonia vapors at room temperature. The intercalated compound was studied by thermo-gravimetric analysis, differential scanning calorimetry, X-ray diffraction, UV-vis optical absorption, FTIR spectroscopy and Raman scattering. After exposure of BiI3 to ammonia the formation of a new phase, BiI3(NH3)(3.83), was evidenced by thermal analysis. The intercalation process leads to a blue shift of the BiI3 Optical absorption edge by 0.5 eV. The appearance of new Raman lines at 135 and 353 cm(-1) in the Raman spectrum of intercalated BiI3 is considered as an evidence of the chemical interaction between the ammonia molecules and BiI3 lattice. (C) 2009 Elsevier Ltd. All rights reserved.

659. Synthesis and ultrasonic characterization of hydroxyapatite ceramic powders

Authors: Predoi, D; Derible, S; Duflo, H

Published: JAN 2010, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 4, 114, DOI:

Calcium phosphate compounds have been studied for biomedical applications due to chemical and structural similarity to the mineral phase of bone and tooth. The composition, physico-chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparative conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapatite (HAp) powders. The present paper refers to calcinations of hydroxyapatite ceramics at 600, 800 and 1000 degrees C. The effect of heat treatment was previously investigated by X-ray diffraction (XRD). The ultrasonic characterisation of hydroxyapatite powders were performed using the ultrasonic air-coupling technique. Modulated ultrasonic signals of 450 kHz central frequency have been transmitted through the hydroxyapatite ceramics specimens. Correlation between signals allowed to draw some conclusions concerning density, attenuation and influence of the preparation temperature influence on these samples. These comparisons and correlation of methods, allow a better characterization of such important materials.

660. THE INFLUENCE OF SYNTHESIS PARAMETERS ON SIZE AND MORPHOLOGY OF POLY(STYRENE-HYDROXYETHYL METHACRYLATE) COLLOIDS

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

Published: OCT-DEC 2010, DIGEST JOURNAL OF NANOMATERIALS AND BIOSTRUCTURES, 5, 1065, DOI:

Poly(styrene-hydroxyethyl methacrylate) [P(ST-HEMA)] latex particles were prepared by surfactant-free emulsion copolymerization. As water-soluble initiator was used potassium persulfate (KPS). The influence of different reactions parameters, such as the reaction temperature, the both monomers (ST and HEMA) concentrations and the KPS concentration on the particles average diameter and particles size dispersion was investigated. Generally monodisperse spherical particles are synthesized, but we also obtained stable large three-dimensional colloidal aggregates. These are formed by the agglomeration of monodispersed spheres in certain polymerization conditions. The P(ST-HEMA) monodispersed spheres with 350 nm average diameter were assembled into colloidal crystals using dip-coating technique. Colloidal crystals with different thickness were obtained by modifying two experimental factors, the colloidal concentration and the substrate lifting speed. The morphologies of copolymer latex particles and colloidal crystals were observed using scanning electron microscopy (SEM). The optical properties of colloidal crystals films were also investigated by transmission spectroscopy.