National Institute Of Materials Physics - Romania

Publications

847 articles found

691. Preparation of metallic nanowires with magnetic properties using the template method

Authors: Enculescu, I; Sima, M; Enculescu, M; Ghica, C; Enache, M; Neumann, R

Published: MAY 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1470, DOI:

Metallic nanowires with magnetic properties were prepared by electrochemical deposition in nanoporous ion track membranes. Thus, we prepared Co-Cu alloy and Co/Cu multilayered nanowires. The technique allows the preparation of uniform arrays of parallel nanowires with desired properties. The process of electrochemical deposition of metals in nanoporous membranes was studied by means of cyclic voltammetry and impedance spectroscopy. The influences of deposition conditions such as bath composition, temperature and deposition potential on the morphological, structural and compositional properties of the nanowires were systematically studied.

692. Localization and movement of native interstitials in chlorinated SrCl2 : Fe crystals

Authors: Ghica, D; Nistor, SV; Goovaerts, E

Published: MAR 2007, PHYSICA STATUS SOLIDI A-APPLICATIONS AND MATERIALS SCIENCE, 204, 698, DOI: 10.1002/pssa.200673878

The formation of the electron trapped Fe+(IV) centre, produced by X-ray irradiation at 80 K and further annealing at temperatures of up to 700 K in chlorinated SrCl2: Fe crystals, has been investigated by Electron Paramagnetic Resonance. Our studies report the transformation of the monoclinic Fe+(III) centre into the axial Fe+(IV) centre above 450 K. The formation of the Fe+(IV) centre is attributed to the presence and thermally activated movement of neighbouring interstitial chlorine and alkali impurity Ne ions. (c) 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

693. TEM characterization of extended defects induced in Si wafers by H-plasma treatment

Authors: Ghica, C; Nistor, LC; Bender, H; Richard, O; Van Tendeloo, G; Ulyashin, A

Published: JAN 21 2007, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 40, 400, DOI: 10.1088/0022-3727/40/2/016

Silicon hydrogenation is nowadays studied with the aim of developing and improving a technological method known as 'smart cut' used in the fabrication of 'silicon-on-insulator' devices. The goal of our study is to characterize the defects induced in silicon wafers after exposure to hydrogen RF plasma. Si < 001 > wafers have been treated at 250 degrees C under hydrogen RF plasma at 110 MHz, for various durations. The main features observed by transmission electron microscopy (TEM) are surface roughening and the presence of three kinds of defects: {111} planar defects, {100} planar defects and H bubbles. In this work a study using conventional TEM and high resolution transmission electron microscopy (HRTEM) techniques is presented on H bubbles and {100} planar defects induced in Si wafers by H-plasma treatment. The strain field around the defects is qualitatively characterized by diffraction contrast analysis and quantitatively by the geometrical phase method, by processing the HRTEM images.

694. Percolation phenomena in silicon - Based nanocrystalline systems

Authors: Lepadatu, AM; Rusnac, E; Stavarache, I

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, 578, DOI: 10.1109/SMICND.2007.4519789

The present paper analyzes the appearance of voltage percolation thresholds in the current - voltage characteristics measured on silicon-based nanocrystalline systems that present random space distribution of the nanocrystallites. This percolation phenomenon is explained on the basis of the probability of tunneling under applied bias and is related to the samples microstructure.

695. Some contributions to the understanding of the puzzle of physical processes of degradation in irradiated silicon

Authors: Lazanu, S; Lazanu, I; Ciurea, ML

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

In the present paper, we intend to bring some clarifications related to the role played by primary defects in long term degradation, to the dependence of degradation on the orientation of the wafer, as well as on the spatial distribution of the degradation produced by low energy particle irradiation.

696. A. comparative study of micro crystalline and nanocrystalline lead sulfide based PbS/SiO2/Si heterostructures

Authors: Stancu, V; Pentia, E; Goldenblum, A; Buda, M; Iordache, G; Botila, T

Published: 2007, ROMANIAN JOURNAL OF INFORMATION SCIENCE AND TECHNOLOGY, 10, 66, DOI:

The PbS micro-crystalline and nano-crystalline films were obtained using the Chemical Bath Deposition method. We investigated comparatively the structural, electrical and photoconductive properties of these films deposited on glass. PbS/SiO2/Si heterostructures made with nanocrystalline PbS layers present interesting peculiarities. Their C-V curves show hysterezis. In a field effect arrangement it is possible to control the photoconductive short and long wavelength ratio response. The heterostructure properties were explained by taking into account the interface charged traps.

697. Influence of calcination temperature on the electrical signal of SnSe2 sensors

Authors: Tomescu, A; Simion, CE

Published: 2007, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 1, 121, DOI:

d The effect induced by the calcination temperature on gas sensing properties of thin SnSe2 layers exposed to reducing gas species, respectively CH4, CO and H2O, has been investigated. The sensor signal defined as the ratio between the electrical resistance in air and that in the test gas atmosphere has been used as monitoring parameter.

698. Probing cellulose wettability by electron paramagnetic resonance

Authors: Ionita, G; Ghica, C; Ionita, P

Published: 2007, MATERIALS SCIENCE-POLAND, 25, 1017, DOI:

Carboxymethyl-cellu lose has been labelled with a stable free radical by reaction with 4-aminotempo in the presence of a coupling agent (EEDQ). The spin-labelled cellulose is highly stable, no leaking being noticed after months at room temperature. EPR spectroscopy was used as a main tool to study the wettability of such a material. The EPR spectrum of the dry spin-labelled cellulose shows the expected anisotropy, while addition of several solvents (acetone, ethyl acetate, DCM, methanol, toluene, PEG 200) induces the splitting of the spectrum into a two component system. Thus, the EPR spectrum is composed of a mobile component superimposed onto an immobilized one. Addition of water leads to a monocomponent isotropic spectrum. These data clearly indicate the presence of two types of sites to which the spin-label is attached. Variable temperature EPR spectra showed that an increase of temperature results in an increase in the mobility of the spin-label. Deposition of plain or spin-labelled gold nanoparticles on the cellulose fibres also affects the structure of the polymeric chain, as seen by changes in the EPR spectra.

699. Why the energy levels observed in electrical transport, phototransport and photoluminescence are different?

Authors: Ciurea, ML; Iancu, V

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI: 10.1109/SMICND.2007.4519643

The paper presents an analysis of the electrical transport, phototransport and photoluminescence measurements performed on silicon-based nanocrystalline systems. The experimental results are discussed within the frame of a quantum confinement model. It is proved that the differences between the energy levels identified in the measurements are related to the quantum selection rules specific to each process. It is also proved that, at nanometric scale, the nature of the atoms composing the nanocrystal represents a first order correction, while the size represents a zero order factor.

700. Quantum confinement model for phototransport processes in nanocrystalline porous silicon

Authors: Ciurea, ML; Stavarache, I; Iancu, V

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

The paper presents a quantum confinement model which describes the phototransport processes in nanocrystalline porous silicon. The model supposes that the nanocrystallites surface/interface acts as the walls of an infinite rectangular quantum well, introducing discrete confinement energy levels. This model is proved able to also describe the photoluminescence and the temperature dependence of the dark current in the same samples. Its results are in agreement with the Microstructure investigations.