National Institute Of Materials Physics - Romania

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886 articles found

731. Nanocrystalline Er : YAG thin films prepared by pulsed laser deposition: An electron microscopy study

Authors: Stanoi, D; Popescu, A; Ghica, C; Socol, G; Axente, E; Ristoscu, C; Mihailescu, IN; Stefan, A; Georgescu, S

Published: JUL 31 2007, APPLIED SURFACE SCIENCE, 253, 8272, DOI: 10.1016/j.apsusc.2007.02.113

We report the synthesis of well crystallized stoichiometric Er:YAG thin films by pulsed laser deposition from Er:YAG targets in low pressure oxygen, followed by a post-deposition treatment at 1400 degrees C in environmental air for 19 h. The structure and morphology of the films were examined by transmission electron microscopy and selected area electron diffraction. We demonstrated that the subsequent application of pulsed laser deposition and heat treatment resulted in the formation of well crystallized single phase cubic Er:YAG nanostructured coatings. (c) 2007 Elsevier B.V. All rights reserved.

732. Structure, properties and gas sensing effect of SnSe2 films prepared by pulsed laser deposition method

Authors: Popescu, M; Sava, F; Lorinczi, A; Socol, G; Mihailescu, IN; Tomescu, A; Simion, C

Published: JUN 15 2007, JOURNAL OF NON-CRYSTALLINE SOLIDS, 353, 1869, DOI: 10.1016/j.jnoncrysol.2007.02.055

Amorphous SnSe, films were prepared by pulsed laser deposition (PLD) from solid polycrystalline targets. The atomic scale structure has been revealed by X-ray diffraction. Hardness and electrical properties were measured. Strong gas sensing properties have been evidenced for the first time in heat treated films. (c) 2007 Elsevier B.V. All rights reserved.

733. Conduction mechanism involved in sensing mechanism of SnSe2

Authors: Tomescu, A; Simion, CE

Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1897, DOI:

Simple investigation of the electrical resistance does not permit to draw up the conduction mechanism of thin SnSe2 layers. The presence of reducing gas atmospheres, respectively CH4, CO and H2O could change the concentration of the free charge carriers, beside electron affinity changes induced by the appearance of surface dipoles. Work function and electrical resistance were simultaneous investigated for thin SnSe2 films. The experimental results permit the evaluation of electron affinity and band-bending behavior. Conduction mechanism can be discussed in terms of surface or bulk contribution.

734. Varieties of nanostructured carbon grown by expanding radiofrequency plasma beam

Authors: Vizireanu, S; Mitu, B; Dinescu, G; Nistor, L; Ghica, C; Maraloiu, A; Stancu, M; Ruxandra, G

Published: JUN 2007, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 9, 1652, DOI:

Results regarding the growth of carbon nanostructures by using a low-pressure expanding radiofrequency plasma jet are reported. The growth was performed in an argon plasma injected with acetylene precursor, in the presence of ammonia or hydrogen, on a substrate covered with nickel or cobalt catalysts. Various forms of nanostructured carbon material were obtained, depending on the catalyst size, ammonia or hydrogen / acetylene ratio and substrate temperature. The results exemplified in the paper describe nickel nanoparticles coated in highly ordered graphite shells, granular carbon, two dimensional carbon nanoflakes, nanowires and nanorods.

735. 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.

736. 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.

737. 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.

738. 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.

739. 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.

740. 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.