National Institute Of Materials Physics - Romania

Publications

5714 articles found

2601. Carbon layers cleaning from inside of narrow gaps by a RF glow discharge

Authors: Stancu, C; Teodorescu, M; Galca, AC; Dinescu, G

Published: JUL 25 2011, SURFACE & COATINGS TECHNOLOGY, 205, S438, DOI: 10.1016/j.surfcoat.2011.03.090

The paper focuses on the utilization of radiofrequency discharges at intermediate pressures for plasma removal of carbon residuals or layers from narrow gaps and channels. It is shown that by proper handling of the discharge power and pressure it is possible to control the development of plasma inside narrow gaps, in the proximity of surfaces to be cleaned. The discharge operation inside gaps having the width in the range 0.6-2 mm was demonstrated. The cleaning effectiveness is exemplified for castellated surfaces having rectangular gaps coated with hydrogenated amorphous carbon layers. Cleaning of large surfaces can be approached with a movable "plasma shower" type device. (C) 2011 Elsevier B.V. All rights reserved.

2602. (Ti,Cr,Nb)CN coatings deposited on nitrided high-speed steel by cathodic arc method

Authors: Braic, M; Braic, V; Balaceanu, M; Vladescu, A; Zoita, CN; Lungu, CP; Grigorescu, CEA; Grigore, E; Logoftu, C

Published: JUL 25 2011, SURFACE & COATINGS TECHNOLOGY, 205, S213, DOI: 10.1016/j.surfcoat.2011.03.030

The combined processes of plasma nitriding and cathodic arc deposition of (Ti,Cr,Nb)CN coatings were applied to HSS substrates. The nitrided layers, obtained in a mixture of H-2 (70%) and N-2 (30%) at two different temperatures (480 degrees C and 510 degrees C), were examined for the microhardness depth profiles. Characterization of the duplex coatings was performed by investigating elemental and phase composition, texture, hardness, friction and wear. XRD and XPS analyses revealed the formation of a mixture of a carbonitride fcc solid solution, in a dominant proportion, and metallic chromium. The film hardness was measured to be similar to 34 GPa. The duplex (Ti,Cr,Nb)CN coatings exhibited superior tribological behavior as compared to both nitrided layers and non-duplex coatings. (C) 2011 Elsevier B.V. All rights reserved.

2603. New structural features of non-crystalline tetrahedrally bonded networks A modeling approach

Authors: Sava, F; Popescu, M

Published: JUL 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 2554, DOI: 10.1016/j.jnoncrysol.2011.02.056

A large model of amorphous silicon (2052 atoms) with 0.5% dangling bonds has been built and investigated. The refinement of the coordinates evidenced the presence of small domains with advanced ordering. These domains preclude the formation of crystallization nuclei and play an essential role in the redistribution of the defects in the material with homogenization of the free energy and stabilization against aging. An effect of amorphization of the ordered nuclei due to free energy redistribution is assessed. The glass relaxation of a-Si (a-Ge) occurring during heating below T(g) receives a natural explanation as a structural change from local quasi-ordering to homogeneous disordering. (C) 2011 Elsevier B.V. All rights reserved.

2604. New insight into phase change memories

Authors: Velea, A

Published: JUL 1 2011, JOURNAL OF NON-CRYSTALLINE SOLIDS, 357, 2631, DOI: 10.1016/j.jnoncrysol.2011.02.014

The switching mechanism in phase change memories was described on the basis of minimum switching unit: the commuton. A commuton is a minimum cluster of atoms that supports a reversible phase change from high to low electrical conduction state and back under the influence of an external signal. The switching process in a phase change chalcogenide film was modeled using two dimensional cellular automata approach. A system of 50 x 50 cells, each cell containing a commuton, was simulated. In the particular case of Ge(2)Sb(2)Te(5) (investigated here) this system corresponds to a 30 x 30 nm area. The formation of the percolation path as a function of phase change induced in commutons explains the switching phenomenon. The influence of the percent of defects in the material on the percolation threshold has been studied. (C) 2011 Elsevier B.V. All rights reserved.

2605. Angle-resolved evanescent-wave cavity ring-down spectroscopy for thin film-solid interface characterization

Authors: Cotirlan, C; Logofatu, C; Rizea, A; Lazarescu, MF

Published: JUL 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 714, DOI:

A new method, that involves Evanescent-Wave Cavity Ring-Down Spectroscopy (EW-CRDS), is presented. This method is useful for the study of thin films on optical solid surfaces. The new design of experimental set-up incorporates a semicylindrical prism with a plane surface where the Total Internal Reflection (TIR) effect appears. The antireflex (AR) coated cylindrical surface of the prism induces the stability of resonant cavity. The evanescent wave generated at the plane surface of the prism probes the absorption by matter in the vicinity of the prism. A general discussion of design criteria is presented to quantify intrinsic losses, and then absorption spectra for Rhodamine chloride R590 from 555 to 560 nm are presented to demonstrate the sensitivity of the system. The layer of R590 on BK7 surfaces is deposited from a solution of R590 in ethanol (92% purity) with 51 mg/l concentration. After vaporization of the ethanol the dye layer on surfaces is supposed to be uniform. This implementation of TIR surface in a resonant cavity provides a powerful new spectroscopic tool especially to angle-resolved diagnostic for interfaces and thin-films. The loss spectrum can be obtained for an angular range from the TIR critical angle to a maximum angle when the resonance of system is lost.

2606. Transient thermal effects in solid noble gases as materials for the detection of Dark Matter

Authors: Lazanu, I; Lazanu, S

Published: JUL 2011, JOURNAL OF COSMOLOGY AND ASTROPARTICLE PHYSICS, DOI: 10.1088/1475-7516/2011/07/013

Noble solid gases are promising detector materials to be used in the search for dark matter. In the present paper a systematic analysis of the transient phenomena associated with the stopping of recoils in noble gases in the solid phase is performed for the first time. The investigated energy range of the recoils corresponds to the elastic scattering of WIMPs from the galactic halo in these materials. A thermal spike model, previously developed by the authors, is extended and applied to solid noble gases. Ionization, scintillation and nuclear. energy loss processes are considered and included in the model, as well as the coupling between the subsystems. The development of the temperature pulse in space and time in solid Ar, Kr and Xe is analysed for different energies of the WIMP, and for different initial temperatures of the material. Phase transitions are possible in particular cases. The results of the model could be used as supplementary information in respect to ionization and scintillation, for detection and particle identification.

2607. BET and XRD studies on the hydroxyapatite and europium doped hydroxyapatite

Authors: Ciobanu, CS; Andronescu, E; Predoi, D

Published: JUL 2011, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 13, 824, DOI:

Europium doped hydroxyapatite (Eu:HAp) nanocristalline powders was synthesized by co-precipitation method by setting the atomic ratio of Eu/[Eu + Ca] at 0% and 2% and [Ca+Eu] /P at 1.67. The structural properties were characterized by X-ray diffraction (XRD). Nitrogen adsorption-desorption isotherms were obtained on different samples using BET method. The X-ray diffraction analysis revealed that hydroxyapatite is the unique crystalline constituent of all the samples, indicating that Eu has been successfully inserted into the HAp lattice. Based on N-2 adsorption-desorption isotherms investigation, the pore size, surface area and pore volume of europium doped hydroxyapatite are 16.57 nm, 115.06 m(2)/g and 0.48 cm(3)/g.

2608. Synthesis and characterization of indium oxide-hematite magnetic ceramic solid solution

Authors: Sorescu, M; Xu, TH; Diamandescu, L; Hileman, D

Published: JUL 2011, HYPERFINE INTERACTIONS, 199, 386, DOI: 10.1007/s10751-011-0267-y

Indium oxide-doped hematite xIn(2)O(3*) (1 - x) alpha-Fe2O3 (molar concentration x = 0.1-0.7) solid solutions were synthesized using mechanochemical activation by ball milling. XRD patterns yield the dependence of lattice parameters and grain size as function of milling time. After 12 h of milling, the completion of In3+ substitution of Fe3+ in hematite lattice occurs for x = 0.1. For x = 0.3, 0.5 and 0.7, the substitutions between In3+ and Fe3+ into hematite and respectively, In2O3 lattices occur simultaneously. The lattice parameters of alpha-Fe2O3 (a and c) and In2O3 (a) vary with milling time. For x = 0.1, Mossbauer spectra were fitted with one, two, or three sextets versus milling time, corresponding to gradual substitution of In3+ for Fe3+ in hematite lattice. For x = 0.3, Mossbauer spectra after milling were fitted with three sextets and two quadrupole-split doublets, representing In3+ substitution of Fe3+ in hematite lattice and Fe3+ substitution of In3+ in two different sites of In2O3 lattice. For x = 0.5 and 0.7, Mossbauer spectra fitting required two sextets and one quadrupole-split doublet, representing coexistence of In3+ substitution of Fe3+ in hematite lattice and Fe3+ substitution of In3+ in indium oxide lattice. The recoilless fraction studied versus milling time for each molar concentration exhibited low values, consistent with the occurrence of nanoparticles in the system. SEM/EDS measurements revealed that the mechanochemical activation by ball milling produced xIn(2)O(3*)(1 - x)alpha-Fe2O3 solid solution system with a wide range of particle size distribution, from nanometer to micrometer, but with a uniform distribution of Fe, In, and O elements.

2609. Structural and electrical properties of yttrium-doped ceria ceramic composites

Authors: Ionascu, AM; Mercioniu, I; Notingher, PV; Popescu-Pogrion, N

Published: JUL 2011, OPTOELECTRONICS AND ADVANCED MATERIALS-RAPID COMMUNICATIONS, 5, 777, DOI:

The attractive properties of Yttria doped ceria, particularly the structural and material properties, have led to vast research efforts to investigate and develop such materials. One of the main applications of this ceramic is in the IT-SOFC. The aim of this paper is the preparation and characterization of Y doped Ceria and low doped alpha-Al2O3, a new composite for IT-SOFC (10 mol %) Y:CeO2 and (150 ppm) Y:alpha-Al2O3 composite were obtained by sol-gel or mechanical route for 10YDC and 150 Y:alpha-Al2O3. Shapes, size distributions and the mean of grains were determined by SEM, EDX and statistical investigations.

2610. The pinning force density in polycrystalline Bi1.8Pb0.4Sr2Ca2-xYxCu3Oy multiphase systems

Authors: Mihalache, V; Deac, IG; Pop, AV; Miu, L

Published: JUL 2011, CURRENT APPLIED PHYSICS, 11, 1014, DOI: 10.1016/j.cap.2011.01.015

ac susceptibility measurements as a function of temperature T and the ac magnetic field amplitude, Hac, have been performed on five superconducting Bi1.8Pb0.4Sr2Ca2-xYxCu3Ox polycrystalline samples (x = 0, 0.005, 0.04, 0.15 and 0.36, and with the volume fraction of the Bi2Sr2Ca2Cu3Oy (2223) phase, f approximate to 100%, 100%, 64%, 0% and 0%, respectively. By using the Muller model for granular superconductors, we found that the pinning force density obtained from the imaginary peak of chi ''(T) is strongly dependent on the doping level. To describe this dependence we adopted the multilayer model (a stack of superconducting, S, and normal, N, layers) of a superconductor. In the framework of this model, we demonstrated that (a) the yttrium addition influences the degree of coupling between the adjacent S layers (and thereby, the pinning strength) through the modification of the carrier concentration and of the effective thickness of the N layers, and (b) the intergrowth of Bi2Sr2CaCu2O delta (2212) layers within the 2223 grains has an important influence on the thickness of N. (C) 2011 Elsevier B.V. All rights reserved.