National Institute Of Materials Physics - Romania

Publications

5781 articles found

3391. Irradiation defects in superhard cubic boron nitride single crystals

Authors: Nistor, SV; Ghica, D; Stefan, M; Nistor, LC; Goovaerts, E; Taniguchi, T

Published: JUN 2008, NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS, 266, 2787, DOI: 10.1016/j.nimb.2008.03.117

Single crystallites of superhard, semiconducting, n-type, amber colored and p-type, blue colored, Be-doped cubic boron nitride have been irradiated either with UV (350 nm) light or with an intense beam of accelerated (1 MeV) electrons. The examination of the irradiated samples at low temperatures by high frequency W (95 GHz)-band electron spin resonance reveals several new, radiation-induced, isotropic paramagnetic centers. The UV irradiation of both types of crystals yields centers involving very likely protons. In the amber c-BN crystals the irradiation with I MeV electrons results in the formation of vacancy associated paramagnetic defects and quasi-free electrons in colloidal particles. (C) 2008 Elsevier B.V. All rights reserved.

3392. Study of osteoblast interaction with iron oxide nanoparticles coated with dextrin in cell culture

Authors: Vatasescu-Balcan, RA; Predoi, D; Costache, M

Published: JUN 2008, FEBS JOURNAL, 275, 374, DOI:

3393. ARXPS analysis of silicon oxide films

Authors: Negrila, CC; Cotirlan, C; Ungureanu, F; Logofatu, C; Lazarescu, RVGMF

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1383, DOI:

Angle-resolved X-ray Photoelectron Spectroscopy (ARXPS) has been performed on (100) Si surfaces in different conditions as regards the oxides nature - native oxides, thermally formed oxides, and also after a cleaning procedure by Ar+ ion sputtering (e.g. E= 2 keV). The most sensitive angle to surface oxidation states (Si1+, Si2+, Si3+, Si4+) was the take-off-angle (TOA): 25 degrees. Native oxides and thermally oxide phases on Si surfaces consists in a mixture of Si2O, SiO, Si2O3 and SiO2. The XPS measurements have putted into evidence a higher concentration of suboxides in high oxidation state (Si3+) on naturally oxidized Si substrates. The thermally oxidized Silicon surfaces contain suboxides in a low oxidation state (Si1+). The Ar+ ion sputtering removed rapidly the superficial silicon oxides. The analysis and computation of SiO2 film thickness on crystalline Silicon was done in the frame of modified Bethe equation for Electron inelastic mean free path (IMFP) and taking into account the intensity of SiO2 peak and Si peak together with the TOA in the XPS measurement. Native oxide thickness for SiO2 was d(oxy) similar to 24 angstrom and for thermally oxidized sample was d(oxy) similar to 27 angstrom. Due to the slightly difference in the nature oxidation states it is suggested that the silicon dioxide appeared from two different kinetics in the oxidation processes.

3394. Microstructural and magnetic characterization of CuNb/Nb3Sn wires with different architectures

Authors: Sandim, MJR; Cangani, MP; Sandim, HRZ; Ghivelder, L; Awaji, S; Badica, P; Watanabe, K

Published: JUN 2008, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 18, 1025, DOI: 10.1109/TASC.2008.920575

In this work we focus on the microstructural and magnetic characterization of CuNb/Nb3Sn wires with different architectures (design and reinforcement). The microstructural characterization was performed using scanning electron microscopy. AC magnetic susceptibility was measured with field applied both parallel and perpendicular to the wire axis. The heat treatment performed to form the A-15 superconducting phase leads to partial spheroidization followed by coarsening of the Nb filaments in the reinforcement material. The differences concerning the microstructure of the reinforcement material among the investigated wires were reflected in the broadening of the superconducting transition of Nb, more evident for a field applied parallel to the wire axis. From the magnetic data the wires were also compared in terms of the superconducting volume fraction.

3395. Influence of deviatoric strain for superconducting parameters of Nb3Sn wires

Authors: Oguro, H; Awaji, S; Nishijima, G; Badica, P; Shikanai, F; Kamiyama, T; Katagiri, K; Watanabe, K

Published: JUN 2008, IEEE TRANSACTIONS ON APPLIED SUPERCONDUCTIVITY, 18, 1050, DOI: 10.1109/TASC.2008.921907

The tensile strain dependence of the upper critical field B-c2 for Nb3Sn wires was measured using a new apparatus for applying tension at low temperature. The critical current I-c calculated from the strain-dependent B-c2 measurements is the almost consistent with the measured I-c. In the measurements by a new apparatus, the axial and the lateral applied strains were examined by the strain gauges attached onto the wire. The deviatoric strain epsilon(dev) and the hydrostatic strain epsilon(hyd) were estimated by the axial and the lateral strain. We found the deviatoric strain dependence of B-c2 is different between the tensile and compressive strain states. This means that the hydrostatic strain also should be taken into account in order to understand the strain effects on the superconducting properties of Nb3Sn.

3396. The characterization of surfaces of electro polished 316L stainless steel for orthopedic implant applications

Authors: Samide, A; Bibicu, I; Oprea, B; Cioatera, N; Ciuciu, A

Published: JUN 2008, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 10, 1436, DOI:

The characterization of the surface of electro polished 316L stainless steel by using poly(O-2-hydroxyethyl) starch (PETA) in physiological serum (PS) is discussed according to electrochemical measurements, scanning electron microscopy and Mossbauer Spectroscopy. The results obtained through polarization curves indicate that critical potential in pitting (E-cp) are shifted to a higher values with the increase in PETA concentration; PETA reduces anodic dissolution and also decrease of the corrosion current (i(corr)). Decrease of the corrosion current (i(corr)) was associated with a shift of corrosion potential (E-corr) to a less negative values. The polarization resistance(R-p) increases for the surfaces which were electro polished in physiological serum in the presence of PETA. Scanning electron microscopy(SEM) shown no evidence of corrosion pits on Surfaces of Electro polished 316L Stainless Steel, but the formation of a thick film on the steel surface was observed. The surface Mossbauer spectrometry proves the uniformity, compactness and stability of the passive films.

3397. Doped sol-gel TiO2 films for biological applications

Authors: Gartner, M; Trapalis, C; Todorova, N; Giannakopoulou, T; Dobrescu, G; Anastasescu, M; Osiceanu, P; Ghita, A; Enache, M; Dumitru, L; Stoica, T; Zaharescu, M; Bae, JY; Suh, SH

Published: MAY 20 2008, BULLETIN OF THE KOREAN CHEMICAL SOCIETY, 29, 1042, DOI:

Mono and multilayer TiO2(Fe, PEG(600)) films were deposited by the dip-coating on SiO2/glass substrate using sol-gel method. In an attempt to improve the antibacterial properties of doped TiO2 films, the influence of the iron oxides and polyethilenglycol (PEG(600)) on the morphological, optical, surface chemical composition and biological properties of nanostructured layers was studied. Complementary measurements were performed including Spectroscopic Ellipsometry (SE), Scanning Electron Microscopy (SEM) coupled with the fractal analysis, X-Ray Photoelectron Spectroscopy (XPS) and antibacterial tests. It was found that different concentrations of Fe and PEG(600) added to coating solution strongly influence the porosity and morphology at nanometric scale related to fractal behaviour and the elemental and chemical states of the surfaces as well. The thermal treatment under oxidative atmosphere leads to films densification and oxides phase stabilization. The antibacterial activity of coatings against Escherichia Coli bacteria was examined by specific antibacterial tests.

3398. Characteristics of arc plasma deposited TiAlZrCN coatings

Authors: Balaceanu, M; Braic, V; Kiss, A; Zoita, CN; Vladescu, A; Braic, M; Tudor, I; Popescu, A; Ripeanu, R; Logofatu, C; Negrila, CC

Published: MAY 15 2008, SURFACE & COATINGS TECHNOLOGY, 202, 3987, DOI: 10.1016/j.surfcoat.2008.02.005

TiAlZrCN superhard coatings, in which Ti and Al were additions to ZrCN base compound, were prepared by the cathodic arc method. The films were deposited on Si, plain carbon steel and high-speed steel substrates in a mixture of N-2 and CH4 gases. Elemental and phase composition, chemical bondings, texture, surface roughness, hardness, adhesion, tribological characteristics and erosive-corrosive resistance were investigates as a function of gas composition and total gas flow rate, using XPS, GDOES and XRD techniques, surface profilometry, microhardness and scratch adhesion measurements, tribological and erosive tests. It was shown that the properties and performance of the coatings were strongly dependent on the CH4/(CH4+N-2) flow rate and also on the total gas flow. The tribological and anti-erosive characteristics of the TiAlZrCN coatings were found to be superior to those of reference films (ZrN, ZrC, ZrCN, and TiAlCN). Maximum hardness values (42-45 GPa) were obtained for the films prepared at CH4/(CH4+N2) ratios ranging from 0.2 to 0.4. (c) 2008 Elsevier B.V. All rights reserved.

3399. On Eisenbud's and Wigner's R-matrix: A general approach

Authors: Behrndt, J; Neidhardt, H; Racec, ER; Racec, PN; Wulf, U

Published: MAY 15 2008, JOURNAL OF DIFFERENTIAL EQUATIONS, 244, 2577, DOI: 10.1016/j.jde.2008.02.004

The main objective of this paper is to give a rigorous treatment of Wigner's and Eisenbud's R-matrix method for scattering matrices of scattering systems consisting of two selfadjoint extensions of the same symmetric operator with finite deficiency indices. In the framework of boundary triplets and associated Weyl functions an abstract generalization of the R-matrix method is developed and the results are applied to Schrodinger operators on the real axis. (C) 2008 Elsevier Inc. All rights reserved.

3400. Transport properties of electrodeposited ZnO nanowires

Authors: Tazlaoanu, C; Ion, L; Enculescu, I; Sima, M; Enculescu, M; Matei, E; Neumann, R; Bazavan, R; Bazavan, D; Antohe, S

Published: MAY 2008, PHYSICA E-LOW-DIMENSIONAL SYSTEMS & NANOSTRUCTURES, 40, 2507, DOI: 10.1016/j.physe.2007.07.013

ZnO nanowires were electrodeposited by using a template approach. Ion track polycarbonate foils (30 mu m thick) were used as templates. Current-voltage (I-V) characteristics were recorded in the temperature range 40-300 K. I-V characteristics show a symmetric, non-linear shape, at temperatures greater than 240 K and voltages greater than 15 V. At lower temperatures, linear characteristics were recorded for the voltage range used. The temperature dependence of the electrical resistance is activated, with activation energy of 0.42 eV at temperatures greater than 240 K. (C) 2007 Elsevier B.V. All rights reserved.