National Institute Of Materials Physics - Romania

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5781 articles found

4221. Hydroxyapatite thin films grown by pulsed laser deposition and radio-frequency magnetron sputtering: comparative study

Authors: Nelea, V; Morosanu, C; Iliescu, M; Mihailescu, IN

Published: APR 30 2004, APPLIED SURFACE SCIENCE, 228, 356, DOI: 10.1016/j.apsusc.2004.01.029

Hydroxyapatite (HA) thin films for applications in the biomedical field were grown by pulsed laser deposition (PLD) and radio-frequency magnetron sputtering (RF-MS) techniques. The depositions were performed from pure hydroxyapatite targets on Ti-5Al-2.5Fe (TiAlFe) alloys substrates. In order to prevent the HA film penetration by Ti atoms or ions diffused from the Ti-based alloy during and after deposition, the substrates were pre-coated with a thin buffer layer of TiN. In both cases, TiN was introduced by reactive PLD from TiN targets in low-pressure N-2. The PLD films were grown in vacuum onto room temperature substrates. The RF-MS films were deposited in low-pressure argon on substrates heated at 550 degreesC. The initially amorphous PLD thin films were annealed at 550 degreesC for 1 h in ambient air in order to restore the initial crystalline structure of HA target. The thickness of the PLD and RF-MS films were similar to1 mum and similar to350 nm, respectively. All films were structurally studied by scanning electron microscopy (SEM), grazing incidence X-ray diffraction (GIXRD), energy dispersive X-ray spectrometry (EDS) and white light confocal microscopy (WLCM). The mechanical properties of the films were tested by Berkovich nano-indentation. Both PLD and RF-MS films mostly contain HA phase and exhibit good mechanical characteristics. Peaks of CaO were noticed as secondary phase in the GIXRD patterns only for RF-MS films. By its turn, the sputtered films were smoother as compared to the ones deposited by PLD (50 nm versus 250 nm average roughness). The R-F-MS films were harder, more mechanically resistant and have a higher Young modulus. (C) 2004 Elsevier B.V. All rights reserved.

4222. Preparation and characterization of Ce-doped BaTiO3 thin films by pulsed laser deposition

Authors: Cernea, M; Ianculescu, A; Monnereau, O; Argeme, L; Bley, V; Bastide, B; Logofatu, C

Published: APR 15 2004, JOURNAL OF MATERIALS SCIENCE, 39, 2759, DOI: 10.1023/B:JMSC.0000021450.39778.81

Thin films of BaTiO3 doped with 5.5 mol% CeO2 have been deposited on Pt/Si substrate by pulsed laser deposition. These films crystallize on the tetragonal BaTiO3 structure without any preferential orientation. Ce-doped BaTiO3 films deposited by PLD at 675degreesC in 30 Pa ambient oxygen exhibits a smooth surface: mean surface roughness (Rms) of 48 nm, mean size of grain of similar to40 Angstrom, average size of aggregates of similar to 315 nm. Thin films as prepared presented good dielectric characteristics: dielectric constant and dielectrics loss ( tan delta) at a frequency of 1 KHz were 220 and 0.2, respectively. The temperature dependence of dielectric constant exhibited a diffuse ferroelectric to paraelectric phase transition at about 0 - 10degreesC. The ferroelectric nature of Ce-doped BaTiO3 film was confirmed by the hysteresis of the C-V curves. (C) 2004 Kluwer Academic Publishers.

4223. Quantitative determination of the volume fraction of intergranular amorphous phase in sintered silicon nitride

Authors: Roebben, G; Sarbu, C; Lube, T; Van der Biest, O

Published: APR 15 2004, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, 370, 458, DOI: 10.1016/j.msea.2003.05.004

In this paper, a commercial liquid phase sintered silicon nitride with Y2O3 and Al2O3 additives is investigated. The material is characterised by a large, and stable, internal friction peak near H 50 degreesC. The peak is linked with the glass transition in intergranular amorphous volumes, whose presence is confirmed with transmission electron microscopy. An estimate of the volume fraction of the amorphous phase is calculated from the difference in stiffness below and above the glass transition temperature. The procedure relies on accurate Young's modulus data, which were obtained with the impulse excitation technique (IET). The amount of amorphous pocket phase was estimated at 12.4 vol.%. For the first time, microstructural evidence supporting this estimate is obtained, using analysis of scanning electron microscopy (SEM) images. The rather large amount of amorphous matter explains the limited high temperature potential of the material, which was primarily and successfully developed for wear applications. (C) 2003 Elsevier B.V. All rights reserved.

4224. On the optical properties of micro- and nanometric size PbI2 particles

Authors: Baibarac, M; Preda, N; Mihut, L; Baltog, I; Lefrant, S; Mevellec, JY

Published: APR 7 2004, JOURNAL OF PHYSICS-CONDENSED MATTER, 16, 2356, DOI: 10.1088/0953-8984/16/13/014

Scanning electron microscopy, Raman scattering, UV-VIS absorption spectroscopy and low temperature photoluminescence (PL) were used to examine small particles produced by the chemical reaction between Pb(NO3)(2) and KI in different liquid media: water, methanol, ethanol and acetonitrile. By stoichiometric changes in the synthesis reaction, platelets of PbI2 and rods probably of KPbI3 are produced. Regardless of shape and size, these particles exhibit almost the same PL, which consists of two intense bands centred around the 2.5 (E band) and 2.0 eV (G band), in turn similar to that of a crystalline slide or a micrometric powder, both prepared from a PbI2 single-crystal grown from the melt. Crystalline PbI2 platelets exhibit an E band with two components, at 2.49 (E-F band) and 2.47 eV (E-T band), originating in the recombination of the free and trapped excitons produced by inter-band irradiation. A close relation between the enhancement of the E-T and G band reveals that they are linked to the surface defects. For the rod-like particles, the PL spectrum is somewhat similar to that of a Pb2+ ion introduced into an alkaline halide lattice, which as for any ns(2) ion displays two emission bands, A(T) and A(X), whose correspondents are E and G bands.

4225. Pulsed laser deposition of biocompatible polymers: a comparative study in case of pullulan

Authors: Cristescu, R; Stamatin, I; Mihaiescu, DE; Ghica, C; Albulescu, M; Mihailescu, IN; Chrisey, DB

Published: APR 1 2004, THIN SOLID FILMS, 453, 268, DOI: 10.1016/j.tsf.2003.11.145

We report some results of a comparison between thin films of pullulan biopolymer obtained by pulsed laser deposition (PLD) and matrix-assisted pulsed laser evaporation (MAPLE). In experiments we used a KrF* laser source generating pulses of 248 nm and 20 ns pulse duration. We demonstrate by Fourier transformed infrared spectroscopy (FTIR) that MAPLE is more appropriate than conventional PLD for transfer with high structural fidelity of biopolymers from target to substrate. In case of MAPLE, besides FTIR spectra, atomic force microscopy micrographs and scanning electron microscopy images prove that the film composition and structure strongly depend on the solvent used for the targets preparation: distilled water, ethylene glycol, ethanol, tert-butanol and dimethyl sulfoxide. Our best results for pullulan deposition were obtained using dimethyl sulfoxide as a solvent. This is the first report of successful MAPLE deposition of this material as thin films. (C) 2003 Elsevier B.V. All rights reserved.

4226. Anomalies of AC susceptibility losses in the doped [Bi(Pb)](2)Sr2Ca2CU3Ox superconductor

Authors: Mihalache, V; Aldica, G; Badica, P; Crisan, A

Published: APR 2004, SUPERCONDUCTOR SCIENCE & TECHNOLOGY, 17, 730, DOI: 10.1088/0953-2048/17/4/030

AC susceptibility measurements have been performed on Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox (Bi-2223) samples doped with different Li-based compounds and prepared by the solid-state method. As-prepared samples and/or samples annealed in oxygen or argon, ground or unground, have been investigated in detail in order to understand the occurrence, nature and evolution of the anomalous peaks observed in chi " (T) curves versus the measuring parameters; we have detected up to four peaks instead of the usual two peaks observed in the non-doped samples. It was found that intrinsic physical-chemical properties, such as the melting temperature of the doping compound, are no less important for the final properties of the superconductor than their insertion properties into the crystal lattice of Bi-2223. Doping compounds with melting temperatures below or close to the phase formation temperature of the Bi-2223 phase can act as flux, changing the growth conditions. Intensification of some processes against others (e.g. decomposition-recovery of the BI-2223 phase, solubilization-precipitation of the secondary phases, changes in the properties of the liquid phase, etc) can lead to the formation of the Bi-2223 phase with different properties than for the non-doped superconductor. Generally, when using flux-type doping compounds, anomalous AC losses peaks are detected and the intra-granular critical current density is enhanced.

4227. The first specimen of tetranuclear (Fe-III, Ln(III)) clusters assembled by carboxylate ligands: synthesis, structure, Mossbauer spectra, and magnetic properties of [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)]center dot THF

Authors: Turta, C; Prodius, D; Mereacre, V; Shova, S; Gdaniec, M; Simonov, YA; Kuncser, V; Filoti, G; Caneschi, A; Sorace, L

Published: APR 2004, INORGANIC CHEMISTRY COMMUNICATIONS, 7, 579, DOI: 10.1016/j.inoche.2004.02.025

The reaction of the neutral cluster [Fe2BaO(CCl3COO)(6)(THF)(6)] with Eu(NO3)(3) . 6H(2)O in methanol affords novel tetra-nuclear Fe-Eu complex [Fe3EuO2(CCl3COO)(8)H2O(THF)(3)] . THF (1), which displays interesting Mossbauer spectra and magnetic behaviour. (C) 2004 Elsevier B.V. All rights reserved.

4228. Chemical growth of calcium phosphate layers on magnetron sputtered HA films

Authors: Verestiuc, L; Morosanu, C; Bercu, M; Pasuk, I; Mihailescu, IN

Published: MAR 15 2004, JOURNAL OF CRYSTAL GROWTH, 264, 491, DOI: 10.1016/j.jcrysgro.2004.01.015

Chemical growth of calcium phosphate films on top of apatite structures is an essential step for promoting implants integration in human bones. We used for chemical growth silicon wafers either covered with crystalline and amorphous hydroxyapatite films or uncoated. To promote growing, the structures have been immersed in simulated body fluids for 21 days at 37degreesC. The growth stages were monitored by atomic spectroscopy of Ca and P ions in solution. The calcium phosphate deposits were investigated by X-ray diffraction, optical and atomic force microscopy and FTIR spectroscopy. The grown structures onto sputtered hydroxyapatite were amorphous and smooth. The depositions performed directly on silicon substrates are mild. (C) 2004 Elsevier B.V. All rights reserved.

4229. Mossbauer study of the RENiSnD (RE : Pr, Nd) monodeuterides

Authors: Spataru, T; Principi, G; Kuncser, V; Keune, W; Yartys, VA

Published: MAR 10 2004, JOURNAL OF ALLOYS AND COMPOUNDS, 366, 85, DOI: 10.1016/S0925-8388(03)00744-8

NdNiSnD and PrNiSnD monodeuterides have been studied by Sn-119 Mossbauer spectroscopy at variable temperatures between 4.2 and 300 K. Deuterium insertion into the RE3Ni sites induces at low temperatures a magnetic splitting of the tin nuclear levels. Slightly different magnetic ordering temperatures, 25(1) and 20(1) K, were evidenced for the Nd- and Pr-containing deuterides, respectively. The Mossbauer spectra suggest a similar type of local structures for both compounds, with a mutual substitution of Sn and Ni atoms. The magnetic behaviour is discussed in relation to the different spin waves mechanisms. (C) 2003 Elsevier B.V. All rights reserved.

4230. Carbon material deposition by remote RF plasma beam

Authors: Mitu, B; Vizireanu, S; Petcu, C; Dinescu, G; Dinescu, M; Birjega, R; Teodorescu, VS

Published: MAR 1 2004, SURFACE & COATINGS TECHNOLOGY, 180, 243, DOI: 10.1016/j.surfcoat.2003.10.147

Hydrogenated and nitrogenated carbon films were obtained by PECVD with carbon species supplied by acetylene gas injected into an argon or argon/nitrogen remote plasma generated by an expanding radiofrequency discharge. The properties of carbon material like the nature of bonds, morphology, surface topography, crystallinity are presented. The reaction pathways linking the precursors with the depositing species, as revealed by emission spectroscopy, are discussed. (C) 2003 Elsevier B.V. All rights reserved.