National Institute Of Materials Physics - Romania

Publications

5781 articles found

4261. New planar compact dual mode filters for mobile communications

Authors: Banciu, MG; Lojewski, G; Ioachim, A; Nedelcu, L; Militaru, N; Shen, A; Ramer, R

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 140, DOI:

A new type of dual mode filter is proposed for mobile communications systems in 900 MHz frequency bandwidth such as GSM or GPRS. The planar filters were developed on a 0.635 mm substrate with a 10.8 dielectric constant. Several methods of modes coupling were investigated. Each dual mode resonator has a square-shape with the edge 20.5 mm and contributes with two poles to the filter response.

4262. Electric and ferroelectric properties of Pb(Zr0.2Ti0.8)O-3 thin films deposited by pulsed laser deposition on single crystalline substrates

Authors: Pintilie, L; Lisca, M; Alexe, M

Published: 2004, 2004 International Semiconductor Conference, Vols 1and 2, Proceedings, 418, DOI:

Epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin films were grown on single crystalline Nb-doped SrTiO3 (STON) substrates by Pulsed Laser Deposition (PLD). The top electrode was SrRuO3. The investigated electric and ferroelectric properties have revealed a strong asymmetry of the two PZT-electrode interfaces. A qualitative explanation based on the possible existence of a n(+) - p junction at the STON-PZT interface is suggested.

4263. Poly (vinyl-alcohol) films for microphotonics

Authors: Obreja, P; Cristea, D; Budianu, E; Gavrila, R; Kusko, M; Kuncser, V

Published: 2004, 16TH INTERNATIONAL CONFERENCE ON MICROELECTRONICS, PROCEEDINGS, 679, DOI:

The paper presents experimental results concerning the influence of additives from a solution of the PVA on the optical properties of the polymer. The refractive index of the poly (vinyl-alcohol) was modified through the addition of inorganic materials and showed values between 1.5 and 2 (depending on the compositions and the curing conditions of the polymer. The transmittance indicated values above 80%. The additives we used were metal oxides/inorganic salts. The composition and the deposition processes were optimized to allow a better control of the optical parameters (refractive index, transmittance), to reduce the processing temperatures and to improve photosensitivity. PVA with these new light-sensitive compositions can be easily spin coated onto variety of semiconductor substrate and directly patterned. A process was developed for channel waveguides fabrication.

4264. Naturally generated beams by quasi-optical phenomena

Authors: Branescu, M

Published: 2004, FREE AND GUIDED OPTICAL BEAMS, 235, DOI: 10.1142/9789812702531_0024

The paper describes the specific quasi-optical phenomena involved in the generation of the celestial and biological radiation. It examines the generation of the free space and guided biological beams in the presence of the ambient celestial primordial isotropic background. Josephson and Kerr mechanisms provide an explanation of the concept of bio-coherence as a novel possibility of electromagnetic communication.

4265. A study of the corrosion inhibition of carbon-steel in dilluted ammonia media using 2-mercapto-benzothiazol (MBT)

Authors: Samide, A; Bibicu, I; Rogalski, M; Preda, M

Published: 2004, ACTA CHIMICA SLOVENICA, 51, 136, DOI:

The inhibiting effect of MBT has been studied regarding the corrosion of carbon-steel in diluted ammonia solution at room temperature. The effects of the inhibitor have been demonstrated using weight loss and electrochemical measurements. The increase of the inhibitor concentration leads to a decrease in the corrosion rate and in the corrosion current. The microscopic analysis of the surface of the electrode shows a decrease of the corrosion spots with the increase of the MBT concentration. This indicates a good adsorbability of MBT on the metal surface. Mossbauer spectrometry shows the formation of a superficial film on the surface of the corroded sample in the presence of MBT. This film provides a good corrosion protection for the sample.

4266. Piezoelectric and optical properties of Sr-doped PT-PZ-Pb(Mg1/3Nb2/3)O-3 ceramics

Authors: Dimitriu, E; Ramer, R; Ghica, C; Iuga, A; Ghiordanescu, V

Published: 2004, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 24, 1708, DOI: 10.1016/S0955-2219(03)00478-3

Ceramics in the ternary system (Pb,Sr)TiO3-PbZrO3-Pb(Mg1/3Nb2/3)O-3, in the ratio 85.976/5.817/8.207 mol%, was prepared by mixed oxide route. With about 13.98 at % Sr+2, as isovalent substitution in A-position of the lead titanate, high-density samples were obtained for the sintering temperatures of about 1220 and 1230 degreesC. Tetragonal phases were identified both by XRD method and selected area electron diffraction pattern (SAED). The lattice parameter ratio, c/a, of about 1.017 indicated a decrease of tetragonal distortion. The typical TEM micrographs showed domains of about 50 nm wide. The reflection spectra were recorded to prove the presence of the transition Ti+4 to Ti+3. The principal mechanical, electrical and electromechanical properties were discussed as a function of the sintering temperature. The variation of the relative constant with the temperature and frequency evidenced a relaxation-like behavior of this ternary system. By combining the ferroelectric and relaxor end member we tried to improve the piezoelectric properties of a ceramic with a high content of lead titanate, and to achieve a material with both piezoelectric and relaxor-like properties. (C) 2003 Elsevier Ltd. All rights reserved.

4267. Structural and magnetic properties of polypyrrole nanocomposites

Authors: Turcu, R; Peter, I; Pana, O; Giurgiu, L; Aldea, N; Barz, B; Grecu, MN; Coldea, A

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 417, 727, DOI: 10.1080/15421400490478939

We report the synthesis and characterization of conducting polymer nanocomposites based on polypyrrole (PPY) and Fe2O3 magnetic particles. The global structure of PPY nanocomposites was obtained by X-ray Diffraction (XRD) method using a new approximation based on Generalized Fermi Function. The local structural parameters of Fe sites in Fe2O3 nanocrystallites embedded in PPY were determined by X-ray Absorption Spectroscopy (EXAFS). The lack of hysteresis loop for the magnetization curves of the composite PPY-Fe2O3 indicates a superparamagnetic behavior which is typical for nanosized magnetic particles.

4268. Microstructure of Si/Sio(2) nanocomposite films

Authors: Teodorescu, VS; Ciurea, ML; Iancu, V; Blanchin, MG

Published: 2004, 2004 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1AND 2, PROCEEDINGS, 62, DOI: 10.1109/SMICND.2004.1402802

The paper presents the inicrostructure of the Si/SiO2 nanocomposite films prepared by co-sputtering from Si and SiO2 targets. High resolution transmission electron microscopy and electron diffraction were used to reveal and compare the structures with different silicon/oxygen (SiOx, 0 < x < 2) coinposition. Si nanocrystallites have been evidenced clearly in the SiO1.6 areas. Percolation limits between the Si crystallites was observed in the x=1 areas. The morphology of the Si nanocrystallites and the amorphous SiO2 zones were compared in regions with different composition.

4269. Confining effects in composites containing molecular sieves

Authors: Frunza, L; Frunza, S; Enache, I; Beica, T; Schonhals, A; Kosslick, H; Bentrup, U; Pitsch, I

Published: 2004, MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 418, 813, DOI: 10.1080/15421400490479145

Confinement of 4n-octyl-4'-cyanobiphenyl to nanoporous molecular sieves with hexagonal structure of cylindrical pores or with cellular structure is studied. It was found by differential scanning calorimetry and broadband dielectric spectroscopy that composites with the pores completely filled with liquid crystal show phase transitions characteristic for bulk, while the partially filled samples do not show these transitions. Thermogravimetric, differential thermal analysis and in situ infrared spectroscopic investigations have indicated first time that the dealkylation and oxidation of the confined liquid crystal is quite possible inside the nanopores of these molecular sieves, at temperatures much lower than for the bulk.

4270. Epoxidation of cyclohexene on silicalite embedded BiOx clusters

Authors: Parvulescu, VI; Florea, M; Gelbard, G; Centeno, MA; Macovei, D; Lemay, G; Kaliaguine, S

Published: 2004, RECENT ADVANCES IN THE SCIENCE AND TECHNOLOGY OF ZEOLITES AND RELATED MATERIALS, PTS A - C, 154, 2654, DOI:

Silicalite embedded BiOx Clusters were prepared both with and without Na using sodium silicate and tetraethylorthosilicate as silicium precursors. Catalysts with 3 and 5 wt% Bi were obtained. The MFl structure was established from XRD, TEM, and N-2 adsorption measurements. No deterioration of the silicalite framework by bismuth was observed. Bi exists as BiOx clusters as evidenced from XPS and EXAFS characterization. These clusters are localized inside the silicalite channels. Py-FTIR measurements indicated that 5wt% Bi led to the formation of strong Lewis acid sites. Epoxidation of cyclohexene was found to depend oil both Bi and Na content. On 3%Bi-ZSM-5 it occurred with rather good conversion and selectivity to epoxide. No visible leaching was evidenced. The catalysts were reused for several runs.