National Institute Of Materials Physics - Romania

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5781 articles found

3871. Band-pass filters with (Zr-0.8, Sn-0.2)TiO4 dielectric resonators

Authors: Ioachim, A; Banciu, MG; Nedelcu, L; Dutu, CA

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 943, DOI:

Band-pass filters with dielectric resonators of (Zr-0.8, Sn-0.2)TiO4 ceramic materials (ZST) were developed for X-band applications. The ZST materials exhibit a dielectric constant of about 36.8 and low loss in microwave range. A Qxf product higher than 50,000 was achieved for the ZST samples with 0.2 % wt NiO sintering addition. The external coupling was performed using microstrip lines on a substrate of 9.22 dielectric constant and 0.635 mill height. Filters with a minimum insertion loss between 0.46 dB and 1.74 dB, the bandwidth between 40 MHz and 170 MHz and with the central frequency around 10 GHz were manufactured.

3872. Optical properties of polycarbonate organic matrix/cadmium sulphide clusters composite material

Authors: Stanculescu, A; Stanculescu, F; Socol, M

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1061, DOI:

This paper presents the investigation of the optical properties of bisphenol A polycarbonate organic matrix/CdS clusters composite material in correlation with the method for the films' preparation using as precursors cadmium acetate (Cd(CH3COO)(2)), respectively ammonium thiocyanate (NH4CNS), and as general solvent for all the components, is dimethyformamide. The effect of the heat treatment temperature (90 degrees C or 150 degrees C) on the position and shape of the fundamental absorption edge was investigated for given substrate, drying conditions and duration (1.5 h or 0.5 h) of the heat treatment. A large blue shift of the absorption edge was evidenced in films prepared in vertical configuration and thermally treated at 90 degrees C for 1.5 h, which can be associated with a small dimension of the CdS crystallites and in consequence with quantum confinement effects. Using the effective mass theory we have deduced a crystallite dimension in the range 8.8-15 nm. We also have studied the interaction of the light with this composite material evaluating an optical band gap between 2.92 and 3.69 eV (depending on the preparation and annealing conditions) and an absorption mechanism in CdS clusters closer to an indirect transition and deviated from the normal direct absorption process in bulk CdS semiconductor.

3873. TiO2 thin films doped by Ce, Nb, Fe, deposited onto ITO/glass substrates

Authors: Mardare, D; Apostol, E

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 916, DOI:

Optical transmittance studies were carried out on some doped titanium dioxide thin films, obtained by r.f. magnetron reactive sputtering, using glass and ITO/glass substrates. We have observed that, while TiO2 films have a good transparency till about 2000 nm, the ensemble TiO2 and ITO (indium tin oxide) films gives a decrease of the optical transmittance in near infraread region, being still transparent in the visible range. The mentioned decrease depends on the dopant used. This is an important observation, since TiO2 films are already used as coatings for many buildings. So, for economic reasons, the necessary energy used for the inside cooling of the air can be reduced, by getting a good visible transparent window, together with a NIR shielding.

3874. Fractal structures of gold obtained by diffusion limited aggregation in alkali halide crystals

Authors: Enculescu, M; Enculescu, I; Topa, V

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1233, DOI:

Nanostructures of gold embedded in potassium chloride matrices were obtained after the doped crystals growth, by electrolytical colouring, and by thermal treatment. When the TEM images of the nanostructures were analyzed using fractal geometry it means was proved that the self assembling of the metallic structures is governed by the diffusion limited aggregation (DLA) mechanism. The values of the fractal dimension, which were in all cases between 1.7 and 1.9, calculated using two methods, sandbox and box-counting, proved the DLA mechanism.

3875. Optical and electronic properties of (Fe+Sb): PVA for real time holography

Authors: Kuncser, V; Bulinski, M; Krautwald, S; Franke, H; Wagner, FE; Cristea, D; Palade, P; Plapcianu, C; Filoti, G

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1229, DOI:

The electron transfer processes induced by the ultraviolet exposure of the Fe and Sb doped polyvinyl alcohol (PVA) thin films were studied in comparison with those appeared in the correspondent mono (Fe or Sb) doped ones. Samples with different thickness and subjected to different exposures were analysed by optical absorption as well as by Fe-57 and Sb-121 Mossbauer spectroscopy. The influence of each element from the pair on the electronic mechanism activated by the ultraviolet exposure was investigated. Accordingly, the (Fe+Sb) doped PVA presents improved electronic characteristics, in respect to the specific behaviour of single metal doped polymer recording media for real time holography.

3876. Paramagnetic defects in amber-colored superhard c-BN crystalline powders

Authors: Nistor, SV; Goovaerts, E

Published: JUN 2006, HIGH PRESSURE RESEARCH, 26, 117, DOI: 10.1080/08957950600765285

Two samples of large-grained commercial superabrasive cubic boron nitride crystalline powders in different shades of amber coloration have been investigated by low frequency X (9.4 GHz)-band electron paramagnetic resonance (EPR) spectroscopy at room and low (T < 15 K) temperatures. Both samples contain three spectra component lines, A1, A2 and A3, in the same proportion, and the total concentration of the corresponding paramagnetic centers being proportional to the intensity of the amber coloration. After in situ broad-band UV illumination at low temperature, the intensity of the A1 component line becomes dominant. The observed effects are attributed to electron trapping at EPR silent A1(+) precursor centers, which seem to coexist with the A1 centers and to the eventual ionization of the paramagnetic A3 centers responsible for the A3 component line.

3877. Light absorption in meta-dinitrobenzene and benzyl crystalline films

Authors: Stanculescu, F; Stanculescu, A; Socol, M

Published: JUN 2006, JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS, 8, 1056, DOI:

This paper presents the optical absorption properties in crystalline meta-clinitrobenzene (m-DNB) and benzil. The optical band gap as an intrinsic property of these crystalline compounds has been studied using UV-VIS Spectroscopy on thin film. Analysing absorption near the fundamental absorption edge we have deduced the wide band gap semiconductor behaviour of these aromatic derivatives. Processing the experimental transmission data using a function obtained by the superposition of a linear function and a power function we have evaluated the band gap energy in m-DNB, E-g=2.90 eV and emphasised the same two edges patterns of the light absorption spectrum in benzil deposited on glass as for benzil deposited on quartz, with energetic thresholds slowly moved through lower energies, E-g1=2.79 eV and E-g2=3.49 eV. We have also remarked no significant change in the absorption spectrum in benzil induced by the dopant (organic and inorganic).

3878. Laser ablated Fe100-xPdx and Fe100-xMnx thin films (x=20 and 50)

Authors: Sorescu, M; Diamandescu, L; Grabias, A

Published: JUN 2006, INTERMETALLICS, 14, 783, DOI: 10.1016/j.intermet.2005.11.010

Thin films (50 nm) of Fe100-xPdx and Fe100-xMnx (x=20 and 50) were deposited by laser ablation on a Si wafer and studied by X-ray diffraction (XRD) and conversion electron Mossbauer spectroscopy (CEMS). In all cases, the XRD patterns of the target surface before and after ablation show a congruent transfer of ablated material. For the Fe80Pd20 thin, film, XRD spectra show the formation of FePd, iron, Pd oxide and traces of hematite in the ablated film. Complementary information obtained by CEMS indicates the presence of an upper 50-nm thick surface layer of hematite in the deposited film. Fe50Pd50 phase was observed by CEMS and a Pd oxide component was identified by XRD, along with traces of hematite. In the case of Fe80Mn20, the CEMS spectrum is consistent with the Occurrence of the anti ferromagnetic FeMn phase and the XRD pattern also shows the presence of Fe in the structure. For the system Fe50Mn50, we obtain by CEMS an antiferromagnetic phase of FeMn and by XRD we trace the presence of nanohematite and in-depth iron. For x=20 in both iron-rich systems investigated, we observe the segregation of iron with subsequent conversion to hematite. The study shows that the stoichiometry of the compounds plays a decisive role in determining their structural and magnetic properties. (c) 2006 Elsevier Ltd. All rights reserved.

3879. Electronic transport in Si-SiO2 nanocomposite films

Authors: Ciurea, ML; Teodorescu, VS; Iancu, V; Balberg, I

Published: MAY 20 2006, CHEMICAL PHYSICS LETTERS, 423, 228, DOI: 10.1016/j.cplett.2006.03.070

We report experimental investigations and modeling of the electronic transport in Si-SiO2 nanocomposite films. The current-voltage characteristics measured at room temperature are interpreted as due to high field-assisted tunneling. The activation energies from the current-temperature curves,are given by the energy separations between quantum confinement electronic states, determined from a quantum well model. Consequently, the calculated mean diameter of a nanodot (5.2 nm) is in good agreement with the microstructure data (5 nm). Also, the potential barrier between nanocrystalline Si and amorphous SiO2, previously obtained for nanocrystalline oxidized porous Si (2.2 eV), is confirmed. (c) 2006 Elsevier B.V. All rights reserved.

3880. Hydrogen storage in Mg-Ni-Fe compounds prepared by melt spinning and ball milling

Authors: Palade, P; Sartori, S; Maddalena, A; Principi, G; Lo Russo, S; Lazarescu, M; Schinteie, G; Kuncser, V; Filoti, G

Published: MAY 18 2006, JOURNAL OF ALLOYS AND COMPOUNDS, 415, 176, DOI: 10.1016/j.jallcom.2005.08.017

Magnesium-rich Mg-Ni-Fe intermetallic compounds have been prepared by two different routes: (a) short time ball milling of ribbons obtained by melt spinning; (b) long time ball milling of a mixture of MgH2, Ni and Fe powders. The first type of samples displays an hydrogen desorption kinetics better than the second one. Pressure composition isotherm measurements exhibit for both type of samples two plateaux, the lower and wider corresponding to the MgH2 phase and the upper and shorter corresponding to the Mg2NiH4 phase. The presence of the two types of hydrides is confirmed by X-ray diffraction analysis. Mossbauer spectroscopy shows that in melt spun and subsequently milled samples iron is mainly in a disordered structure and segregates after hydrogenation, while in directly milled powders remains mainly unalloyed. After multiple hydrogen absorption/desorption cycles the main part of iron is in metallic state in samples of both types, those of first type preserving better hydrogen desorption kinetics. (c) 2005 Elsevier B.V. All rights reserved.