National Institute Of Materials Physics - Romania

A comparative study of photodetector performance for nano- and micro-crystalline PbS thin layers is presented Both types of PbS films were obtained using the Chemical Bath Deposition method. To prepare nano-crystalline thin films we used a short reaction time with no doping Bi added At low levels of irradiance (0.1 mW/cm(2)) and room temperature (RT), the macro-crystalline PbS outperforms its nano-crystalline counterpart, by a factor of 6 for the value of Delta R/R-dark. However the nano-crystalline photodetectors show significantly lower optical quenching for large values of irradiance (approximate to 500 mW/cm(2)) at RT and better Delta R/R-dark performance at lower temperature, with an optimum temperature Of 150 K. The low frequency noise behavior is a superposition of 1/f flicker noise at low frequency and generation-recombination and thermal noise at higher frequency. The proportionaliiy factor between the 1/f noise and the DC dark current for the series resistor is 1.5 times larger for the nano-crystalline photodetector at room temperature.

Three types of materials for dielectric resonators are presented in this paper. The Pb-BNT materials show the highest dielectric constant (similar to 85). A very small controllable temperature coefficient if in the range (-2 divided by +4) ppm/degrees C can be achieved by using dielectric resonators Mg-(Zr0.8Sn0.2)TiO4. On the other hand, the resonators made of Ba(Zn1/3Ta2/3)O-3 exhibit the highest values for the Qxf product, ranging from 50000 to 130000 GHz, which make them attractive for millimetre wave applications.

An extensive investigation of the gold ores in the South Carpathians (Costesti, Valea lui Stan si Jidostita) has performed, using different chemical and physics experimental techniques. The used structural techniques have been the electron microscopy, X-ray diffraction, Mossbauer effect and electron spin resonance. The investigation of the representative samples by the structural techniques relieved new minerals in the gold ores, the presence of the "coral like" aggregates of nanometric gold solid bubbles.

The cobalt oxide superconductor NaxCoO2 center dot yH(2)O is studied by angle-resolved photoemission spectroscopy. We report the Fermi surface (FS) topology and electronic structure near the Fermi level (E-F) in the normal state of NaxCoO2 center dot yH(2)O. Our result indicates the presence of the hexagonal FS centered at the Gamma point, while the small pocket FSs along Gamma-K direction are absent, similar to NaxCoO2. The top of the e(g)(') band, which is expected in band calculations to form the small pocket FSs, extends to within similar to 30 meV below E-F, closer to E-F than in NaxCoO2. We discuss its possible role in superconductivity, comparing with other experimental and theoretical results.

Magnetic properties of FePt/Ag/Fe and FePt/Pd/Fe layer systems, prepared by magnetron sputtering, were investigated using the nuclear resonant forward scattering of synchrotron radiation. This technique allows the accurate determination of magnetic hyperfine field orientations by using an extremely thin 57 Fe probe layer suitably embedded within the soft magnetic layer. From an evaluation of these measurements within a one-dimensional micromagnetic model, the interlayer exchange coupling constants between the magnetically hard (FePt) and soft (Fe) layers were determined as function of the Ag and I'd interlayer thickness. The interlayer thickness dependence of the bilinear coupling constants provides evidence for the superposition of Ruderman-Kittel-Kasuya-Yoshida coupling and a magnetostatic interaction between the magnetic layers. (c) 2006 Elsevier B.V. All rights reserved.

Phosphosilicate films with 90%SiO2-10%P2O5 molar composition, derived from tetraethoxysilane as SiO2 precursor and triethylphosphate, triethylphosphite or phosphoric acid as P2O5 precursors were prepared using the sol-gel method. The films were deposited on glass and ITO coated glass supports. The influence of the type of P2O5 precursor, type of substrate and of the thermal treatment (200, 300 and 500 degrees C) on their structure and properties was studied. By spectroellipsometric and XPS measurements the high vaporization of the phosphorous during the densification of the films by thermal treatment was noticed when alkoxide were used, underlying that the mentioned precursors are not recommended for thin phosphosilicate films preparation. The phosphoric acid that forms chemical bond with silica network during the sol-gel process lead to better incorporation of P in the silica network as compared to the P-alkoxides.

Thin films having ZnO nanocrystallites, with a minimum average size of 2.2 nm, embedded in an amorphous gold oxide matrix have been investigated. These structures do not present a blue-shift of the absorption spectra relative to those corresponding to large ZnO crystallites, a shift which would be expectable for this range of particle size. It was found that the hydrated gold oxide has a much narrower energy gap than ZnO and does not creates quantum wells in the ZnO crystallite region. The Raman spectra present only the confined vibration modes of ZnO. These peculiarities of the mixed system were analyzed by means of an adequate energy band diagram. A Raman resonant effect, determined by interface transitions, has also been detected.

The magnetic nanocomposite materials represent an important class of nanomaterials extensively studied nowadays due to their varied applications from medical diagnostic to storage information. The iron oxides in silica matrix systems are highly investigated. The sol-gel method is a suitable way of preparation of Fe3O4-SiO2 nanocomposite materials, since this method allowed the preparation of nanocomposite materials with narrow size distribution of magnetite in silica matrix. In the present work, nanocomposite materials in the Fe3O4-SiO2 system were prepared by sol-gel method via alkoxide and aqueous route. As SiO2 sources, tetraethoxysilan (TEOS) for the alkoxide route, as well as silica sol Ludox (30%) for the aqueous route, were used. This study shows the influence of the type of silica matrix on the structure, size, and distribution of the Fe3O4 nanoparticles in the Fe3O4-SiO2 systems. The gels were annealed at 550 degrees C in order to consolidate the matrices. The structural characterization of the obtained materials via the two preparation routes was performed by DTA/TGA analysis, X-ray diffraction, IR and Mossbauer spectroscopy, Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED).

It is shown that self-organization in non-crystalline networks of amorphous semiconductors, as well as in non-crystalline chalcogenide materials is rather a rule than an exception. The fundamental principles are stated on the basis of few examples. The most extended order in glasses is given by the uniform distribution of large stochastic clusters.