Publications

In multilayer structures apertures in metallic sheets can be used as coupling elements between resonators located on different layers, allowing very compact filter designs. In this paper, some novel types of planar microwave bandpass filters, using aperture couplings, in structures with three metallic layers, are considered. Couplings between two miniaturized resonators are investigated, by full electromagnetic field simulation. Based on the results of this study, several models of planar microwave bandpass filters, with a single or with two apertures, are designed, verified by simulation, fabricated and measured. Compared to the classical filters, these novel structures show a good compactness and can offer some technological advantages.

This paper presents some of the more relevant results concerning the mass-loading influence on the characteristics (effective mass-loading, motional inductance, quality factor) of AT-cut quartz, Y-cut langasite resonators and AT-cut gallium phosphate.

Electrical properties of new Polymer-Iron nanocomposite materials obtained by laser pyrolysis were investigated, in order to find applications for the detection of reducing gases. The aim of this paper was to prove the necessity of complex experimental investigation in order to point out the contribution of different types of adsorption. Usually resistance measurement cannot fully describe the surface interactions. The electron affinity changes are of real interest for in-field conditions which always involve humidity of surrounding gas-atmosphere. On the other hand, the nanocomposite materials can be a solution for specific gas-sensing properties.

PbZrO3 precursor powders were prepared from lead acetate and zirconium n-butoxide in n-butanol and hydrolysed with R-w (molar ratio of water/lead acetate) = 2 and 15 at different pH values. Upon heating the organic groups were removed in two steps for the precursor prepared at R-w = 2, and in one step at R-w = 15. The perovskite phase crystallizes at approximately 700 degrees C, irrespective of the hydrolysis conditions. (c) 2007 Elsevier Ltd. All rights reserved.

This paper presents experiments to develop SAW structures with operating frequencies in the GHz range. The experiments were developed on AlN and GaN thin films with nano-metric lines for the IDT. The nanolithography was performed at IMT with the new purchased VEGA 5136 LM SEM from TESCAN and ELPHY Plus EBL from Raith GmbH. There were obtained some very good quality inerdigitated Ti/Au structures (with 30 digits and 29 interdigits 300nm wide, 220nm high and and 200 mu m long). Lift-off techniques to remove the undesired metal were used On wafer microwave measurements of the SAW structure (performed at IMT on the new purchased Anritsu vector analyzer equipped with Suss Microtec probes), have demonstrated its functionality. It was evidenced a pronounced resonance at about 2.8GHz.

A theoretical study of resonant tunneling in multilayered heterostructures is presented based on an exact solution of the Schrodinger equation under the application of a constant electric field and a uniform magnetic field. By use of the transfer matrix approach, the transmissivity of the structure is determined as a function of the incident electron energy. The results show good agreement with other existing models as well as with the bound-state energies. The solutions obtained are exact and can be generated easily by using MathCad. Based on these calculations, a new class of resonant tunneling superlattice devices can be designed.

Titanium dioxide thin films prepared by sol-gel method and deposited on p-Si (111), n-GaAs (100) and glass have been investigated by Raman spectrometry and photoluminescence analysis. The films were annealed in the temperature range (500-800)degrees C in air. Raman scattering studies reveal the presence of Raman active modes in the calcinated TiO2 films related to anatase phase of titania. The photo luminescence spectrum presents prominent red shifted peaks (e.g. at 400 nm for TiO2/glass), where the maximum is related to the presence in titania films of defect levels corresponding to oxygen vacancies.

Last years the ternary stabilised zirconia systems attract a considerable attention as a source of materials for structural ceramics as well as for modern fuel cells. The simultaneous influence of a pair of cations (twinned) such as: Mg2+-Ca2+ and Sr2+-Ca2+ on zirconia powders stabilisation process in 1550-1750 degrees C temperature range. Samples for investigations were performed by classical ceramic method. Comparative microstructure investigations were made by SEM on sample surfaces. The XRD, FTIR analysis and EDS spectra for the considered samples are in good agreement with the determined properties of the studied compositions. (c) 2006 Elsevier Ltd. All rights reserved.

We describe our low spectral resolution Raman system that allows us to directly appreciate the quality of YBa2Cu3O7-delta (YBCO) films, obtained by pulsed laser deposition on LaAlO3 substrate. We identify the basic features of YBCO films' spectral fingerprints, validated by high spectral resolution analysis, described in previous reports. This fast and non-destructive valuable analytical tool functions at a convenient time and environment after deposition.

Pure and strontium-doped lanthanum manganite nanopowders were obtained by solution combustion method using metal nitrates as oxidants and different organic compounds as fuel (alpha-alanine, glycine, urea and semioxamazide). Different molar ratios, fuel/oxidant, were chosen to study the effect of the fuel content on the phase formation and powder properties. The complex precursors isolated before ignition of the system, were characterized by FT-IR spectroscopy and thermal analysis. After ignition, the as-synthesized powders were calcined at different temperatures for obtaining single phases. Lanthanum manganite powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), specific surface area and magnetic measurements. (c) 2007 Elsevier Ltd. All rights reserved.