National Institute Of Materials Physics - Romania

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5975 articles found

3971. Broadband planar filters with enhanced couplings using defected ground structures

Authors: Militaru, N; Banciu, MG; Lojewski, G

Published: 2007, 2006 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, +, DOI:

In this paper a study of some microwave microstrip bandpass filters (BPF) using defected ground structures (DGS) is presented. This technique allows designs of tight couplings without the necessity of using very narrow coupling gaps. Based on the results of the study, four-pole cross-coupled planar microwave bandpass filters were designed, with a single of. with two ground slots. Compared to similar microstrip filters without defected ground, the simulated performances of these novel structures indicate some technological advantages.

3972. Aperture couplings in multilayer filtering structures

Authors: Militaru, N; Lojewski, G; Banciu, MG

Published: 2007, ISSCS 2007: INTERNATIONAL SYMPOSIUM ON SIGNALS, CIRCUITS AND SYSTEMS, VOLS 1 AND 2, +, DOI:

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.

3973. Comparative study of the mass-loading effect on electrical parameters of gallium phosphate, quartz and langasite resonators

Authors: Mateescu, I; Krispel, F; Georgescu, S; Scott, K; Borca, E

Published: 2007, PROCEEDINGS OF THE 2007 IEEE INTERNATIONAL FREQUENCY CONTROL SYMPOSIUM-JOINTLY WITH THE 21ST EUROPEAN FREQUENCY AND TIME FORUM, VOLS 1-4, +, DOI: 10.1109/FREQ.2007.4319163

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.

3974. Gas-sensing by Polymer-Iron nanocomposite materials

Authors: Tomescu, A; Simion, CE; Alexandrescu, R; Morjan, I; Scarisoreanu, M

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI:

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.

3975. Characterization of PbZrO3 prepared using an alkoxide-based sol-gel synthesis route with different hydrolysis conditions

Authors: Ion, ED; Malic, B; Kosec, M

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 4352, DOI: 10.1016/j.jeurceramsoc.2007.02.158

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.

3976. Wide band gap semiconductor SAW type devices for GHz applications, manufactured using nano-lithographic techniques

Authors: Muller, A; Dinescu, A; Konstantinidis, G; Vasilache, D; Dragoman, M; Morosanu, C; Sajin, G; Neculoiu, A

Published: 2007, CAS 2007 INTERNATIONAL SEMICONDUCTOR CONFERENCE, VOLS 1 AND 2, PROCEEDINGS, +, DOI: 10.1109/SMICND.2007.4519695

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.

3977. Triple-barrier resonant tunneling: A transfer matrix approach

Authors: Simion, CE; Ciucu, CI

Published: 2007, ROMANIAN REPORTS IN PHYSICS, 59, 817, DOI:

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.

3978. Optical studies of TiO2 films deposited on different substrates

Authors: Cotirlan, C; Vasile, V; Ungureanu, F

Published: 2007, ROMOPTO 2006: EIGHTH CONFERENCE ON OPTICS, 6785, DOI: 10.1117/12.756805

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.

3979. Influence of twin cations on zirconia composites stability

Authors: Volceanov, E; Volceanov, A; Stoleriu, S; Motoc, S; Melinescu, A; Plapcianu, C

Published: 2007, JOURNAL OF THE EUROPEAN CERAMIC SOCIETY, 27, 1387, DOI: 10.1016/j.jeurceramsoc.2006.08.003

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.

3980. Qualitative characterization of YBa2Cu3O7-delta films using low spectral resolution Raman spectroscopy

Authors: Branescu, M; Morjan, I; Dumitrache, F; Sandu, I

Published: 2007, ADVANCED LASER TECHNOLOGIES 2006, 6606, DOI: 10.1117/12.729507

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.