Publications

In this paper the problem of designing simple low-cost planar microwave bandpass filters with strongly asymmetric characteristics, filters that can very efficiently attenuate one of the two adjacent channels, is investigated. In case of a fourth-order filter, the usual quadruplet structure leads to two transmission zeros located one on each side of the passband, but higher attenuation can be obtained for one of the two adjacent channels by designing filters with two transmission zeros in the same (upper or lower) stopband. The new topology investigated in this paper offers the possibility of designing such quadruplets with two transmission zeroes situated both on the same side of the passband, in prescribed and controlled positions. Filters with this novel structure can provide very high attenuation not only at a single frequency, but in a larger adjacent frequency band.

The structure of nano-carbon objects (ball-like, nanotubes, defected graphenes) has been modeled by a Monte-Carlo computer procedure. The structure of nano-chalcogenides objects based on two-dimensional network of arsenic sulphide has been modeled. The results were compared to the experimental data whenever possible. The structural modelling was proved as a powerful method for predicting new nano-structural elements in various low-dimensional materials.

We show that an anisotropic periodic structure can shape an incident optical beam with a large angular divergence. This is a new application of photonic crystals, which does not require any additional energy source, such as an electric field

The purpose of this work is to compare the density of shallow interface states (D-it) at the interface of SiO2/SiC MOS capacitors as deducted by the conductance spectroscopy (CS) and thermally dielectric relaxation current (TDRC) techniques. Both capacitors of 4H- and 6H-SiC (n-type) arc investigated, and both ordinary dry oxidation and,in improved industrial procedure have been employed. The two techniques are found to give rather good agreement for interface states located >= 0.3 eV below the conduction band edge (E-c) while for more shallow states vastly different distributions of D-it are obtained. Different reasons for these contradictory results are discussed, such as strong temperature and energy dependence of the capture cross section of the shallow interface States.

Measurements by optical microscopy and spectroscopy were performed on different textile materials (yarn, woven, knitted materials) in order to get their characterization. Thus, using non-specialized classical equipment, the value of the yarn diameter can be estimated. The yarn behavior during the stretching can be directly observed. The observation of the water imbibition by following the shape and stability of a water droplet placed onto the textile material was also developed; in this way the wetting kinetics of different textile materials was obtained. In addition, the spectral properties of woven materials allowed for the study of the modifications induced by different treatments of the woven materials.

Thin films of sucrose (C12H22O11) were deposited on thin cut glass substrates by thermal evaporation technique (p similar to 10-5 torr). The surface morphology was putted into evidence by FT-IR and SEM analysis. The experimental results confirm a uniform deposition of an adherent sucrose layer. The biological tests (e.g., cell morphology and cell viability evaluated by measuring mitochondrial dehydrogenise activity with MTT assay) confirm the properties of sucrose thin films as bioactive material. The human fetal osteoblast system grown on thin sucrose film was used for the determination of cell proliferation, cell viability and cell morphology studies.

Microstrip structures with left-handed properties are investigated in frequency domain. A method of extracting material effective parameters from the two-port scattering parameters is developed and applied to the proposed left-handed structures.

Nitrogen doped 4H-SiC epitaxial layers grown by hot-wall chemical vapor deposition were investigated by deep level transient spectroscopy after irradiation with 6 MeV electrons or 1.6 MeV protons. The influence of silane and propane flows used during the epilayers growth on the behaviour of radiation induced EH6,7 levels is studied. Samples grown under different conditions were investigated: 1 sample grown in steps of different C/Si ratio obtained by changing the propane flow only; 1 sample grown in steps of different C/Si ratio obtained by changing the silane flow only; 2 samples grown with a C/Si ratio of 1.5 but with different flows of propane and silane. These investigations revealed that the low thermal stability of EH6,7 (the defects anneal out at temperatures as low as 750K) is due to the magnitude of silane now used during the growth irrespective of the C/Si ratio. A possible structure of the EH6,7 defect is discussed.

On a superconducting bi-layer with thickness much smaller than the penetration depth, lambda, a vortex molecule might form. A vortex molecule is composed of two fractional vortices and a soliton wall. The soliton wall can be regarded as a Josephson vortex missing magnetic flux (degenerate Josephson vortex) due to an incomplete shielding. The magnetic energy carried by fractional vortices is less than in the conventional vortex. This energy gain can pay a cost to form a degenerate Josephson vortex. The phase diagram of the vortex molecule is rich because of its rotational freedom. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.

In this paper results concerning the changes of the electric characteristics of langasite resonators irradiated with electron and gamma rays are reported. For both electron and gamma irradiations the quality factor increases significantly, presumably due to the re-distribution of the point defects. Preliminary optical investigations in UV-VIS domain confirm the modification of defect structure.