Publications

Commercial wires of MgB2 with different architectures and two different heat treatments were characterized with respect to their superconducting properties (T-c, J(c), H-irr, pinning force, macro flux jumps behaviour) through magnetic measurements and were visualized by 3D x-ray micro-tomography (XRT). For a particular architecture, heat treatment conditions of 625 degrees C/3 hrs or 700 degrees C/30 min produced relatively small differences, whereas the architecture of the wires showed a strong influence on superconducting characteristics. XRT checks the integrity of the wires easily detecting in a non-invasive way 3D macro defects and shows their hidden extended shape. XRT also allows a comparative geometry analysis between similar elements (e.g. filaments or filaments-matrix interfaces) from a particular wire or from wires with different architectures. Namely, XRT shows that the geometrical perfection (defined as the degree of departure of the geometry from the designed one) of the inner MgB2 filaments from the wires with 18 elements was lower than for the outermost ones from the same wires and was also lower than for the filaments from the wires with 7 elements. It is proposed that these results of geometrical perfection correlate with better overall superconducting quality of the wires with 7 filaments (except for the stronger presence of macro flux jumps in the wires with 7 filaments).

An important parameter of deposited thin films is their adhesion to the substrate materials, we focused on the adhesion of TiO2 layer by sol-gel or sputtering onto textile substrate as checked by an ultra-sonication method. The characterization-made prior and after the tests have shown a good adherence of the nanoparticles, despite the low deposition temperature.

A family of mesoporous, self-aggregated zinc oxide materials with spherical morphologies of high crystalline quality, is obtained through a facile, additive-free polyol procedure. The forced hydrolysis of zinc acetylacetonate in 1,4-butanediol (BD), in various reaction conditions, affords ZnO materials with versatile morphologies and optical properties. The reaction parameters (temperature, time and zinc source concentration) modulate the ZnO nanocrystallites size (from 8.1 to 13.2 nm), the spheres diameter (ranging from 50 up to 250 nm), the internal structure of the spherical aggregates (hollow or solid) and their specific surface area (from 31 to 92 m(2) g(-1)). Polycrystalline spheres with hollow cores are obtained at the lowest temperature (90 degrees C) and zinc cation concentration (0.1 M), while at higher reaction temperatures (140-180 degrees C), solid spherical aggregates are developed. A reaction mechanism for ZnO formation via zinc layered hydroxide (LDH-Zn) is proposed based on nuclear magnetic resonance (H-1 NMR and C-13 NMR) and powder X-ray diffraction (XRD) studies. The obtained ZnO materials have a functionalized surface, derived from the polyol and act as a nitrogen selective photocatalyst in the reduction reaction of NO3-. The organic residual attached on the ZnO surface plays a crucial role in the denitrification reaction, since the photo-cleaned sample showed negligible photocatalytic activity. The ZnO materials also exhibited microbicidal and anti-biofilm activity against reference and clinical strains, highlighting their potential for the development of novel antimicrobial formulations.

An amplification of near three orders of magnitude was observed in Pb(Zr,Ti)O-3 (PZT) thin films deposited on Pt/Si substrates when the Si substrate is included as an impedance in series with the PZT capacitor. The effect is present only at wavelengths below 1100 nm, where the incident light can be absorbed in the Si substrate with generation of free carriers. These carriers in turns modulate the internal electric field inside the ferroelectric layer leading to a much larger variation of the polarization compared to the one generated only by the temperature variation. This fact leads to a considerable enhancement of the pyroelectric signal. The finding can be useful in designing pyroelectric detectors with enhanced characteristics for visible and near infrared region of the electromagnetic spectrum.

The effects of strain field are studied in Si wafers implanted with heavy iodine and bismuth ions and in multi-quantum well structures. The experimental method of thermally stimulated currents without applied bias is used, and the trapping centres parameters are determined by modelling the discharge curves. In both cases, the strain field produces temperature-dependent parameters of trapping levels. So, due to the high strain field in the neighbourhood of implanted ions, energy levels broaden and cross sections become temperature dependent. In multilayer structures, for the trapping centres corresponding to strain-induced defects both concentrations and capture cross sections are temperature dependent.

Lamellar crystal objects such as straight, curved or kinked whiskers, bows and objects with missing stripes were grown in a static air atmosphere from melt-quenched substrates with starting composition Bi1.5Sr1Ca1Co0.6Oy. The average EDS composition of the objects is Bi2Sr0.75Ca1.8Co1.94Oy and the crystal structure is of the phase usually denoted in the literature as Bi-2(Sr,Ca)(2)Co2Oy (BiCO222). Objects of other phases were not found. Curvature is in the (ab)-plane. By scanning tunneling spectroscopy (STS) a semiconducting energy gap was determined at 2.41 eV.

We report the pressure vs area isotherms of Langmuir films of pure and doped with cholesterol (Ch) amyloid beta, A beta (1-40) and (1-42) at the air-water interface and, scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies of A beta (1-40) and (1-42) layers deposited from solution by drop cast and/or dipping and/or Langmuir-Blodgett on substrates of quartz and Si. The particularity of the substrate surface morphology determines the adhesion forces and plays an important role in the formation and stability of the multilayer films which are deposited on these substrates. The effect of cholesterol on the morphology of amyloids films and appearance of fibril structures is also analysed. AFM investigations have revealed the particularities of the aggregation process of the strongly hydrophobic A beta (1-42) on cholesterol films deposited by Langmuir-Blodgett on solid support of quartz and Si.

We investigate by different complementary methods the processes occurring when a polydimethylsiloxane film is used as interlayer for a silver doped hydroxyapatite coating. The X-ray diffraction and Fourier Transform Infrared Spectroscopy measurements show that the hydroxyapatite doped with silver is in a crystalline form and some SiO44- ions formation takes place at the surface and in the bulk of the new hydroxyapatite doped with silver/polydimethylsiloxane composite layer. The possibility of SiO44- ions incorporation in the structure of silver doped hydroxyapatite by the mechanism of SiO44-/PO43- ions substitution is analysed. The new formed silver doped hydroxyapatite/polydimethylsiloxane composite layer is compact, homogeneous, with no cracks as it was shown by Scanning Electron Microscopy and Glow Discharge Optical Emission Spectrometry.

Radar Cross Section (RCS) is a very important parameter of an aircraft. It is given by the overall signal reflected by the target when it is irradiated by electromagnetic waves in order to be detected and localized. The measurement of RCS for some aircrafts in real scenarios is a very complex and costly process because it needs a certain area for experiments, special equipment and a number of flights. Hence, in most cases the evaluation of RCS is made by measuring a scaled model aircraft in an anechoic chamber. This paper proposes a measurement scenario for IAR 99 and analysis the experimental data. This is the first evaluation of the IAR 99 radar cross section using measurements in time and frequency domain.

We study the generation of p-shell excitons in optically active disk-shaped quantum dots subjected to ultrafast optical pulses. The single-particle spectral properties are obtained from the four-band kp theory, whereas the Coulomb interaction is taken into account within the configuration-interaction approach, particular attention being payed to configuration mixing due to electron-hole correlations. The effect of intraband relaxation processes is included in the non-unitary dynamics derived from the von-Neumann Lindblad equation. We find that the fast hole relaxation processes drive the p-shell excitons to intermediate states which eventually evolve to s-shell excitons via slower electron relaxation.