Publications

The atomic structure of dislocations in cubic boron nitride has been investigated by high resolution transmission electron microscopy. Most of the perfect dislocations, screw and 60degrees edge, are dissociated. A 60degrees dislocation which was undissociated has been analysed. Computer simulation is performed in an attempt to characterise the core structure. Twinning dislocations and dislocations resulting from the intersection of stacking faults are also revealed. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

New magnetic composite materials, ribbon samples, with nominal compositions FexCu1-x (x=0.2; 0.5; 0.8) were obtained by the melt spinning technique. Various information was provided via X-ray diffraction, Mossbauer and magnetic measurements. The structural aspects: phase composition, size and texture effects, have been corroborated with magnetic properties. Finally, the possibility to choose the adequate composition and the suitable processing in order to obtain desired anisotropic magnetic materials were presented.

Selenium-sulphur layers prepared by warm pressing or deposited by pulsed laser deposition (PLD) on silicon wafers were subjected to laser pulses in order to test the possibility of recording the optical information in these glassy materials. There was demonstrated that the contrast of reflectivity between the irradiated places and the amorphous matrix could be used for storage of information at a reasonable density.

The crystalline structure, the interlayer and the epitaxial growth stage of PZT/IrO2 deposited by sol-gel method, were investigated using: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) (in bright field (BFTEM) and in dark field (DFTEM)), in correlation with selected area electron diffraction (SAED), high resolution electron microscopy (HRTEM) and X-ray energy dispersive spectroscopy (EDS). On the IrO2 electrodes, preferential (110) orientation was obtained. The crystalline growth of PZT film depends on the initial state of surface at the initial moment and on the relationship between PZT and bottom electrode IrO2. In particular, the interlayer Ir3Ti, formed between PZT and IrO2 plays an important role in the epitaxial growth of PZT film.

We have investigated the effect of Li2CO3 addition on the transport and magnetic properties of Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox, samples in connection with the structural changes observed by scanning electronic microscopy (SEM) and X-ray diffraction. In addition to the results reported in literature, we have extracted new information from the magnetic hysteresis loops and AC susceptibility measurements. One such information is the splitting of the AC loss peak corresponding to the dissipation inside the Bi-2223 grains. The results reported here have been compared with those obtained for Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiF)(y) and Bi1.7Pb0.4Sr1.5Ca2.5Cu3.6Ox/(LiCl)(y) specimens, and the effect of halogen is pointed out. (C) 2004 Elsevier B.V. All rights reserved.

Cubic boron nitride (c-BN) crystalline superabrasive powder (Borazon** CBN 400), consisting of 200-300 microns sized amber colored crystallites prepared by HP/HT synthesis, has been examined from 2.1 K to 293 K by X-band ESR spectroscopy. The observed spectrum consists of a component line A1, visible in the whole temperature range, and two component lines A2 and A3, visible at high and low temperatures, respectively. The A1 and A3 lines originate from transitions inside S = 1/2 ground states of distinct paramagnetic species and A2 from transitions inside an excited state of another paramagnetic center. The intensity of the A1 and A3 lines changes differently during in situ low temperature illumination in the UV-VIS range. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Triglycine sulfate crystals (TGS) doped With L- and D-alanine, respectively, where grown in paraelectric phase at 52 degreesC. They show stable parameters versus pure TGS crystals, lower permittivities and losses, i.e. higher pyroelectric figure of merit. L- and D-alanine-doped crystals show a mirror asymmetry of the growth habit along the ferroelectric axis. Hysteresis loop of pure and doped samples were automatically recorded. Internal bias field of about I kV/cm, induced by the two dopants, stabilizes the polarization components P+ and P- in opposite directions. Spontaneous polarization of doped crystals shows two unequal P+/P- components, having a peculiar dependence on the ac applied electric field. Dopage simulation of pure TGS samples, using several bias fields, shows even more complicated pattern. Pyroelectric coefficients were evaluated from pyroelectric current measurements. A remarkable asymmetry of the pyroelectric coefficient peak values for the enantiomorphous-doped crystals was noticed, crossing up and down the Curie point. This fact suggests a non-equivalent L/D-alanine dopant substitution of the glycine group GI in the host lattice. It has been shown that the pyroelectric coefficient can be increased at room temperature, under an optimized dc electric field applied on the pyroelectric wafer. Doped crystals are suitable for IR detector and for more stable gas sensors applications in pollution monitoring. (C) 2004 Elsevier B.V. All rights reserved.

We have used scanning Hall probe microscopy to correlate vortex images and local magnetisation measurements in two different high temperature superconducting samples. Near the edge of a continuous YBCO thin film we have observed local hysteresis inversion and negative remanent fields, which can be semi-quantitatively explained in terms of a theoretical model of flux penetration in an infinitely long superconducting strip. In a YBCO film containing a regular square array of antidots we have further find that vortices trapped at antidots exhibit an unusual behaviour upon field sweep reversal. (C) 2004 Elsevier B.V. All rights reserved.

We study the transport properties of coherently coupled quantum dots in the quantum Hall regime within the Landauer-Buttiker formalism which captures and explains the experimentally observed features in terms of the spectral properties of the coupled dot system. The subpeak structure of the transmittance spectrum and the charging stability diagrams are obtained and discussed. The role of the intradot and interdot Coulomb interaction are pointed out. We show the subpeak evolution with the magnetic field and predict a specific oscillatory behavior of the Hall resistance in strong magnetic field which can be experimentally tested.

The third harmonics of the ac susceptibility chi(3) of MgB2 bulk samples have been measured in the frequency range 61-1070 Hz as a function of the temperature for different applied dc magnetic fields. The irreversibility line (T-irr versus H-dc) deduced from the temperature onsets of chi(3) for each field shows a frequency dependence: The onset temperature increases as the frequency increases. This frequency dependence has been analyzed using the 3D vortex-glass model. Moreover the real versus imaginary components of the chi(3) for each dc magnetic field have been interpreted with a 3D glass creep using a numerical analysis based on a non-linear diffusion equation of the magnetic field. (C) 2004 Elsevier B.V. All rights reserved.