Publications

In a planar oriented sample of a calamitic nematic lyotropic system ( mixture of sodium lauryl sulphate/water/decanol), isotropic pretransitional domains appear at the nematic to isotropic transition. The domains are oblong in shape with the long axis along the orientational direction. We show experimental evidence that this oblong shape is determined by the nematic-isotropic interfacial tension anisotropy. Two uniparametric models of simple angular dependences for the interfacial tension are tested. Using the differential system obtained from the Young-Laplace condition at the nematic-isotropic interface, the domain shape can be numerically calculated for each value of the interfacial tension anisotropy. By processing the values of the transmitted light through both an isolated isotropic domain and its surrounding nematic zone, we obtain the anisotropy of the interfacial tension as the main fitting parameter. An estimation of the ratio of the extreme values for the interfacial tension is given.

(Cu, C)Ba2Ca3Cu4Ox superconductor with addition of y mol LiF has been synthesized by a high-pressure method. For the same synthesis conditions it was found that (almost) single-phase Cu, C-1234 samples can be synthesized for y(LiF) = 0-0.1 if the amount of z mol AgO oxidizer is increased linearly from Z(AgO) = 0.45 to 0.73 and for y(LiF) = 0 - 1-0.2 if ZAgO = 0.73 = constant. Transport measurements (rho(T) and room-temperature Seebeck coefficient) have shown that these samples are overdoped: LiF is an effective addition for synthesis of overdoped Cu, C-1234 with a controlled level of carriers. LiF addition continuously decreases T-c. The critical point at y(LiF) = 0.1 is discussed as the solubility limit of LiF and/or the point where the doping mechanism changes. It is proposed that the reason is the reaction of extra Li with C and O to form Li2CO3, inducing a lower concentration of C in Cu, C-1234/LiF crystals, and at the same time a possible substitution of Li not only for the Cu site but also for the Ca site, resulting in formation of a higher amount of residual Ca0.828CuO2 (for y(LiF) > 0.1). LiF induces the formation of a liquid phase and acts as a flux promoting the formation of Cu, C-12(n - 1)n with n greater than or equal to 4. LiF modifies to some degree the grain growth from a 3D to a 2D type (thinner platelike grains have been observed in the LiF added samples).

The principal of a semiconductor particle detector is briefly outlined and applications in several fields of fundamental and applied physics mentioned. Starting from the basic physics motivation in High Energy Physics (HEP) research, the further discussion then focuses on the use of these devices in present and future HEP experiments outlining especially the requirements for precise measurements of elementary particle tracks, a task ideally fulfilled by segmented silicon detectors. These developments have also initiated further applications in different fields as e.g. material analysis, medical imaging and space missions. In future HEP-experiments such devices will however face an unprecedented challenge imposed by extremely intense radiation fields. Basics of hadron and lepton induced radiation damage in silicon are described together with their implications on the detector quality. The following part of the report is then dealing with several approaches to improve the radiation tolerance of silicon detectors. Defect engineering of the semiconductor material, modified detector geometries and specific operational conditions are outlined. First results toward a complete understanding of detector degradation as caused by point and cluster defects are given and these promising successes may finally pave the way for developments of superior devices.

The complex structure fullerene(C-60)-nanotubule has been built from special plastic units and relaxed by a computer Monte-Carlo - Metropolis procedure. The purpose was to show that interconnection fullerene-nanotubule is possible from the energetical point of view. The results open the way towards the assessing the possibility to create nano-conductors and connections between different parts of nano-devices, using nano-carbon configurations filled by metal atoms.

CdTe nanowires were electrodeposited in ion track membranes with pore diameters in the range 100-2000 nm. Acidic and basic baths were tested for obtaining materials with good stoichiometry. The cyclic voltammograms were compared for the case of deposition on a carbon rotating disc and on the porous membrane substrates, the differences being attributed to the additional resistance induced by the pores. For larger pores a tendency of growing hollow structures was observed.

Samples of FC3-xMnxO4 (x=0-0.6) were studied below the Verwey transition (T=122, 77, and 4.2 K) by Fe-57 Mossbauer spectroscopy. Considering that Mn2+ substitutes for Fe2+ on octahedral sites, we inferred the existence of five subspectra at all temperatures, one for Fe3+ ions on tetrahedral sites, two for Fe3+ ions on octahedral sites, and two for Fe2+ ions on octahedral sites. The hyperfine magnetic fields of one Fe3+ sublattice and two Fe2+ sublattices decrease slightly with increasing the amount x of Mn substitutions. The results are consistent with the existence of localized octahedral Fe3+ and Fe2+ spin states below the Verwey temperature. (C) 2003 Elsevier B.V. All rights reserved.

The influence of disorder and interaction effects on the ground state polarization of the two-dimensional correlated electron gas is studied by numerical investigations of the unrestricted Hartree-Fock approach. With the model of Anderson disorder a continuous increase of the spin magnetization until the fully polarized regime is obtained. The ferromagnetic ground state is found to be favorable when the electron number is lowered and the interaction and disorder parameters are suitably chosen.

Optical bireffingence measurements for a calamitic lyotropic liquid crystal containing sodium lauryl sulphate/decanol/water are presented. A value of the order of 10(-3) was obtained, much smaller than that of thermotropic liquid crystals. The order parameter temperature dependence is evaluated using an extrapolating method and taking into accounts the influence of the micelle shape. (C) 2004 WILEY-VCR Verlag GmbH & Co. KGaA, Weinheim.

Substituted ferrites with the chemical composition MxFe1-xFe2O4-nH(2)O (M: Mn(II), x: 0.35, n: 0.4; M: Ni(II), x: 0.38, n: 1; M: Zn(II), x: 0.45, n: 0.35) have been prepared by a soft chemical method using as starting materials magnetite and suitable acetates. These compounds have been characterised by elemental chemical analysis, thermal analysis, IR spectroscopy, X-ray diffraction on powder, transmission electron microscopy studies as well as Mossbauer spectroscopy and magnetic measurements at room temperature. The X-ray diffraction study indicates that the substituted ferrites adopt a cubic structure and the size of particles determined from the diffraction peak is fairly close to that indicated for agglomerates by transmission electron microscopy. The magnetic methods agree to the substitution of Fe(II) in the octahedral positions preserving the inversed spinel structure. (C) 2003 Elsevier B.V. All rights reserved.

Critical current density J(c) of Na0.35CoO2.1.3H(2)O superconductor (T-c=4.4 K) has been estimated from magnetization measurements: J(c)(1.9 K,0 T)=5x10(4) A/cm(2), J(c) (1.9 K,0.4 T)=4x10(2) A/cm(2) and J(c) (3.4 K,0 T)=10(3) A/cm(2). J(c) versus applied magnetic field H cannot be fitted, as for high-T-c superconductors (HTS), by a power law for any temperature. The temperature dependence for a given H is not of the linear type as for MgB2, but is close to quasiexponential (associated with the thermally activated flux creep) as for HTS. Irreversibility field data points H-irr versus (1-T/T-c) obey a power law with power exponent n=3.4. The irreversibility line is located below, but in vicinity of, the line for Bi-2223. Details of morphology are also presented. (C) 2004 American Institute of Physics.