Publications

We investigated the temperature (T) variation of the normalized magnetization relaxation rate S and of the corresponding normalized vortex-creep activation energy U* = T/S for YBa2Cu3O7 films containing BaZrO3 nanorods, with the external magnetic field H oriented perpendicular to the film surface. It was found that by increasing the film thickness and using nanodot decorated substrates the high-T S(T) maximum appearing at low H is substituted by a minimum in S(T). As revealed by the analysis of the current density dependence of U*, this behaviour is due to the inhibition of vortex excitations involving double vortex-kinks and superkinks formation in the investigated thick films, owing to the large nanorod splay and pinning energy dispersion.

The electronic and magnetic properties of Ti2CoSi Heusler compound are investigated using density functional calculations. The optimized lattice constant is found to be 6.030 angstrom. The compound is a half-metallic ferromagnet with an energy gap in minority spin channel of 0.652 eV at equilibrium lattice constant, which leads to a 100% spin-polarization. The obtained total magnetic moment from spin-polarized calculations is 3.0 mu(B)for values of lattice constants higher than 5.941 angstrom. The half-metallicity is spoiled for a compressed volume of 4%, suggesting a possible application as pressure sensitive material. (C) 2012 Elsevier B.V All rights reserved.

Laser induced ablation of solids situated in liquids (LAL) was used in order to produce nanoparticles. Laser induced breakdown spectroscopy (LIBS) surface analysis correlated with the process of nanoparticle production by LAL was applied to explain the composition of the obtained nanoparticles as determined by Electron Dispersive X-ray Spectroscopy (EDS). In the case of aluminum rods placed in distilled water irradiated with pulsed laser radiation (355 nm wavelength, 6 ns pulse length) we have obtained spheric nanoparticles with dimensions lower than 100 nm. Quantitative EDS analyses on the obtained spheres showed the presence of, Al, O, and Si. This indicates that probably the composition of the nanoparticles is an aluminum silicate. LIBS analysis on the aluminum target have shown the presence of a Si line with low intensity indicating a small quantity of silicon in the first ablated layers. The LIBS spectra for a sequence of pulses evidenced also that the intensity of the aluminum lines after a number of pulses decreases. This means that the quantity of ablated material becomes smaller due to the ablation depth decrease.

The possibility to do surface measurements on sample containing Eu-151 by detection of Auger electrons delivered in the decay process of the Mossbauer nucleus is briefly presented herein. The test measurements have been carried out on Eu2O3 powder sample. A higher resonance effect and a lower line width have been obtained in backscattering geometry compared with transmission geometry.

The influence of mobile ions on the results of impedance spectroscopy (dielectric spectroscopy) measurements performed on a liquid crystal cell using the new mathematical model recently described was investigated. This mathematical model reformulates the fundamental equation system of continuity for mobile charge carriers and the Poisson equation using new variables. One makes the following assumptions: ions have different mobilities and diffusion coefficients, there is no generation-recombination process, the equilibrium carrier concentrations are uniform and equal each other, the electrodes are either completely blocking or blocked with adsorption-desorption processes. The final result is the analytical expression of the equivalent admittance for the system, allowing to have a clearer picture of the mobile ions and of the processes that occur at the electrode interface influencing the dielectric behavior.

The Bose glass theory for the vortex matter in superconductors with correlated disorder predicts the depinning of vortices due to the renormalization of the vortex pinning barriers by thermal fluctuations. For YB2Cu3O7 (YBCO) in external magnetic fields H oriented along the columnar pins generated by various techniques theoretical estimates give a depinning temperature T (dp) very close to the critical temperature T (c) (T (dp)similar to 0.95T (c)), whereas the results of standard magnetization relaxation experiments are repeatedly interpreted in terms of a much lower T (dp) (similar to 0.5T (c)). We investigated the temperature T variation of the normalized magnetization relaxation rate S for YBCO thin films containing BaZrO3 (BZO) nanorods preferentially oriented along the c axis, with H along the nanorods. The nonmonotonous S(T) variation below the matching field observed up to close to T (c) does not support a low T (dp). The often considered S(T) maximum occurring at relatively low T (which was connected to a disappointing T (dp)) is related to the occurrence of thermomagnetic instabilities. We show that the accommodation of vortices to the columnar pins in the presence of the T dependent macroscopic currents induced in the sample is signaled by a pronounced S(T) deep located at high T, in agreement with a T (dp) close to T (c). By increasing the film thickness and using the substrate decoration the BZO nanorods splay out, leading to the inhibition of (detrimental) vortex excitations involving double vortex kink or superkink formation, characteristic for high-quality thin films and single crystals with columnar pins along the c axis.

Spectrophotometric behavior of riboflavin (RF) adsorbed on silver nanoparticles as well as its interaction with two serum albumins, BSA and HSA, respectively, has been evidenced. The time evolution of the plasmonic features of the complexes formed by RF/BSA/HSA and Ag(0) nanoparticles having an average diameter of 10.0 +/- 2.0 nm have been investigated by UV-Vis absorption spectroscopy. Using steady-state and time-resolved fluorescence spectroscopy, the structure, stability, and dynamics of the serum albumins have been studied. The efficiency of energy transfer process between RF and serum albumins on silver nanoparticles has been estimated. A reaction mechanism of RF with silver nanoparticles is also proposed and the results are discussed with relevance to the involvement of the silver nanoparticles to the redox process of RF and to the RF-serum albumins interaction into a silver nanoparticles complex.

Iron oxide nanoparticles (IONs) coated with different biological (dextran, sucrose) polymers have been synthesized by the coprecipitation method. Biological polymers coated iron oxide nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). Zero field cooled and field cooled magnetizations measurements are also reported. We present a preliminary study of the influence of biological polymer on the interaction effects in powders. The temperature, T (max), of the maximum, increased from 25 K (dextran) to 52 K (sucrose). These values are due to the decrease of interparticle interactions, mainly as a result of the interparticle distance increase.

TiO2-Au aerogels containing different amounts of gold nanoparticles of different sizes (5 and 16 nm) were successfully synthesized using a sol-gel procedure, and were tested for salicylic acid photo-degradation under UV irradiation. The structure and morphology of the obtained materials were investigated using X-ray diffraction, transmission electron microscopy, and N-2 adsorption-desorption measurements. UV-Vis spectroscopy was used to study the optical properties. The effects of the gold nanoparticles on the TiO2 crystallization process were twofold, as follows: (i) the number of crystallized zones was strongly related to the concentration of the gold nanoparticles, and (ii) the smaller gold particles increased the time taken for the crystallization of the samples. It was found that the noble metal-doped samples exhibited higher degradation rates compared with bare titania. It was found that the most active photocatalyst in each studied system was the sample with the highest concentration of gold nanoparticles. Additionally, the highest degradation rate value was obtained with the smallest Au nanoparticles (46.4 x 10(-3) mu mol/(L.s). (C) 2013, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier By. All rights reserved.

We investigated the effect of tritium upload in the dense, polycrystalline MgB2 superconductor for 2 and 216 h. One basic property, the critical temperature T-c, slowly changes in time but is independent of the duration of tritium uptake. Immediately after tritiation, T-c shows a slight increase to 39.1 K but decreases to the critical temperature of the untritiated (pristine) sample, T-c = 38.8 K, after 370 days. The critical current density is strongly dependent on the tritium upload time, mainly at high magnetic fields. The underlying physics is discussed. This behaviour makes the use of MgB2 based conductors advantageous in tritium environments like fusion reactors.