Publications

Using the non-equilibrium Greens' function formalism we calculate the spin currents in a one-dimensional ring coupled to three leads and in the presence of perpendicular magnetic flux (1) and Rashba spin-orbit coupling. A finite bias is applied between the input lead and the other two output leads. We show that the spin-orbit coupling allows one to operate this system as a spin splitter, i.e. the output leads deliver spin-polarized currents with different orientations. We find that the spin splitter operation can be tuned at integer multiples of phi/phi(0). Its efficiency depends not only on the value of the Rashba coupling but also on the bias applied between the input and output leads. The selected spin orientation of the output leads can be reversed by a slight change of their contact position. We discuss as well the connection between the spin splitter operation and the spectral properties of the ring. (C) 2010 Elsevier B.V. All rights reserved.

We report on the development of a modified gas diffusion layer for fuel cells consisting of a simple or teflonized carbon cloth pulsed laser deposited with metal oxide nanostructures designed to operate both as co-catalyst, and oxidic support for other electrochemically active catalysts. We selected TiO2, ZnO and Al2O3 doped (2 wt.%) ZnO which were uniformly distributed over the surface of gas diffusion layers in order to improve the catalytic activity, stability and lifetime, and reduce the production costs of proton exchange membrane fuel cells. We evidenced by scanning electron microscopy and energy dispersive spectroscopy that our depositions consisted of TiO2 nanoparticles while in the case of ZnO and Al2O3 doped (2 wt.%) ZnO transparent quasi-continuous films were synthesized. (C) 2009 Elsevier BM. All rights reserved.

The nonlinear optical (NLO) crystal Y0.7Sc0.3Ca4O(BO3)(3) (starting composition) of good quality has been grown from the melt by the Czochralski pulling method. X-ray diffraction experiments show that the structure of grown crystal belongs to the monoclinic system with space group Cm and its unit cell parameters have been determined to be a = 0.80601(5) nm, b = 1.59946(8) nm, c = 0.35210(7) nm and beta = 101.165(1)degrees. The crystal possesses a wide transmission range from UV to IR, which is advantageous for applications as new NLO material for frequency doubling of solid state lasers operating in the near infrared range.

Two-band superconductivity has a topology different from that in single-band superconductivity. The topology is not always stabilized in an infinitely homogeneous sample. The morphology, grain shape, and pattern of the device (topology of the superconducting materials) is effective in stabilizing the topology. In this report, we discuss a vortex having a small magnetic flux but a large winding number as one plausible topology in a two-band superconductor. (C) 2009 Elsevier B.V. All rights reserved.

Barium magnesium tantalate thin films are attractive materials for high-performance dielectric ceramics for microwave devices, exhibiting a high dielectric constant, a low loss and a near-zero temperature coefficient. We report on the successful deposition of polycrystalline barium magnesium tantalate thin films by RF magnetron sputtering method. The structural and morphological characterization data are presented.

Iron oxide nanoparticles were synthesized in the presence of dextrin. The adsorption process of different dextrin molecules onto the surface of in water dispersed iron-oxide nanoparticles has been investigated to optimize the preparation of iron oxide magnetic fluids. An average iron oxide core size of 8 nm was found by transmission electron microscopy (TEM) for the samples. Scanning electron microscopy (SEM) micro-structural studies revealed a spherical shape of the particles. X-ray phase analysis revealed spinel structure of the iron oxide particles. The attachment of the dextrin on the particle surface was investigated by FTIR spectrometry. The dextrin coated iron oxide nanoparticles were used as targets in Pulsed Laser Deposition (PLD) experiments for thin films synthesis.

A controlled pinning change from the ab-plane dominant to the c-axis dominant has been achieved in a novel method of nanostructured YBa2Cu3Ox (YBCO) growth. The method is a synchronous self-assembly of BaZrO3 (BZO) and Ag-assisted YBCO nanothreads. The formation of entangled nanothreads increases the critical current density while keeping the critical temperature close to that in pure YBCO films. The nanothreads extend through the whole thickness of thick films, making the method suitable for increasing total critical current density per centimeter of width (Ic-w). Two growth mechanisms, the formation of BZO nanorods and YBCO nanocolumns, complement each other, form a coherent structure and produce samples with strong correlated pinning. In addition to the increase in Ic-w, correlated pinning leads to an increase in vortex melting temperature in a wide range of magnetic fields. The films grown by this method have high Ic-w both in low magnetic fields along the c axis and high magnetic fields in the ab plane of YBCO. Such a superconductor would be suitable for both cable and magnet applications.

We report columnar growth of YBa2Cu3Ox (YBCO) films by pulsed laser deposition using nanodots of Au, Ag and Pd deposited on SrTiO3 substrate prior to the growth of the film. The nanodots initiate formation of densely packed YBCO columns with c-axis along the length of the columns. The obtained columnar structure offers enhanced pinning of magnetic flux and provides high critical current density in a magnetic field directed along the c-axis of YBCO while keeping high critical current density for other directions of magnetic field. The evidence of columnar structure is given by the planar and cross-sectional atomic force microscopy, transmissional election microscopy and rotational transport measurements of critical current. By creating the columnar structure, an improvement of critical current up to about 200% is achieved comparable to the reference samples without nanodots in a wide range of magnetic field and thickness of the samples. The largest increase in critical current is observed in magnetic fields close to the matching field calculated from the density of nanoparticles or density of YBCO columns. (C) 2009 Elsevier BM. All rights reserved.

The Pd-TPPTS complex (TPPTS - trisodium salt of 3,3',3 ''-phosphanetriyl benzenesulfonic acid) and PdCl42- salt heterogenised onto Zn2AlNO3 layered double hydroxide (LDH) using an ion-exchange procedure, have been shown to be efficient green catalysts in the cycloisomerisation reaction of acetylenic carboxylic acids to the corresponding 5-membered heterocycles.

We have studied the effect of the morphology on the optical and electrical properties of the TPyP thin films deposited by vacuum evaporation on different substrates (Si with different characteristics, ITO, quartz and glass). The presence of some well-defined B and Q absorption bands has been evidenced. FTIR and photoluminescence measurements have been used to confirm the preservation of the chemical structure of the compound during the evaporation process. The contact Au/TPyP/Si(n) is rectifier, while a blocking behavior has been shown by Si(n)/TPyP/Si(n) and ITO/TPyP/Si(n) and an injector dominated behavior by Si(p)/TPyP/Si(p) and ITO/TPyP/Si(p) heterostructures. The best transmission was obtained on TPyP film deposited on ITO and the highest value of the current in heterostructures Si(n) electrode characterised by a large grain morphology and in consequence by a weak optical and charge carrier scattering at the grain boundaries.