Publications

Second harmonic generation (SHG) investigations on alpha-CN-terthiophene-thiolate-covered GaAs(110) electrodes in 1 N H2SO4 solution revealed significant changes in the rotational anisotropy of the SH response. The enhancement of the 1- and the 3-fold contributions around -250 mV suggests changes in the symmetry properties of the delocalized electron system due to an alteration of the adsorption geometry induced by the applied potentials. The analysis of the EIS data showed that in the potential region where the SH signal exhibits the more important changes the Mott-Schottky plot undergoes a pronounced shift to more negative potentials as a result of the charging of the surface states grouped about 1.06 eV below the conduction band edge. Semiempirical MO calculations suggest that the most energetically favorable interaction implies electron transfer from the semiconductor conduction band to the lowest unoccupied molecular orbital of the organic molecule with epsilon(LUMO) = -1.707 eV. Such a chemisorption bond bringing the organic molecule to a quasi-planar position is well supported by the major changes in the XPS spectra of the electrochemically biased samples with respect to the as-prepared ones. Two distinct N Is species instead of one and a shift of 1.6 eV to higher BE of the terthiophene S 2s core level are strong evidence for a potential-induced change in the adsorption geometry. Taking into account that the acceptor-like surface state group located close to the semiconductor valence edge (E-C,E-S = -1.06 eV) may correspond to the LUMO level (shifted downward by the adsorption process), we assume that the organic molecule, initially adsorbed by the thiolate end, undergoes a conformational change from a tilted to an almost flat position when the applied potential brings the semiconductor Fermi level into its neighborhood. This assumption is in a very good agreement with the potential-induced variation in the thiol thickness estimated from the thiol capacitance.

The corrosion behaviour of carbon steel in 2 M HCl in the presence of N-acetyl p-aminobenzene sulfonamide (APAS) as inhibitor was investigated using weight loss measurements, as well as electrochemical measurements. The morphology of carbon steel surface was investigated using scanning electron microscopy (SEM) and Mossbauer spectrometry. The corrosion current was determined by using Tafel polarization. The inhibition efficiency increased with APAS concentration. The experimental results suggest that the presence of APAS in the solution increases the surface coverage (theta) and therefore, indicate the adsorption of APAS. The adsorption of this compound on the metal surface is found to obey Langmuir's adsorption isotherm. Mossbauer spectroscopy has shown that at this stage the main product of corrosion is a non-stoichiometric amorphous Fe3+ oxyhydroxide, consisting in a mixture of alpha, beta and gamma-FeOOH, where gamma-FeOOH is the main phase.

TiO2 nanopowders, doped with Fe3+ and Eu3+ were obtained by high-energy ball milling and their physical properties were investigated as a function of the doping content and ball milling time. A noticeable red shift and high photoactivity in the degradation and catalytic oxidation reactions of styrene and phenol were found for all doped specimens.

The processes associated with the electrodeposition of thermoelectric Bi(2)(Se,Te)(3) nanowires are reported along with an analysis of the composition, morphology and structure of resulting material. Electrochemical behavior was examined using cyclic and linear voltarnmetry techniques. Energy dispersive X-ray spectrometry (EDX) indicates that the composition of self-standing Bi(2)(Se, Te)(3) wires can be controlled by the electrodeposition method. The composition of Bi(2)(Se,Te)(3) Wires prepared at a potential of -0.01V vs SCE is close to Bi(2)Te(27)Se(0.3). The structure and morphology of Bi(2)(Se,Te)(3) nanowires were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).

In March 2007 the assembly of the Silicon Strip Tracker was completed at the Tracker Integration Facility at CERN. Nearly 15% of the detector was instrumented using cables, fiber optics, power supplies, and electronics intended for the operation at the LHC. A local chiller was used to circulate the coolant for low temperature operation. In order to understand the efficiency and alignment of the strip tracker modules, a cosmic ray trigger was implemented. From March through July 4.5 million triggers were recorded. This period, referred to as the Sector Test, provided practical experience with the operation of the Tracker, especially safety, data acquisition, power, and cooling systems. This paper describes the performance of the strip system during the Sector Test, which consisted of five distinct periods defined by the coolant temperature. Significant emphasis is placed on comparisons between the data and results from Monte Carlo studies.

In order to study the mechanism of the small n-value for Bi2212, E - J characteristics were measured carefully for various kinds of Bi2212 tapes and round wires in high magnetic fields. Some of wires were heat-treated in a magnetic field of 5 T. We found that the n-values of all the samples increase by the in-field heat-treatment at 5 T. In addition, we analyzed the E - J properties by the combination of the percolation model based on the local J(c) distribution and the two directional J(c) distribution model. The improvement of the n-value by the in-field heat treatment can be understood by the change of the aspect-ratio of the grains. Therefore, the aspect-ratio of the grains plays an important role in the current transport influencing not only J(c) but also n-value.

In order to determine the influence of the sintering temperature on the performances of the magnetostrictive materials based sensor for stress, three series of cobalt ferrite (CoFe2O4) samples were prepared by coprecipitation method. These samples were sintered at 1050 degrees C, 1100 degrees C, 1150 degrees C. The spinel structure and the presence of the residual phases were investigated by X-ray diffractometry, scanning electron microscopy and vibrating sample magnetometry. Magnetostrictive properties of the samples were measured by strain gauge technique, in a direction which is parallel to the direction of the applied field. This study was focused on the influence of sintering temperature on magnetic properties and on magnetostriction coefficients. The study reveals that the increase of the sintering temperature increased the magnetostriction coefficients but decreased the strain derivative. Cobalt ferrite obtained by this method can be good candidates for sensors.

We attempted to grow non-c axis heterostructures of substrate-IS type with S = BSCCO and I = (Sr, Ca)CuO(2). A careful selection of the films-substrate relationship is revealed as a key condition toward growth of layered heterostructures with different orientations. However this powerful principle, that is also a mandatory condition, is not sufficient in order to obtain high quality structures. The reasons are discussed looking for further solutions. Our comparative analysis is expanded to other heterostructures we reported in other works trying to reveal some of the more general problems of the non c-axis heterostructures growth.

We study theoretically the electronic transport in parallel few-level quantum dots in the presence of both intradot and interdot long-range Coulomb interaction. Each dot is connected to two leads and the steady-state currents are calculated within the Keldysh formalism using the random-phase approximation for the interacting Green functions. Due to the momentum transfer between the two systems it is possible to get a nonvanishing current through an unbiased Coulomb-blockaded dot, if the other dot is set in the nonlinear transport regime. The transitions between the levels of the passive dot reduce the drag current and lead to negative differential conductance. We also discuss the dependence on temperature and the role of the lead-dot coupling. Copyright (C) EPLA, 2009

Precipitated calcium carbonate as vaterite and small amounts of calcite, with submicron sizes was obtained by a two stages reaction, In the first stage, the limestone was transformed with carbon dioxide in calcium bicarbonate in the absence and the presence of an ultrasonic applied field (35kHz and 0.52 W/cm(2)). The ultrasonic intensity and specific power, the device immersion depth in column suspension and the cavitation was observed to accelerate the dissolving rate of calcium carbonate. In the second stage, the solution of calcium bicarbonate was aerated to obtain calcium carbonate. The experiment was conducted in the absence and the presence of an ultrasonic applied field. The precipitation rate and the calcium carbonate particles size distribution were found to be influenced by the ultrasonic field. The morphology of the crystals formed was unaffected by the ultrasonic field.