National Institute Of Materials Physics - Romania

Widely applicable nonaqueous solution routes have been employed for the syntheses of crystalline nanostructured tungsten oxide particles from a tungsten hexachloride precursor. Here, a systematic study on the crystallization and assembly behavior of tungsten oxide products made by using the bioligand deferoxamine mesylate (DFOM) (product I), the two chelating ligands hexadecyltrimethylammoniumbromide (CTAB) (II) and poly(alkylene oxide) block copolymer (Pluronic P123) (III) is presented. The mechanistic pathways for the material synthesis are also discussed in detail. The tungsten oxide nanomaterials and reaction solutions are characterized by Fourier transform IR, H-1, and C-13 NMR spectroscopies, powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, and selected-area electron diffraction. The indexing of the line pattern suggests WO3 is in its monoclinic structure with a=0.7297nm, b=0.7539nm, c=0.7688nm, and beta=90.91 degrees. The nanoparticles formed have various architectures, such as chromosomal shapes (product I) and slates (II), which are quite different from the mesoporous one (III) that has internal pores or mesopores ranging from 5 to 15 nm. The nanoparticles obtained from all the synthetic procedures are in the range of 40-60 nm. The investigation of the gas-sensing properties of these materials indicate that all the sensors have good baseline stability and the sensors fabricated from material III present very different response kinetics and different CO detection properties. The possibility of adjusting the morphology and by that tuning the gas-sensing properties makes the preparation strategies used interesting candidates for fabricating gas-sensing materials.

The leakage current in epitaxial BiFeO3 capacitors with bottom SrRuO3 and top Pt electrodes, grown by pulsed laser deposition on SrTiO3 (100), SrTiO3 (110), and SrTiO3 (111) substrates, is investigated by current-voltage (I-V) measurements in the 100-300 K temperature range. It is found that the leakage current is interface-limited and strongly dependent on the orientation of the substrate. The potential barriers at the electrode interfaces are estimated to about 0.6, 0.77, and 0.93 eV for the (100), (110), and (111) orientations, respectively.

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.