Formation of Ferroelectric Phases in Sb–S–I Glasses

We have investigated devitrification of glasses within infrared transmitting xSbSI–(100 ? x)Sb₂S₃ pseudo‐binary series, which forms SbSI and Sb₂S₃ ferroelectric crystal phases. Differential scanning calorimetry (DSC) and X‐ray powder diffraction results show unusual behavior for the formation of the SbSI phase, which occurs by two parallel processes: one‐dimensional crystallization at low temperature which starts from the sample surface, and three‐dimensional bulk crystallization that continues the transformation to crystalline state at higher temperatures. The ratio of the intensities of the high‐temperature exothermal peak to the low‐temperature peak in DSC scans increases as the particle size and heating rate are increased. In contrast to the SbSI phase, the temperature of crystallization for the Sb₂S₃ phase does not depend on the particle size. Models are proposed for the origin of the various crystallization mechanisms.     

Development and application of setup for ac magnetic field in neutron scattering experiments

We report on a new setup developed for neutron scattering experiments in periodically alternating magnetic fields at the sample position. The assembly consisting of rf generator, amplifier, wide band transformer, and resonance circuit. It allows to generate homogeneous ac magnetic fields over a volume of a few cm(3) and variable within a wide range of amplitudes and frequencies. The applicability of the device is exemplified by ac polarized neutron reflectometry (PNR): a new method established to probe remagnetization kinetics in soft ferromagnetic films. Test experiments with iron films demonstrate that the ac field within the accessible range of frequencies and amplitudes produces a dramatic effect on the PNR signal. This shows that the relevant ac field parameters generated by the device match well with the scales involved in the remagnetization processes. Other possible applications of the rf unit are briefly discussed.     

Engineering of gold surface work function by electrodeposition of spirobifluorene donor–acceptor bipolar systems

Charge separation in gold/spirobifluorene-based donor (triphenylamine)–acceptor (cyano) bipolar systems has been investigated by contact potential difference and surface photovoltage spectroscopy. Organic films were formed on gold electrode by electrochemical polymerization and by dipping in dye solution. The gold surface work function has been changed over more than 0.4 eV depending on the numbers of electrochemical deposition cycles. Photovoltage effects were analyzed in terms of internal photoemission from Au into organic film, and organic layer light absorption. The energetic differences between the Fermi-level of Au and HOMO levels of organic systems were obtained. The results showed that the electrodeposition is a versatile tool for electrode surface work function tuning.     

New gold and silver-gold catalysts in the shape of sponges and sieves

Gold with a nanoporous sponge-like morphology, generated by leaching of AuAg alloys is presented as a new unsupported material system for catalytic applications. The role of residual silver for catalytic activity towards CO oxidation in the temperature range from −20 to 50°C has been investigated by comparison with Au and Au/Ag zeolite catalysts. As revealed by a systematic variation of the silver content in the zeolite catalysts, bimetallic systems exhibit a significantly higher activity than pure gold, probably due to activation/dissociation of molecular oxygen by silver. By STEM tomography we can unambiguously prove that at least some of the particles form inside the zeolite lattice.