Laser-sintered mesoporous TiO2 electrodes for dye-sensitized solar cells

Low-temperature laser sintering has been successfully demonstrated to improve the overall conversion efficiency of dye-sensitized solar cells. Mesoporous TiO₂ electrodes were prepared from a colloidal solution of TiO₂ nanopowders by a laser direct-write technique and then sintered by a quasi-continuous-wave UV laser (λ=355 nm) for the fabrication of dye-sensitized solar cells. The overall conversion efficiency of the cells based on the laser-sintered TiO₂ electrodes was double that of the devices with non-laser-treated TiO₂ electrodes. This enhancement is attributed to both the removal of organic additives and the improved inter-nanoparticle electrical contacts induced by the laser-sintering process, which led to an increase in porosity and dye-absorption sites in the TiO₂ electrodes. PACS 61.80.Ba; 61.46.+w; 73.22.-f; 84.60.Jt     

High-frequency characteristics of CoFeVAlONb thin films

High-frequency characteristics of CoFeVAlONb thin films were studied. A thin film of Co_43.47Fe_35.30V_1.54Al_5.55O_9.93Nb_4.21 is observed to exhibit excellent magnetic properties; magnetic coercivity of 1.24 Oe, uniaxial in-plane anisotropy field of 66.99 Oe, and saturation magnetization of 19.8 kG. The effective permeability of the film is as high as 1089 and is stable up to 1.8 GHz, and with ferromagnetic resonance over 3 GHz. This film also has very high electrical resistivity of about 628 μΩ cm. These superior properties make it ideal for high-frequency magnetic applications.     

Calorimetric studies of the growth of Desulfovibrio desulfuricans in the presence of nitrocellulose

Calorimetric results indicate that nitrocellulose (NC)-induced changes in the metabolism of Desulfovibrio desulfuricans 1388 are caused by both chemical (nitrate) and physical (biofilm formation) factors. Nitrate added to lactate-based culture medium with nitrocellulose competed for the electron flux from lactate and suppressed the bacterial sulfidogenesis and growth. The presence of an insoluble compound (carbon backbone of the polymer) induced the creation of a biofilm-like structure with its own metabolism.     

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

Rare earths exhibit complex magnetic phase diagrams resulting from the competition between various contributions to the magnetic energy: exchange, anisotropy and magnetostriction. The epitaxy of a rare-earth film on a substrate induces (i) a clamping to the substrate and (ii) pseudomorphic strains. Both these effects are shown to lead to modifications of the magnetic properties in (0 0 1)Dy, (0 0 1)Tb and (1 1 0)Eu films. In Dy and Tb films, spectacular variations of the Curie temperature have been evidenced. Additionally, Tb films exhibit a new large wavelength magnetic modulation. In Eu films, one of the helical magnetic domains disappears at low temperature whereas the propagation vectors of the other helices are tilted. The link between structural and magnetic properties is underlined via magnetoelastic models. Moreover, molecular beam epitaxy permits the growth of Sm in a metastable dhcp phase. The magnetic structure of dhcp Sm has been elucidated for the first time. In this review, neutron scattering is shown to be a powerful technique to reveal the magnetic structures of rare-earth films.     

Electro-optic pulse response of ferroelectric liquid crystals

The electro-optic response of ferroelectric smectic C* liquid crystals has been studied. Anomalous switching behaviour of such materials which possess a negative dielectric anisotropy has been reported. These materials show a minimum in response time at a sufficiently high field. We present results showing the dependency of this minimum upon spontaneous polarisation and the effect of AC bias. Calculations based upon the equation of motion of the director around the cone are presented which describe this effect and its dependence on the relative magnitudes of the spontaneous polarization and dielectric anisotropy of the material. Good agreement with the experimental results is found.     

Thermal desorption of interacting molecules from mixed adlayers

A Monte Carlo simulation method is used to study thermal desorption of gas molecules from mixed adlayers containing two species. The effects of lateral interactions among adatoms and initial surface coverage on the desorption spectra are examined. It is shown that attractive lateral interactions lead to sharper peaks and that desorption occurs at high temperatures, whereas repulsive interactions lead to multiple peak spectra. It is found that interactions between unlike molecules affect the spectra for species with lower desorption energy only, and that the two species desorb together only in certain cases. Lateral interactions also affect the desorption kinetics significantly and very different behavior for the two species may be obtained.     

Three-body problem in the theory of the dielectric constant

We study the corrections to the Clausius-Mossotti formula for the dielectric constant of a disordered system of polarizable spherical particles. Previously we have derived an exact cluster expansion for the correction terms. Here we study the three-body correction in detail. We derive an explicit expression for the integrand of the three-body cluster integral for a system of polarizable point dipoles.