Three‐Dimensional,Time‐Resolved Profiling of Ferroelectric Domain Wall Dynamics by Spectral‐Domain Optical Coherence Tomography

We apply here spectral‐domain optical coherence tomography (SD‐OCT) for the precise detection and temporal tracking of ferroelectric domain walls (DWs) in magnesium‐doped periodically poled lithium niobate (Mg:PPLN). We reproducibly map static DWs at an axial (depth) resolution down to ～ 0.6 μm, being located up to 0.5 mm well inside the single crystalline Mg:PPLN sample. We show that a full 3‐dimensional (3D) reconstruction of the DW geometry is possible from the collected data, when applying a special algorithm that accounts for the nonlinear optical dispersion of the material. Our OCT investigation provides valuable reference information on the DWs’ polarization charge distribution, which is known to be the key to the electrical conductivity of ferroelectric DWs in such systems. Hence, we carefully analyze the SD‐OCT signal dependence both when varying the direction of incident polarization, and when applying electrical fields along the polar axis. Surprisingly, the large backreflection intensities recorded under extraordinary polarization are not affected by any electrical field, at least for field strengths below the switching threshold, while no significant signals above noise floor are detected under ordinary polarization. Finally, we employed the high‐speed SD‐OCT setup for the real‐time DW tracking upon ferroelectric domain switching under high external fields.     

Control of dark current in photoelectrochemical (TiO2/I--I3-)) and dye-sensitized solar cells

The ruthenium complex bis-tetrabutylammonium cis-dithiocyanato-N,N'-bis-2,2'-bipyridine-4-carboxylic acid, 4'-carboxylate ruthenium(II), N-719, was found to block the dark current of dye sensitized solar cells (DSC), based on mesoporous TiO2 films deposited on a F-doped tin oxide electrode and the effect was compared to surface treatment by TiCl4 and the introduction of a compact TiO2 blocking layer.     

Regiocontrolled Ru-catalyzed addition of carboxylic acids to alkynes: practical protocols for the synthesis of vinyl esters

The catalytic activity of commercially available, air and water stable ruthenium complexes in the addition of carboxylic acids to terminal alkynes was found to be drastically enhanced by the addition of small quantities of base. Moreover, the regioselectivity of the reaction can be controlled by the choice of the base so that both the Markovnikov (Na2CO3) and the anti-Markovnikov products (DMAP) are now easily accessible in excellent selectivities.     

Siegel discs, Herman rings and the Arnold family

We show that the rotation number of an analytically linearizable element of the Arnold family , , , satisfies the Brjuno condition. Conversely, for every Brjuno rotation number there exists an analytically linearizable element of the Arnold family. Along the way we prove the necessity of the Brjuno condition for linearizability of and , , at 0. We also investigate the complex Arnold family and classify its possible Fatou components. Finally, we show that the Siegel discs of and are quasidiscs with a critical point on the boundary if the rotation number is of constant type.

     

Analyticity and uniqueness of the invariant equilibrium states for general spin 1/2 classical lattice systems

Asano-Ruelle-Slawny method is generalized to discuss analyticity and uniqueness of the correlation functions in terms of the group structure associated with any lattice systems. The use of Poisson formula for abelian groups gives a simple method to obtain explicit domains where the above properties are verified.     

Hartree-Fock interaction between a helium atom and lithium metal: A test for the effective medium theory

The interaction of a helium atom with 6 and 10 atom clusters of lithium has been calculated using the unrestricted Hartree-Fock method, Hartree-Fock method with correlation corrections, and the effective medium theory. Inside the cluster the helium embedding energy is found to be proportional to the electron density of the cluster. The proportionality constant obtained by the Hartree-Fock method is in fair agreement with that calculated in the homogeneous electron gas using the local density approximation. Outside the cluster, in the region compatible with the helium diffraction experiments, the self-consistent calculations give much larger repulsion than the effective medium theory.