Lewis acid-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control and selective formation of two types of chiral quaternary carbon centers from the single carbon skeleton

The Lewis acid-promoted rearrangement of 2,2,3,3-tetrasubstituted 2,3-epoxy alcohols with several kinds of protecting groups was investigated. When SnCl4 is used as a Lewis acid, the reaction proceeds in a regio- and stereo-controlled manner to afford two types of carbonyl compounds selectively from a single 2,3-epoxy alcohol only by changing the protecting group of the alcohol. The method was then applied to the formation of two types of acyclic and cyclic quaternary carbon centers from the single compound in optically active forms.     

The 4s electron densities of Fe impurity atoms in some transition and noble metals

From internal conversion experiments and the Mössbauer effect measurements, the 4s electron density and isomer shift for Fe impurity atoms in Cr, Ni, Cu, Pt and Au metals were studied. The M and N shell conversion electron spectra of the 14.4 keV transition of⁵⁷Fe were measured using a high resolution β-ray spectrometer and analyzed using a deconvolution methods. The Mössbauer effect measurements were performed by a standard spectrometer with a moving absorber. Most of the samples showed isomer shift values consistent with the published ones. It is concluded that the 4s electron density, \(\rho _{4_S} (0)\) , at the nucleus of⁵⁷Fe embedded is nearly equal in these host metals. The relation between \(\rho _{4_S} (0)\) and the isomer shift indicates that \(\rho _{3_S} (0)\) plays an important role in the variation of the isomer shift.     

Heteroepitaxial growth of gallium nitride on muscovite mica plates by pulsed laser deposition

We have grown GaN films on mica substrates using pulsed laser deposition for the first time and investigated their structural properties using electron beam and X-ray diffraction. We found that GaN (000-1) grows on mica (001) with an in-plane alignment of [11-20] GaN//[010] mica. Despite the large lattice mismatch between GaN and mica, 6 and 43% along the [100] mica and [010] mica directions, respectively, cubic GaN phase or 30° rotated domains are scarcely observed in the film. This phenomenon can be attributed to the enhanced surface migration of film precursors due to the large atomically flat terraces and the weak Van der Waals bonding on the mica surface.     

Displacement-type ferroelectricity with off-center magnetic ions in perovskite Sr(1-x)Ba(x)MnO3

We report a ferroelectric transition driven by the off-centering of magnetic Mn(4+) ions in antiferromagnetic Mott insulators Sr(1-x)Ba(x)MnO(3) with a perovskite structure. As x increases, the perovskite lattice shows the typical soft-mode dynamics, as revealed by the momentum-resolved inelastic x-ray scattering and far-infrared spectroscopy, and the ferroelectricity shows up for x ≥ 0.45. The observed polarization is comparable to that for a prototypical ferroelectric BaTiO(3). We further demonstrate that the magnetic order suppresses the ferroelectric lattice dilation by ～70% and increases the soft-phonon energy by ～50%, indicating the largest magnetoelectric effects yet attained.     

SnCl4-promoted rearrangement of 2,3-epoxy alcohol derivatives: stereochemical control of the reaction

The SnCl₄-promoted rearrangement of 2,2,3,3-tetrasubstituted-2,3-epoxy-1-alcohol derivatives proceeded in a regio- and stereo-controlled manner to selectively give two types of rearranged products from a single isomer by changing the protecting group of the alcohol.     

Enhanced piezoelectric properties of off-stoichiometric strontium bismuth tantalate Sr0.8Bi2.2Ta2O9 ceramics

The piezoelectric properties of strontium bismuth tantalate SrBi₂Ta₂O₉ (SBT) ceramics were enhanced by introducing off-stoichiometry into the starting materials. Sr-deficient and Bi-excess SBT, Sr_0.8Bi_2.2Ta₂O₉ (S_0.8B_2.2T), ceramic samples were prepared by a conventional ceramic technique. The optimum poling conditions (temperature T_p, time t_p, and electric field E_p) were investigated for the piezoelectric measurement. All the obtained independent electromechanical coupling factors of the S_0.8B_2.2T dense ceramics were as follows: k_p=10.6, k₃₁=6.8, k₃₃=14.0, k₁₅=7.8, and k_t=16.2%. The physical constants of the S_0.8B_2.2T ceramics were also determined. The piezoelectric constants were d₃₃=13.0, d₃₁=6.0, and d₁₅=10.2 pC/N. PACS 77.84.Dy; 61.66.Fn; 77.65.-j     

Performance Characteristics of Power Build-Up Cavity for Raman Spectroscopic Measurement

Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼10300 achieved a stable TEM₀₀ mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/− 0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.     

Boron-substituted difluorocyclopropanes: new building blocks of gem-difluorocyclopropanes

Cycloaddition of difluorocarbene to alkenyl boronates 3 gave boron-substituted gem-difluorocyclopropanes 2 in stereospecific fashion. Upon treatment with lithium carbenoids, cyclopropyl boronates 2 underwent one-carbon homologation to afford a variety of gem-difluorocyclopropanes in good yields.     

Growth of InN films on spinel substrates by pulsed laser deposition

We have grown InN films on MgAl₂O₄(111) substrates with atomically flat surfaces using pulsed laser deposition (PLD) and compared their structural properties with those grown on (Mn,Zn)Fe₂O₄(111) substrates. It has been revealed that InN(0001) films grow on MgAl₂O₄(111) with an in‐plane epitaxial relationship of InN[1 00] // MgAl₂O₄[1 0], achieving a lattice mismatch minimum. The InN films exhibited a clear sixfold rotational symmetry, without 30° rotational domains and with a full width at half maximum value of the InN 0002 rocking curve being 17.5 arcmin. Comparison between InN films grown on MgAl₂O₄ and those on (Mn,Zn)Fe₂O₄ led us to conclude that suppression of the interfacial reactions between the InN films and the substrate is inherently important to obtain high quality InN on substrates with a spinel structure. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)