Stress dependence on N/Ga ratio in GaN epitaxial films grown on ZnO substrates

GaN films were grown on ZnO substrate under various beam equivalent pressure ratios by plasma-assisted molecular beam epitaxy (P-MBE). We theoretically calculated the thermal stress caused by the difference of thermal expansion coefficients between GaN and ZnO. The changes of stress and critical thickness were evaluated by measurement of XRD for HT GaN and LT GaN buffer grown under Ga-rich and N-rich conditions. From this study, we observed that GaN grown under Ga-rich condition causes GaN film to under compressive-stress, while GaN grown under N-rich condition was tensile-stressed. Consequently, interdiffusion has no effect on the variation of the critical thickness.     

Theoretical Study of the Electronic Excited States and Fluorescence Spectra of Squaraine in Solution

Bis[4-(dimethylamino)phenyl]squaraine (SQ-DMA) has been used as a long wavelength fluorescence dye. In spite of various experimental and theoretical studies, its excited state properties and the relaxation mechanism have not been elucidated. In this work, we tried to clarify these points from a theoretical point of view. The heats of reaction from the planar to possible twisted conformers in the first excited state S₁ in solvents were calculated to be significantly endothermic, thus the twisted structures turn out to be less important, which contradicts earlier proposals made in experimental studies. This behavior is in a sharp contrast with that of the related molecule 4-(N,N-dimethylamino)benzonitrile, and is explained by the difference in their electronic characters of their relevant excited states; the S₁ state of SQ-DMA is a simple HOMO-to-LUMO excited state with a delocalized character. Furthermore, the theoretically simulated absorption and fluorescence spectra with the planar structure of SQ-DMA are in good agreement with the corresponding experimental results. These results suggest that the responsible S₁ state is the lowest ¹B_1u state with a planar D_2h structure.     

Determination of acid dissociation constants of flavin analogues by capillary zone electrophoresis

Acid dissociation constants (pK_a) of nine kinds of flavin analogues as molecular catalyst candidates were determined by CZE. Although some of the analogues are instable and degradable under the light exposure or in alkaline aqueous solutions, the effective electrophoretic mobility of the flavin analogue of interest has been measured with the residual substance. The pK_a values of the flavin analogues were analyzed through the changes in the effective electrophoretic mobility with varying pH of the separation buffer. One or two steps pK_a values were determined by the analysis. One of the degraded species from the flavin analogues, lumichrome, was also detected in the CZE analysis, and its pK_a values were also determined. While coexisting impurities generated over the storage conditions were found in some analogues, the pK_a values of the target analogues were successfully determined with the help of the CZE separations. A pressure-assisted CZE was utilized for the determination or the estimation of the pK_a values of such analogues as possessing carboxylic acid moiety.     

Cyclophane with eclipsed pyrene units enables construction of spin interfaces with chemical accuracy

Advanced functionality in molecular electronics and spintronics is orchestrated by exact molecular arrangements at metal surfaces, but the strategies for constructing such arrangements remain limited. Here, we report the synthesis and surface hybridization of a cyclophane that comprises two pyrene groups fastened together by two ferrocene pillars. Crystallographic structure analysis revealed pyrene planes separated by ∼352 pm and stacked in an eclipsed geometry that approximates the rare configuration of AA-stacked bilayer graphene. We deposited this cyclophane onto surfaces of Cu(111) and Co(111) at submonolayer coverage and studied the resulting hybrid entities with scanning tunnelling microscopy (STM). We found distinct characteristics of this cyclophane on each metal surface: on non-magnetic Cu(111), physisorption occurred and the two pyrene groups remained electronically coupled to each other; on ferromagnetic Co(111) nanoislands, chemisorption occurred and the two pyrene groups became electronically decoupled. Spin-polarized STM measurements revealed that the ferrocene groups had spin polarization opposite to that of the surrounding Co metal, while the pyrene stack had no spin polarization. Comparisons to the non-stacked analogue comprising only one pyrene group bolster our interpretation of the cyclophane''s STM features. The design strategy presented herein can be extended to realize versatile, three-dimensional platforms in single-molecule electronics and spintronics.

A chemical strategy for the bottom-up construction of 3D spin interfaces is presented. Scanning tunnelling microscopy reveals distinct electronic features of a cyclophane with precisely designed pi-stacking on ferromagnetic Co(111) nanoislands.     

Generation of an intense low-velocity metastable-neon atomic beam

A metastable neon (1S ₅) atomic beam with a velocity of 394 m/s (373 K) and an intensity of 1.1×10¹⁵ s^–1 sr^–1 is produced with a novel construction using a dc glow discharge.     

Total synthesis of (±)-kainic acid: a photochemical C-H carbamoylation approach

A novel photochemical C-H carbamoylation of an octahydroisoindole derivative with PhNCO has allowed the authors to provide a unique access to a highly functionalized proline motif from which total synthesis of (±)-kainic acid, a bioactive marine alkaloid, has been accomplished.     

Nonlinear normal modes and primary resonance of horizontally supported Jeffcott rotor

The nonlinear normal modes of a horizontally supported Jeffcott rotor are investigated. In contrast with a vertically supported rotor, there are localized and nonlocalized nonlinear normal modes because the linear natural frequencies in the horizontal and vertical directions are slightly different due to both gravity and the nonlinearity of restoring force. Reflecting such nonlinear normal modes, the frequency response curves are characterized in the primary resonance. In the case where the eccentricity is small, i.e., the response amplitude is small, the whirling motion is localized in the horizontal or vertical direction in the resonance. On the other hand, when the eccentricity is large, two kinds of whirling motion, which are localized in the vertical direction and nonlocalized in any direction, coexist simultaneously in a region of rotational speed. Experiments are conducted, and the theoretically predicted nonlinear responses based on localized and nonlocalized nonlinear normal modes are observed.     

Generators and Dimensions of Derived Categories of Modules

Several years ago, Bondal, Rouquier, and Van den Bergh introduced the notion of the dimension of a triangulated category, and Rouquier proved that the bounded derived category of coherent sheaves on a separated scheme of finite type over a perfect field has finite dimension. In this article, we study the dimension of the bounded derived category of finitely generated modules over a commutative Noetherian ring. The main result of this article asserts that it is finite over a complete local ring containing a field with perfect residue field. Our methods also give a ring-theoretic proof of the affine case of Rouquier's theorem.     

Synthesis,Structure, and Complexation of an S-Shaped Double Azahelicene with Inner-Edge Nitrogen Atoms

An S-shaped double azahelicene ( 1 ) was synthesized in excellent yield by a palladium-catalyzed double dehydrogenative C−H coupling reaction. The stereochemistry of 1 was confirmed to be dl by single-crystal X-ray diffraction analysis. Selective formation of dl- 1 was attributed to the isomerization of the kinetically controlled product (meso- 1 ) into the more thermodynamically stable dl- 1 under the applied reaction conditions. dl- 1 can coordinate to palladium(II) in a bidentate trans-chelating fashion, which was confirmed by X-ray absorption fine structure (XAFS) as well as by X-ray photoelectron spectroscopy (XPS), diffuse reflectance (DR) UV/Vis, and far-infrared (FIR) absorption spectroscopy. Theoretical calculations of palladium complex 16 revealed a weak attractive interaction between palladium and carbon atoms on the central dimethoxynaphthalene core, which could facilitate a disproportionation between a trans-chelating (dl- 1 ) ⋅ PdCl₂ complex and PdCl₂ to form 16 .     

Highly Enhanced Emission of Visible Light from Core–Dual‐Shell‐Type Hybridized Nanoparticles

Core–dual‐shell‐type hybridized nanoparticles (NPs) having Au‐core/dye‐doped silica inner shell/Au outer shell are successfully fabricated by developing a biphasic process that is a kind of so‐called “one‐pot” method. The resulting hybridized NPs exhibit evidently about 20‐fold enhancement of fluorescence intensity, increase in fluorescence quantum yield, and decrease in fluorescence lifetime. These effects depend on the metal nanostructure being optimized, compared with the reference hybridized NPs with neither a Au‐core nor a Au outer shell, due to the gap‐mode effect induced by localized surface plasmon resonance in the core–dual‐shell‐type MIM‐like nanostructure. More detailed elucidation concerning the enhancement mechanism will provide the possibility of photonic device application, for example as a high‐performance point light source, nanolaser, or sensor for bioimaging in the visible region in the near future.