Responsive Four-Coordinate Iron(II) Nodes in FePd(CN)4

Metal node design is crucial for obtaining structurally diverse coordination polymers (CPs) and metal–organic frameworks with desirable properties; however, Fe^II ions are exclusively six-coordinated. Herein, we present a cyanide-bridged three-dimensional (3D) CP, FePd(CN)₄, bearing four-coordinate Fe^II ions, which is synthesized by thermal treatment of a two-dimensional (2D) six-coordinate Fe^II CP, Fe(H₂O)₂Pd(CN)₄⋅4 H₂O, to remove water molecules. Atomic-resolution transmission electron microscopy and powder X-ray and neutron diffraction measurements revealed that the FePd(CN)₄ structure is composed of a two-fold interpenetrated PtS topology network, where the Fe^II center demonstrates an intermediate geometry between tetrahedral and square-planar coordination. This four-coordinate Fe^II center with the distorted geometry can act as a thermo-responsive flexible node in the PtS network.     

Spontaneous formation of wurzite-CdS/zinc blende-CdTe heterodimers through a partial anion exchange reaction

Ion exchange of ionic semiconductor nanoparticles (NPs) is a facile method for the synthesis of type-II semiconductor heterostructured NPs with staggered alignment of band edges for photoelectric applications. Through consideration of the crystallographic orientation and strain at the heterointerface, well-designed heterostructures can be constructed through ion exchange reactions. Here we report the selective synthesis of anisotropically phase-segregated cadmium sulfide (CdS)/ cadmium telluride (CdTe) heterodimers via a novel anion exchange reaction of CdS NPs with an organic telluride precursor. The wurtzite-CdS/zinc blende-CdTe heterodimers in this study resulted from spontaneous phase segregation induced by the differences in the crystal structures of the two phases, accompanying a centrosymmetry breaking of the spherical CdS NPs. The CdS/CdTe heterodimers exhibited photoinduced spatial charge separation because of their staggered band-edge alignment.     

Bis(methylthio)tetracenes: synthesis, crystal-packing structures, and OFET properties

5,12-Bis(methylthio)tetracene (2) and 5,11-bis(methylthio)tetracene (3) were synthesized. DFT calculations indicate that the HOMO and LUMO energy levels of 2 and 3 are lowered by 0.13-0.24 eV and their HOMO-LUMO energy gaps are reduced by 0.1 eV relative to those of tetracene. X-ray crystallographic data revealed that 2 is arranged as a result of a 1-D slipped-cofacial π-stacking with S-S and S-π interactions, similar to the packing arrangement of 6,13-bis(methylthio)pentacene (1), whereas 3 exhibits a herringbone packing arrangement without S-S interactions. The OFET devices fabricated using spin-coated films of soluble 1 and 2, with a bottom-contact device configuration, exhibited hole mobilities as high as 1.3 × 10(-2) and 4.0 × 10(-2) cm(2) V(-1) s(-1) with current on/off ratios of over 10(5) and 10(4), respectively.     

Correlation between shapes of Shockley stacking faults and structures of basal plane dislocations in 4H-SiC epilayers

Abstract

Shockley-type stacking faults expanded in 4H–SiC epilayers induced by ultraviolet illumination were investigated using a photoluminescence imaging method, a photoluminescence mapping method and X-ray topography. After ultraviolet illumination, more than 30 patterns of Shockley-type stacking faults which expanded from perfect basal plane dislocations were observed by photoluminescence imaging. The initial basal plane dislocations were crystallographically classified, and individual shapes of expanded Shockley-type stacking faults were predicted. The correspondence between the predicted shapes and observed ones was discussed.     

The Effect of Trifluoromethyl and Difluoromethoxy Groups on Mesomorphic Properties

Abstract

This paper describes the effect of terminal substituent on the mesomorphic properties in 3-and 4-(4-alkoxyphenoxycarbonyl)phenyl 3- and 4-R-benzoate and 4-(4-alkoxybenzoyloxy)phenyl 2-, 3-, and 4-R-benzoates (R = CF₃, OCF₃, OCF₂H). The meta-trifluoromethoxy and para-difluoromethoxy compounds tend to show a smectic C phase, as well as smectic A and nematic ones, and introduction of a chiral carbon in the alkoxyl group induces the chiral smectic C one.     

Advantages of a monochromator for bandgap measurements using electron energy-loss spectroscopy

The practical advantages of a monochromator for electron energy-loss spectroscopy (EELS) in transmission electron microscopy are reviewed. The zero-loss peaks (ZLPs) of a monochromator and a cold field emission gun are compared in terms of bandgap measurement performance. The intensity of the ZLP tails at the bandgap energy is more important than the full-width at half maximum of the ZLP, and a monochromator is preferable to conventional electron sources. The silicon bandgap of 1.1eV is evaluated from the onset in the EEL spectrum obtained using the monochromator without a numerical procedure. We also show a high-speed instability-correction technique to realize the inherent energy resolution of the monochromator, in which instabilities of less than 335Hz are corrected using 512 EEL spectra obtained with an exposure time of 1.4ms. It will be useful in bandgap measurements and advanced studies for elucidating sub-eV EEL spectra.     

Surface EXAFS via differential electron yield

Surface‐sensitive analysis via extended X‐ray absorption fine‐structure (EXAFS) spectroscopy is demonstrated using a thickness‐defined SiO₂ (12.4 nm)/Si sample. The proposed method exploits the differential electron yield (DEY) method wherein Auger electrons escaping from a sample surface are detected by an electron analyzer. The DEY method removes local intensity changes in the EXAFS spectra caused by photoelectrons crossing the Auger peak during X‐ray energy sweeps, enabling EXAFS analysis through Fourier transformation of wide‐energy‐range spectral oscillations. The Si K‐edge DEY X‐ray absorption near‐edge structure (XANES) spectrum appears to comprise high amounts of SiO₂ and low Si content, suggesting an analysis depth, as expressed using the inelastic mean free path of electrons in general electron spectroscopy, of approximately 4.2 nm. The first nearest neighbor (Si—O) distance derived from the Fourier transform of the Si K‐edge DEY‐EXAFS oscillation is 1.63 Å. This value is within the reported values of bulk SiO₂, showing that DEY can be used to detect a surface layer of 12.4 nm thickness with an analysis depth of approximately 4.2 nm and enable `surface EXAFS' analysis using Fourier transformation.     

Instability analysis and simulation of water infiltration into an unsaturated elasto-viscoplastic material

A linear instability analysis was performed in order to investigate which variables have a significant effect on the onset of the instability of an unsaturated viscoplastic material subjected to water infiltration. It was found that the onset of the growing instability of the material system mainly depends on the specific moisture capacity, the suction, and the hardening parameter. Then, in order to simulate the water infiltration process of a one-dimensional unsaturated soil column, a multiphase coupled elasto-viscoplastic finite element analysis was performed based on the theory of porous media. The results of the numerical simulations are discussed with respect to the effect of the specific moisture capacity and the initial suction on the development of volumetric strain. We found that rapid transitions from unsaturated to saturated states and higher levels of initial suction lead to the contractive behavior of the material and instability. The instability detected by the numerical results is consistent with the theoretical results obtained through the linear instability analysis.     

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.