Synthesis, structure and luminescence properties of metal-organic frameworks based on benzo-bis(imidazole)

Metal-organic frameworks(MOFs)constructed from conjugated organic ligands are candidates for hybrid photoactive materials with potential applications.Compared to that from the ligands only,the intensity and wavelength of the luminescence could be tuned after they were incorporated in extended framework.In this report,by using an organic ligand with azolate moiety,benzo-bis(imidazole)(H2BBI),we synthesized two new MOF structures.Framework 1([Co(H2BBI)(DMSO)2Cl2]n,DMSO=dimethyl sulfoxide),constructed from tetrahedral Co(II)and H2BBI,exhibits zigzag 1D structure.Meanwhile,framework 2([Cu2(H2BBI)3(DMSO)6(NO3)4]n),a layered structure with hcb topology,was assembled from tetragonal pyramidal Cu(II)and H2BBI.Furthermore,2 exhibits strong luminescence emission(ex=280 nm).A blue shift of 40 nm(from 359 nm to 319 nm)was observed in framework 2 compared to the free ligand,which could be explained by the ligand-to-metal charge transfer in the network.     

A three‐dimensional CdII coordination framework: poly[di‐μ2‐aqua‐{μ2‐1,4‐bis[(1H‐1,2,4‐triazol‐1‐yl)methyl]benzene‐κ2N4:N4′}di‐μ3‐terephthalato‐κ3O:O′:O′′‐dicadmium(II)]

The title Cd^II coordination polymer, [Cd(C₁₀H₈O₄)(C₁₂H₁₂N₆)_0.5(H₂O)]_n, has been obtained by the hydrothermal method and studied by single‐crystal X‐ray diffraction, elemental analysis, thermogravimetric analysis, IR spectroscopy and fluorescence spectroscopy. The compound forms a novel three‐dimensional framework with 3,8‐connected three‐dimensional binodal {4.5²}₂{4².5¹⁰.6¹².7.8³} topology. An investigation of its photoluminescence properties shows that the compound exhibits a strong fluorescence emission in the solid state at room temperature.     

Topologically protected interface mode in plasmonic waveguide arrays

Recent realization of nontrivial topological phases in photonic systems has provided unprecedented opportunities in steering light flow in novel manners. Based on the Su–Schriffer–Heeger (SSH) model, a topologically protected optical mode was successfully demonstrated in a plasmonic waveguide array with a kinked interface that exhibits a robust nonspreading feature. However, under the same excitation conditions, another antikinked structure seemingly cannot support such a topological interface mode, which appears to be inconsistent with the SSH model. Theoretical calculations are carried out based on the coupled‐mode theory, in which the mode properties, excitation conditions, and the robustness are studied in detail. It is revealed that under the exact eigenstate excitations, both kinked and antikinked structures do support such robust topological interface modes; however, for a realistic single‐waveguide input only the kinked structure does so. It is concluded that the symmetry of interface eigenmodes plays a crucial role, and the odd eigenmode in a kinked structure offers the capacity to excite the nonspreading interface mode in the realistic excitation of a one‐waveguide input. Our finding deepens the understanding of mode excitation and propagation in coupled waveguide systems, and could open a new avenue in optical simulations and photonic designs.

     

Photonic Floquet topological insulators in atomic ensembles

The feasibility of realizing a photonic Floquet topological insulator (PFTI) in an atomic ensemble is demonstrated. The interference of three coupling fields will split energy levels periodically, to form a periodic refractive index structure with honeycomb profile that can be adjusted by different frequency detunings and intensities of the coupling fields. This in turn will affect the appearance of Dirac cones in momentum space. When the honeycomb lattice sites are helically ordered along the propagation direction, gaps open at Dirac points, and one obtains a PFTI in an atomic vapor. An obliquely incident beam will be able to move along the zigzag edge of the lattice without scattering energy into the PFTI, due to the confinement of edge states. The appearance of Dirac cones and the formation of a photonic Floquet topological insulator can be shut down by the third‐order nonlinear susceptibility and opened up by the fifth‐order one.

     

Microstructures and soft magnetic properties of Fe80P20-xSix (x = 4.5–6.5) amorphous ribbons

Fe-based amorphous ribbons with excellent soft magnetic properties and mechanical properties were prepared in the Fe–Si–P ternary system. Enhanced soft magnetic properties could be achieved through annealing treatment of the ribbons for 1 h at 325 °C, which is far below the glass transition temperatures (462–474 °C). Icosahedral medium-range ordering with a size range of around 2 nm occurred throughout the amorphous matrix during the low-temperature annealing treatment. The annealed ribbons exhibited improved magnetic saturation of over 185 emu/g while maintaining good mechanical flexibility. During icosahedral ordering, the distance between the Fe atoms and the coordination number within the amorphous ribbon can be optimised for achieving high magnetic saturation. However, nanocrystallisation of the SiP and Fe₂P transition phases embedded within the amorphous matrix occurred after the annealing treatment for 1 h at 385 °C, which caused deterioration of the soft magnetic properties and mechanical flexibility of the ribbons. Therefore, the combination of high magnetic saturation and mechanical flexibility of the amorphous ribbons could be optimised through low-temperature annealing treatment without any nanocrystallisation.     

Bulk and surface electron transport in topological insulator candidate YbB6–δ

We report the study of transport and magnetic properties of the YbB_6–δsingle crystals grown by inductive zone melting. A strong disparity in the low temperature resistivity, Seebeck and Hall coefficients is established for the samples with the different level of boron deficiency. The effective parameters of the charge transport in YbB_6–δ are shown to depend on the concentration of intrinsic defects, which is estimated to range from 0.09% to 0.6%. The pronounced variation of Hall mobility μ_H found for bulk holes is induced by the decrease of transport relaxation time from τ ≈ 7.7 fs for YbB_5.994 to τ ≈ 2.2 fs for YbB_5.96. An extra contribution to conductivity from electrons with μ_H≈ –1000 cm² V^–1 s^–1 and the very low concentration n /n_Yb≈ 10^–6 discovered below 20 K for all the single crystals under investigation is suggested to arise from the surface electron states appeared in the inversion layer due to the band bending. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Topological nature of in‐gap bound states in disordered large‐gap monolayer transition metal dichalcogenides

We propose a physical model based on disordered (a hole punched inside a material) monolayer transition metal dichalcogenides (TMDs) to demonstrate a large‐gap quantum valley Hall insulator. We find an emergence of bound states lying inside the bulk gap of the TMDs. They are strongly affected by spin–valley coupling, rest‐ and kinetic‐mass terms and the hole size. In addition, in the whole range of the hole size, at least two in‐gap bound states with opposite angular momentum, circulating around the edge of the hole, exist.Their topological insulator (TI) feature is analyzed by the Chern number, characterized by spacial distribution of their probabilities and confirmed by energy dispersion curves (energy vs. angular momentum). It not only sheds light on overcoming low‐temperature operating limitation of existing narrow‐gap TIs, but also opens an opportunity to realize valley‐ and spin‐qubits. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Topological transition in coated wire medium

Employing nonlocal homogenization approach, we investigate the properties of a metamaterial consisting of parallel metallic wires with dielectric coating. We demonstrate that manipulation of dielectric contrast between wire dielectric shell and host material at fixed frequency results in dynamic switching of metamaterial dispersion regime from elliptic to the hyperbolic one, i.e. the topological transition takes place. It is proved that such transition can be induced by the variation of the metamaterial temperature. Our findings thus pave a way to the implementation of a tunable ‘elliptic‐hyperbolic’ metamaterial.     

Geometric phase in a composite system subjected to decoherence

In this paper, we investigate the geometric phase of a composite system which is composed of two spin- particles driven by a time-varying magnetic field. Firstly, we consider the special case that only one subsystem driven by time-varying magnetic field. Using the quantum jump approach, we calculate the geometric phase associated with the adiabatic evolution of the system subjected to decoherence. The results show that the lowest order corrections to the phase in the no-jump trajectory is only quadratic in decoherence coefficient. Then, both subsystem driven by time-varying magnetic field is considered, we show that the geometric phase is related to the exchange-interaction coefficient and polar angle of the magnetic field.     

Scaling Up DNA Origami Lattice Assembly

The surface-assisted hierarchical assembly of DNA origami nanostructures is a promising route to fabricate regular nanoscale lattices. In this work, the scalability of this approach is explored and the formation of a homogeneous polycrystalline DNA origami lattice at the mica-electrolyte interface over a total surface area of 18.75 cm² is demonstrated. The topological analysis of more than 50 individual AFM images recorded at random locations over the sample surface showed only minuscule and random variations in the quality and order of the assembled lattice. The analysis of more than 450 fluorescence microscopy images of a quantum dot-decorated DNA origami lattice further revealed a very homogeneous surface coverage over cm² areas with only minor boundary effects at the substrate edges. At total DNA costs of € 0.12 per cm², this large-scale nanopatterning technique holds great promise for the fabrication of functional surfaces.