A composite material that leads to self organization of mesogen-coated gold nanospheres is synthesized and shows enhanced anisotropic optical properties due to synergistic effects of the mesogens intrinsic birefringence and its ability to drive the self-assembly process into highly anisotropic architectures with densely packed nanospheres. Such nanoengineered matter sustains a response beyond that achievable by its individual constituents, i.e., a metamaterial.
Small-angle X-ray scattering (SAXS) and atomic force microscopy (AFM) were used to study orientation patterns of two polyphilic liquid crystals (LC) confined to cylindrical pores of anodic aluminum oxide (AAO). The hierarchical hybrid systems had the LC honeycomb (lattice parameter 3.5-4 nm) inside the pores of the AAO honeycomb (diameters 60 and 400 nm). By conducting complete reciprocal space mapping using SAXS, we conclude that the columns of both compounds align in planes normal to the AAO pore axis, with a specific crystallographic direction of the LC lattice aligning strictly parallel to the pore axis. AFM of LC-containing AAO fracture surfaces further revealed that the columns of the planar anchoring LC (compound 1) formed concentric circles in the plane normal to the pore axis near the AAO wall. Toward the pore center, the circles become anisometric "racetrack" loops consisting of two straight segments and two semicircles. This mode compensates for slight ellipticity of the pore cross section. Indications are, however, that for perfectly circular pores, circular shape is maintained right to the center of the pore, the radius coming down to the size of a molecule. For the homeotropically anchoring compound 2, the columns are to the most part straight and parallel to each other, arranged in layers normal to the AAO pore axis, like logs in an ordered pile. Only near the pore wall the columns splay somewhat. In both cases, columns are confined to layers strictly perpendicular to the AAO pore axis, and there is no sign of escape to the third dimension or of axial orientation, the latter having been reported previously for some discotic LCs. The main cause of the two new LC configurations, the "racetrack" and the "logpile", and of their difference from those of confined nematic LC, is the very high splay energy and low bend energy of columnar phases.
Here, two dimensional Nb2C quantum dots with green fluorescence were fabricated for the first time with a quantum yield (QY) of up to 19%, the highest reported for Nb2C dots so far with good photostability and pH stability.
Two-dimensional (2D) photo- and electrocatalysts play a key role in hydrogen production through water splitting, and much efforts have been undertaken to seek a low-cost and efficient alternative candidate to noble-metal Pt. Herein, the method of introducing several different transition-metal atoms to tune the catalytic properties of 2D MBene is proposed. Density functional theory calculations reveal that the H–O bonding strength can be weakened by charge transfer between the oxygen atom and the introduced single-metal atom. The weakening of the bond greatly improves the MBene catalytic activity of hydrogen evolution reaction. Interestingly, the Gibbs free energy (|ΔG H|) of W2B2O2 decreases from |−0.67| to 0.013 eV by embedding a V adatom. This work should initiate 2D material MBene applications in green catalysis and energy sectors.
(max. 250 words):Metamaterials today are often realized as complex structured metasurfaces. Their functionality is based on combination of plasmonic resonances in metallic nanostructures and interferences. Novel concepts of bottom up fabrication using liquid crystal self-organization promise the realization of bulk metamaterials. Only very view such composite self organizing materials based on liquid crystals are demonstrated up to now. In detail we use rod like nematic liquid crystal molecules that are grafted onto gold nanoparticles. Structural analysis is done by X-ray scattering experiments that revealed an arrangement of the nanoparticles in chains similar to the ones found in columnar phases. To aspect are of particular importance: The sufficient size of nanoparticles to achieve efficient plasmon resonance effects and the ligands anchored on the particles that control the self-assembling properties. The combined effect of the ligands birefringence and the anisotropic arrangement of the plasmonic nanoparticles lead to a strong polarization dependence of the metamaterial's optical properties. These results demonstrate the ability to fabricate a self ordered and tunable metamaterial by chemical engineering of the nanoparticles with liquid crystalline mesogenic ligands. In our contribution, we show experimental evidence of coupling resonances of metallic nanoparticles in an entire self-organizing material. We give details on the pathway to design such structures and to adjust their optical and mechanical properties. Theoretically insight of the electromagnetic properties is provided and the approaches to effective material design will be given. words summary:The electromagnetic response of Metamaterial can be managed by combining resonances and interferences of different materials and on different lengths scales. In our contribution we study composite metamaterials containing resonant plasmonic metallic nanoparticles that show organization. The material bases its nonconventional properties on short distance self-organization by mesogens that form a liquid crystal host material. We compare the properties of such materials with other model systems containing organized nanoparticles. Theoretically insight of the electromagnetic properties is provided and we give details on the pathway to design such structures and to adjust their optical and mechanical properties.
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