No abstract

Bottom-up fabrication of nanopatterns with single nanometer-scale periodicity is quite challenging. In this study, we have focused on the use of the outermost convex surfaces of lyotropic liquid crystals (LLCs) as a template. Periodically arrayed single nanometer-scale nanogrooves consisting of silica are successfully formed on a Si substrate covered with LLCs composed of cylindrical micelles of cetyltrimethylammonium chloride. Soluble silicate species are generated from the Si substrate by a treatment with an NH-water vapor mixture, infilling the interspaces between the Si substrate and the LLCs. The cross section of the nanogrooves has a symmetrical sawtooth-like profile with a periodicity of 4.7 nm, and the depth of each nanogroove is around 2 nm. Uniaxial alignment of the nanogrooves can be achieved using micrometer-scale grooves fabricated by a focused ion beam technique. Although formed nanogrooves contain defects, such as bends and discontinuities, this successful concept provides a novel fabrication method of arrayed concave patterns with sub-5 nm periodicity on the surfaces of Si substrates.

A series of nickel(II) complexes of a 2,6-dihydroxynaphtho-1-aldehyde Schiff base was synthesized. By means of in situ formation of metal-containing tectons, some of those complexes afforded sub-millimeter-scale single crystals directly from the reaction mixture. The complexes consisted in part of various ladder-like hydrogen-bonded networks, which forced the chromophore to arrange in anisotropic fashion, with the effect dependent on the length of the alkyl chains. The crystals exhibited a marked linear dichroism, and their solid-state polarization absorption spectra were recorded with an optical microscope. Using data from quantum chemical calculations and the crystal structure, we were able to elucidate the relationship between crystal packing and optical anisotropy. Analyses based on theoretical equations allowed us to explain the observed absorbance and to interpret the mechanism of the dichroism in detail.

Self-healing materials that can spontaneously repair damage under mild conditions are desirable in many applications. Significant progress has recently been made in the design of polymer materials capable of healing cracks at the molecular scale using reversible bonds; however, such a self-healing mechanism has rarely been applied to rigid inorganic materials. Here, we demonstrate the self-healing ability of lamellar silica-based thin films formed by self-assembly of silica precursors and quaternary ammonium-type surfactants. Specifically, spontaneous healing of cracks (typically less than 1.5 μm in width) was achieved under humid conditions even at room temperature. The randomly oriented lamellar structure with thin silica layers is suggested to play an essential role in crack closure and the reformation of siloxane networks on the fracture surface. These findings will lead to the creation of smart self-healing silica-based materials based on reversible siloxane bonds.