Lithographically Formed Fine Wavy Surface Morphology for Universal Alignment Control of Mesochannels in Mesostructured Silica Films

Full-Multiscale Spontaneous Organization for Optically Anisotropic Titania Films

Titania films with a completely controlled hierarchical structure, at microscopic, mesoscopic, and macroscopic scales, are successfully prepared by carefully combining "top-down" and "bottom-up" nanoprocesses. The titania films are composed of regularly arranged anatase nanocrystals, which form a 2D hexagonal mesostructure with cylindrical mesopores. Furthermore, the cylindrical mesopores are aligned in one direction in the plane of the film over the whole area. Thus, hierarchical structural regularities over multiple length scales, i.e., atomic (10-10 m), mesoscopic (10-8 m), and macroscopic (10-2 m) scales, are achieved. The mesoporous titania films with a controlled alignment are prepared via sol-gel chemistry using the self-assembly process of amphiphilic molecules combined with a lithographically prepared anisotropic substrate with a fine wavy cross-section. The carefully designed sol-gel process using Pluronic P123 as a structure-directing agent allows the retention of the aligned mesoporous structure as well as the formation of crack-free films even after the crystallization of titania. The anisotropic mesoporous structure with pore walls composed of high-refractive-index crystalline titania exhibits remarkable optical anisotropy, birefringence. This full-multiscale structural control of an inorganic material, from atomic to centimeter scales, affords distinguished functionalities to artificially prepared nanomaterials, paving the way for creating new values.

Mesoporous ordered films via self-assembly: trends and perspectives

The synthesis of ordered mesoporous films via self-assembly represents one of the main accomplishments in nanoscience. In fact, controlling the complex chemical-physical phenomena that govern the process triggered by the solvent's fast evaporation during film deposition has represented a challenging task. Several years after the first articles on the subject, the research in the field entered a new stage. New advanced applications based on the peculiar properties of mesoporous films are envisaged while basic research is still going on, especially to clarify the mechanism behind self-organization in a spatially defined environment and the physics and chemistry in mesoscale porosity. This review has been dedicated to analysing the main trends in the fields and the perspective for future developments.

Increasing the Diameter of Vertically Aligned, Hexagonally Ordered Pores in Mesoporous Silica Thin Films

The variation in pore size in mesoporous films produced by electrochemically assisted self-assembly (EASA) with the surfactant chain length is described. EASA produces a hexagonal array of pores perpendicular to the substrate surface by using an applied potential to organize cationic surfactants and the resultant current to drive condensation in a silica sol. Here, we show that a range of pore sizes between 2 and 5 nm in diameter is available with surfactants of the form [Me₃NC_nH_2n+1]Br, with alkyl chain lengths between C₁₄ and C₂₄. The film quality, pore order, pore size, and pore accessibility are probed with a range of techniques.