Formation of Nanogrooves with Sub-5 nm Periodicity Using Local Silicification at the Interspace between a Si Substrate and Lyotropic Liquid Crystals

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 NH₃-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.