Consideration on functional surface design by depositing various materials with specific pattern

This paper discusses surface functional design by depositing various materials with regular pattern. First, three examples are introduced: (1) Thermal conductivity of pitch-type carbon fiber is higher than those of metals and thus the chopped fibers were deposited with spray coating on a resin plate to increase the overall thermal conductivity along the plate. (2) Silver nanoparticles were deposited and fixed keeping regular spacing, and attainable antibacterial activity was examined to make clear the minimum quantity of expensive silver particles. (3) Silica particles were self-assembled on a silicon wafer configuring lattice pattern to compromise both of optical reflectivity and wettability. It was confirmed that deposited particles shorten the drying time because the pinning hold the droplet edge and thus the surface area large, while reflectivity was kept by the smooth surface between the lattice particles pattern. Spatial frequency of the surface structure was often discussed as well as the material property, because regular cross-sectional profile or texture often changes the surface functionality. Finally, design methodology was discussed. Assuming different functions are related to respective spatial frequency component of the texture or material deposition, and the combination of plural frequency components should be integrated on the surface cross sectional profile to compromise plural functions simultaneously. Case study was the combination of friction, wettability and optical functions

Fabrication of High Aspect Ratio Silicon Nanostructure with Sphere Lithography and Metal-Assisted Chemical Etching and its Wettability

Metal-assisted chemical etching (MACE) is a site-selective etching process produced by a catalyst reaction at the interface between noble metal and silicon. This paper aims to make clear the applicability of sphere lithography and MACE to the fabrication of high aspect ratio Si nanostructures. The capacity to control the etched profiles and the scale extension are investigated. First, silica particles (e.g. φ1 μm) were self-assembled on a Si substrate. After the reduction of particle size via argon ion bombardment, a gold layer was deposited using the particles as a mask. The substrate was then etched with a mixture of hydrofluoric acid and hydrogen peroxide. It was found that an array of nanopillars with a regular pitch, good separation, and an aspect ratio of about 52 was produced. The effects of MACE conditions on final profiles were clarified. A limitation of this approach is the small (several millimeters) area fabricated due to the dependence on the vacuum technique (ion bombardment, Au deposition), and the size of the area limits its practical applications. Thus, Ag nanoparticles (e.g. φ150 nm) were applied. The relationship between the concentration of the Ag suspension, the Ag assembled layer, and the morphology of MACE structures was made clear. A spray method was applied to extend the deposited area of Ag particles up to φ100 mm. Finally, the effects of the cross-sectional profile on the contact angle of a water droplet were examined. By applying a high aspect ratio nanostructure on the substrate, the water contact angle increased up to 153 degrees while that without the structure is 58 degrees

Fabrication of high aspect ratio silicon micro-/nano-pore arrays and surface modification aiming at long lifetime liquid-infused-type self-cleaning function

This paper discusses a fabrication process of high aspect ratio (AR) silicon micro-/nano-pore structures and modification of their surfaces to improve the function of liquid-infused-type self-cleaning surfaces. The structure and its hydrophobic surface play an important role to hold a special liquid (a lubricant) on the surface tight to produce an intermediate lubricant layer and any liquid drops, including low surface tension liquids such as oil, can slide easily on it. The nanopore structure with an AR as high as 30 was fabricated by etching in a solution of hydrofluoric acid and hydrogen peroxide. This process based on a catalyst reaction of an array of Au islands that was deposited on a silicon substrate through a particle mask. This original hydrophilic surface was changed to hydrophobic one by depositing self-assembled monolayer of octadecyltrichlorosilane to modify the energy balance at the interface of the solid structure, the lubricant, another liquid, and air. Then the lubricant could be well retained. The functional lifetime was evaluated by measuring the liquid residue on the surface after number of liquid dash. It was confirmed that longer lifetime was obtained with higher AR nanopore structure