Si microwell arrays containing Pt–Pd thin film were fabricated by the chemical etching of a Si substrate through a polystyrene honeycomb mask using a patterned metal catalyst. The honeycomb mask, which was formed by the utilization of binary colloidal crystals composed of large silica spheres and small polystyrene spheres, acted as a mask for metal deposition. After immersing a locally Pt–Pd-coated Si substrate into a solution containing hydrofluoric acid and hydrogen peroxide, an ordered Si microwell array with a hexagonal arrangement could be obtained by site-selective metal-assisted chemical etching. Moreover, the notable feature of this process is that an isolated circular Pt–Pd film used as a catalyst remained at the bottom of each well after chemical etching.

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Nano/microstructure control and electrochemical etching of aluminium substrate using a honeycomb alumina mask fabricated by anodisation with self-assembled spheres aligned on the aluminium surface were studied to directly control the initiation sites of pits. The transfer of the hexagonally ordered pattern of self-assembled spheres to the aluminium substrate could be achieved by substantially suppressed anodic oxide growth under the spheres where selective electrochemical etching proceeded. That is, etch pits are generated only in the thinner areas or holes of the honeycomb alumina mask with a one-to-one correspondence. With this process, improvements in pit distribution density and the homogeneity of pit sizes, while avoiding excessive dissolution of the aluminium surface, could be achieved easily in comparison with the conventional method. The density of pits could also be controlled by changing the diameter of spheres used as an indirect mask.

Periodic inverted pyramid arrays in silicon were fabricated using a nonlithographic technique combining the localized anodization of the substrate and the subsequent anisotropic chemical etching in an alkali solution. A silicon oxide layer with a honeycomb pattern, which was produced by the anodization of a silicon substrate coated with self-assembled microspheres, served as a passivation layer for alkaline etching. After the removal of microspheres, the unoxidized silicon region was etched selectively by chemical etching in tetramethyl ammonium hydroxide, resulting in the formation of ordered inverted pyramid arrays in silicon. The interval between inverted pyramid holes could be controlled by changing the diameter of the spheres used as an initial mask for silicon anodization.