Anodic porous alumina with square holes through lattice conversion of naturally occurring ordered structures

Anodic porous alumina with square cells and square holes was fabricated through the conversion of the triangular lattice of naturally occurring anodic porous alumina to a square lattice. A pattern of a triangular lattice obtained from an ordered anodic porous alumina lattice was converted to a pattern of a square lattice by modifying the ratio of the lattice through the anisotropic deformation of a polymer sheet with a triangular pattern transferred from porous alumina. The obtained pattern of a square lattice on the polymer sheet was transferred to a metal mold using a template process, and the pretexturing of Al using the obtained mold generated anodic porous alumina with square cells and square holes. The process allows the fabrication of anodic porous alumina with square cells and square holes without the use of a lithographic technique. The obtained porous alumina was applied to the fabrication of a surface-enhanced Raman scattering (SERS) substrate with a square Au nanodot array.