Mesoporous anodic tin oxide with two-dimensional macroporous network

Here, we report a single-step anodic oxidation process to form a micron-scale island array of mesoporous tin oxide without any template. The grain boundary of an electrodeposited tin metal layer proved to be diffuse with a width of a few hundred nanometers. Such a diffuse boundary with high-surface energy might be preferentially dissolved during anodic oxidation to form a two-dimensional macroporous network in the mesoporous tin oxide film. In a mixed anodization solution of oxalic acid and an etchant of tin metal (i.e., methanol), the removal of the diffuse grain boundary was significantly promoted and led to a clear island array of mesoporous tin oxide. The size and density of the mesoporous tin oxide islands were tunable by varying the current density applied during the tin electroplating.