Electrochemical growth of multisegment nanoporous tin oxide layers by applying periodically changed anodizing potential

Multilayered nanoporous tin oxide films were synthesized via potential-controlled one-step anodic oxidation of metallic Sn in 1 M NaOH electrolyte at sequentially changed anodizing potential. The proposed method is based on the fact that nanoporous layers with much smaller (<15 nm) nanochannels are formed on the surface of metallic substrate at the potential of 2 V. On the contrary, when anodizing potential of 4 V is applied, oxide films with much larger pores (40–50 nm) are created. Moreover, it was also found that the thicknesses of individual segments can be precisely adjusted by controlling anodizing duration. As formed anodic films were mechanically stable with no internal cracks and discontinuities in the oxide structure.