Fabrication of polygonal nanoholes by localized mask-free wet anisotropic etching

Nanoholes integrated into microfluidic systems have been widely researched, due to their practical applications in biosensing fields. This paper is devoted to report a strategy for fabricating polygonal nanoholes by localized mask-free anisotropic etching. Underetching occurs at the pore mouth, causing shape modification of the original square nanohole prepared by wet etching. The influence of the etching under different etching temperatures, KOH concentrations, as well as KOH with isopropanol (IPA) addition, on the shape formation of nanoholes are carefully analyzed and verified by experiments. Under low etching temperature or low KOH concentration, the shape of nanohole turns to be dodecagonal. Under high etching temperature and high KOH concentration, the increase of etching rate of (331) planes promotes transition of the nanohole to an octagonal shaped. By adding IPA into KOH solution, the pore shape is limited to be dodecagonal, and it is irrelative to the etching temperature and KOH concentration.