Understanding focused ion beam guided anodic alumina nanopore development

► We study the effect of FIB patterning on pore evolution during anodization. ► FIB patterned concaves with 1.5 nm depth can effectively guide nanopore growth. ► The edge effect of FIB guided patterns causes nanopores to bend. ► Anodization window is enlarged to 50-80 V for 150 nm interpore distance hexagonal arrays.