Figure 4.

SEM images of AAO pores and changes in the Fabry-Perot fringe spectrum of AAO. SEM images of AAO pores with different d_w prepared by the pore-widening process in 10 wt.% phosphoric acid from 0 to 55 min: (a) 0, (b) 20, (c) 40, and (d) 50 min. The reduction of pore walls is marked by a red line. (e) Changes in the Fabry-Perot fringe spectrum of AAO observed during the pore-widening process (initial d_p = 30 nm).