Figure 8

TEM images, a a single hexagonal cell of typical PAA fabricated in 0.3 M oxalic acid under 40 V at 0°C for just 1.5 min, b contrast variation in an image due to the thickness discrepancy in the sample that is fabricated in 0.3 M oxalic acid under 40 V at 0°C for 5 min c PAA with pore diameter of only 15 nm fabricated in 0.3 M oxalic acid under 12 V and 0°C for 3 min