Figure 2

AFM images (500 nm × 500 nm) of a PAA fabricated in the mixture of 20 wt% H₂SO₄, 1 wt% citric acid and 1 wt% Al₂(SO₄)₃ under 15°C and 10 V for 30 min, b PAA fabricated in 0.3 M oxalic acid under 15°C and 2 V for 30 min, c three-dimensional AFM image (1 μm × 1 μm) of PAA fabricated in 0.3 M oxalic acid under 15°C and 10 V for 30 min, d AFM image (1 μm × 1 μm) of PAA fabricated in a mixture of 0.3 M oxalic acid, 0.1 M Al₂SO₄ and 1 wt% ethylene glycol at 60°C for 30 min