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Figure 6 | Nanoscale Research Letters

Figure 6

From: AFM, SEM and TEM Studies on Porous Anodic Alumina

Figure 6

FESEM images of PAAs’ evolvements, a two-layer PAA sample with upper larger pores and bottom smaller pores, which is first anodized under 160 V at 0°C for 20 min in 5 wt% H3PO4 and second anodized 40 V at 30°C for 2 h in 0.3 M oxalic acid, b two-layer PAA structure fabricated under 180 V at 20°C in the mixture of 5 wt% phosphoric acid, 1 wt% citric acid and 5 wt% ethanol, c three-layer configuration by three-step anodization at 150 V for 1 min, 40 V for 25 min and 150 V for 1 h, d a typical cross-section of PAA fabricated under 40 V at 0°C in 0.3 M oxalic acid for 10 h, e combined nanopore-microstep hierarchical structure, which is obtained by first anodization under 5 V and 0°C in a mixture of 1 wt% H3PO4, 0.42 wt% NaCl and 20 wt% ethanol, and second anodization under 40 V and 40°C in 0.3 M oxalic acid, f upper aluminum micro-scale step structure with lower general PAA layer, which is obtained by first anodization in oxalic acid and second anodization on the other side in Cl containing electrolyte until the current dropped dramatically. The anodizing condition in (f) is as same as that in (e)

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