Figure 4.

Schematic procedure of hemisphere curved surface formation through the impurity during two-step anodization. (a) Joule heat caused by impurity, (b) difference of grow rate, (c) removal of all porous alumina, and (d) the second anodization.

Chung et al. Nanoscale Research Letters 2011 6:596   doi:10.1186/1556-276X-6-596
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