*3.1. Surface Morphology of Micro-Structure of Al Template*

In this work, micro-powder blasting was carried out to form a micron-scale surface on an aluminum template, which was then anodized to produce nanoholes in anodic alumina. Finally, the micro/nano-structure of the aluminum template was formed. The first goal was to form a suitable micro-structured surface of aluminum using various sand particles on micro-powder blasting (Figure 2). The depth of the surface of the aluminum micro-structure declined as the diameter of the sand particles declined (Figure 2a–c). The results also reveal that surfaces which had been impacted by larger sand particles were more concave and convex. Figure 2d demonstrates that the depth of the surface micro-structure of aluminum that underwent impact by round sand particles was less than that which underwent impact by sharp sand particles. The results also indicate that the micro-structure surface of aluminum that underwent impact by round sand particles was smoother than that by sharp sand particles.

**Figure 2.** SEM images of Al template by powder blasting processing: (**a**) MS 245A (Φ = 50–250 μm); (**b**) MS 300A (Φ = 30–70 μm); (**c**) MS 550A (Φ = 10–20 μm); (**d**) MS 550BT (Φ = 20–30 μm).
