*3.5. The Results of Null Hypothesis*

The null hypothesis was that surface modification methods (micro-powder blasting, anodized process, micro-powder blasting + anodized process) only has an effect on the surface of the Al template. The authors wanted to determine the depth of the Al template micro-structure or micro/nano-structure after surface modification. Figure 5 shows the surface profile of different structures of aluminum templates measured by AFM. The depth of the Al template was about 80.89 nm. The results show that the depths of the micro-structure of the Al template were 109.15 nm, 158.93 nm, and 164.52 nm for sand particles MS 245A, MS 300A, and MS 550BT by micro-powder blasting, respectively. The depth of AAO was 150.00 nm for the anodized process. The depth of Al template micro/nano-structure was 171.15 nm by the micro-powder blasting + anodized process. The previous results can reveal that the surface modification methods influence the surface layer of the Al template. The experimental results fit the null hypothesis.

**Figure 5.** Surface profile of different structures on aluminum templates: (**a**) Al template; (**b**) MS 245A; (**c**) MS 300A; (**d**) MS 550BT; (**e**) AAO; (**f**) micro/nano-structure without electrolysis polishing.
