*2.1. Materials*

Specimens were prepared from circular aluminum (Al) templates (99.9%, thickness = 1 mm, Φ = 15 mm) using various processes. To prepare a flat-structure specimen, the Al template was electropolished in a solution of perchloric acid and ethanol (HClO4:C2H5OH = 1:4) at 7 ◦C for 2 min to remove surface irregularities.

#### *2.2. Micro-Structure of Al Template*

A micro-structured Al template was prepared. A micro-blasting machine (MICROPEEN 1300 ZP/ZPD, Iepco, Leuggern, Switzerland) was used to perform micro-powder blasting on Al template (99.9%). The micro-powder blasting formed irregular concave micron-sized holes on the surface of the aluminum template. This method increased the surface roughness of the aluminum. The sands used for micro-powder blasting were MS 245A, MS 300A, MS 550A and MS 550BT (A means sharp sand, BT means round sand), with a diameters of 50–250, 30–70, 10–20, and 20–30 microns, respectively. To form an aluminum template with micro-structure, a blasting pressure of six bars was utilized; the distance between the blasting nozzle and the template was 3 cm; two blasting times were used in each case, and four kinds of sand particles were used.
