**2.4 Lift-off and etching process**

In this study, lift-off and etching processes were used to fabricate the different textures of the 304BA SS substrates. The striped texture was created on the 304BA SS substrate using the lift-off process. After the hard-baking process, a silver (Ag) thin film was deposited on the substrate by e-beam evaporation. An acetone solution was used to remove the residual photo resistor (PR). The depth of the striped texture was controlled by the thickness of the Ag thin film deposited. Four different striped textures were created on the 304BA SS substrates, including period/height: 6/0.1, 6/0.3, 12/0.1 and 12/0.3 μm. Two other types of textured 304BA SS substrate, the ridged-stripe and pyramid texture with 22.5 μm width were created by the etching process. After hard-baking, the 304BA SS substrate was etched by aqua regia (HNO3 : HCl : DI water=1 : 3 : 4). The etching temperature was 28-35℃ with an etching time of 7-12 min. to control the etching depth of the textured 304BA SS substrate. The detail experimental flow charts of lift-off and etching processes are shown in Fig. 4 and Fig. 5, respectively.
