*2.5. Measurement*

The contact angle of a water droplet on the surface was measured to analyze the corrosion resistance by the wettability. The water droplets were placed on the surface by a microsyringe and then the measurement of the contact angle was conducted for each sample at least five times. The mean value was used as the result value. Low contact angle (high wettability) means that a water droplet is spread over a relatively wide area of the surface. It can be easily attacked by corrosion due to its large interaction area. In contrast, a water droplet having a high contact angle interacts with a small region on the surface (low wettability). Field Emission Scanning Electron Microscope (FE-SEM, JSM-7100F) was utilized for SEM images.

#### **3. Results and Discussion**
