3.1.1. Structural Analysis

The surface morphologies of the samples were analyzed by using the AFM method with a scanning area of 40 <sup>×</sup> 40 <sup>μ</sup>m2, as well as SEM. AFM and SEM images for the surface morphologies of AZO films on glass and PET (before and after bending) are shown in Figure 1a–f. The surface of the films on glass was reasonably smooth, with a roughness of < 3 nm. Grain growth was dense with highly homogenous distribution, as clearly seen in the 3-D AFM image of the surface. It is well known that the grain size, the distribution and the surface roughness are influenced by the sample thickness [16]. The measured root mean square (RMS) roughness of AZO/glass was about 2.3 nm. As seen from the SEM, the as-grown AZO films on both substrates–glass and PET are relatively smooth, with a uniform distribution of slightly elongated grains. The average grain size of AZO films is approximately the same, around 20 nm. The RMS roughness of AZO/PET and SEM morphology before and after bending are discussed in Section 3.1.4.

**Figure 1.** Atomic Force Microscopy (AFM) and SEM analysis of aluminum-doped zinc oxide (AZO) layers deposited on (**a**,**b**) AZO/glass (**c**,**d**) AZO/polyethylene terephthalate (PET) (before bending test) and (**e**,**f**) AZO/PET (after bending 1000 times, discussed in 3.1.4.).
