3.1.2. FESEM
The FESEM images of the nanofibers before and after annealing are shown in Fig. 2(a–i), respectively. The surface of the nanofibers is smooth and beadless with random orientation. According to the fiber diameter distribution histogram shown in Fig. 2(j–r), the average diameter of the nanofibers can be obtained and the results are listed in Table 1. The average diameters of the annealed nanofibers (Fig. 2(m–r)) slightly reduced in comparison to the “as spun” nanofibers (Fig. 2(j–l)). As discussed in the TGA–DTA sec- tion, up to 430◦C, PVA, acetate and nitrate group in the “as spun” nanofibers decompose and the crystallization of ZnO occurred at about 235 ◦ C. Therefore, reduction in the average diameter after annealing is due to the decomposition of the organic substances and ZnO crystallization [7]. From Table 1, it is obvious that the aver- age diameter of the samples increased slightly with increasing the amount of CdO. In addition, by increasing the annealing rate from 3 to 20 ◦ C/min, the morphology of nanofibers exhibited a mild shrink- age and the average diameter decreased. This could be due to the decrement in the remaining amount of the annealed electrospun nanofibers that is verified in TGA data (see Fig. 1).