Scanning electron microscopy (SEM) of the film samples was performed using a Hitachi 570 SEM (FESEM Hitachi S4160, Japan) in the School of Metallurgy and Materials Engineering University of Tehran, Tehran Iran. The film samples (10 mm 10 mm 0.1 mm) were immersed in liquid nitrogen and cryo-fractured by hand. SEM pictures with 1500 magnification were taken with an accelerating voltage of 20 kV.