Comparative investigation of fracture behaviour of aluminium-doped ZnO films on a flexible substrate

The differences in the fracture behaviour of aluminium-doped ZnO (AZO) films on a flexible substrate subjected to tensile and compressive strains were investigated by using a simple-support bending method. It is found that the crack density and the crack spacing of the AZO films become saturated both in the face-out (FO) and in the face-in (FI) bending tests when the applied strain reaches a certain value. The saturated crack density of the AZO film in the FO bending is higher than that of the film in the FI bending. Crack-initiation strain of the film in the FO bending is smaller than that of the film in the FI bending. The fracture energy of the AZO films is also analyszed. Failure behaviours of the films are examined and exhibit different failure mechanisms for the films subjected to tensile and compressive strains.