Microstructures and mechanical properties of Sb-doped ZnO thin films deposited on a-plane sapphire substrates

The structural features and nanomechanical properties of ZnO and Sb-doped (1.0 at%) ZnO (SbZO) thin films deposited on a-plane sapphire substrates by radio-frequency (RF) magnetron sputtering are comparatively investigated in this study. The X-ray diffraction and atomic force microscopy analyses indicated that both ZnO and SbZO thin films were highly (002)-oriented albeit with somewhat different grain structure and surface morphologies. Nanoindentation results of both films exhibited apparent discontinuities (so-called pop-ins) in the load-displacement curves (P-h curves), while no discontinuity was observed in the unloading segment of the P-h curves. By using a Berkovich nanoindenter operating with the continuous contact stiffness measurement mode, the obtained hardness and Young's modulus of ZnO (SbZO) thin films are 7.3 ± 0.2 (8.5 ± 0.4) GPa and 259.6 ± 17.8 (327.4 ± 13.9) GPa, respectively. Furthermore, the facture toughness and fracture energy of ZnO and SbZO thin films obtained by Vickers indentation were also compared.