Nano-scaled diffusional or dislocation creep analysis of single-crystal ZnO

The nanoindentation time-dependent creep experiments with different peak loads are conducted on c-plane (0001), a-plane (1120) and m-plane (1010) of single-crystal ZnO. Under nano-scaled indentation, the creep behavior is crystalline orientation-dependent. For the creep on (0001), the stress exponent at low loads is ∼1 and at high loads ∼4. The stress exponents under all loads are within 3∼7 for the creep on (1120) and (1010). This means that diffusion mechanism and dislocation mechanism is operative for different planes and loads. The relative difficulty of dislocations activation is an additional factor leading to the occurring of diffusion creep on the c-plane of single-crystal ZnO.