Quantifying the defect-dominated size effect of fracture strain in single crystalline ZnO nanowires

The diameter (D) dependence of fracture strains in [0001]-oriented single crystalline ZnO nanowires (NWs) with D ranging from 18 to 114 nm is experimentally revealed via in situ uniaxial tension and is well understood based on an analytical model developed by combining molecular dynamics simulations with fracture mechanics theories. We show that the scattered fracture strains are dominated by the effective quantities of atomic vacancies, and their lower bound follows a power-form scaling law, resembling the Griffith-type behavior of single critical defects with diameter-dependent sizes, when D is larger than a critical DC. In addition, theoretical strength is expected in NWs with D < DC. Our studies provide a simple, but basic, understanding for the size effect of strengths in single crystalline NWs.