Molecular statics simulations of the size-dependent mechanical properties of copper nanofilms under shear loading

• The size-dependence of the shear yield strength of copper nanofilms is examined.
• The origin of the size-dependence of the shear yield strength is analyzed.
• A Hall–Petch-like fitting function is proposed to predict shear yield strength.
• The generation of vacancy clusters is found to depend on film thickness.
• Three new patterns of vacancy cluster are observed.

Molecular statics simulations are conducted on single-crystal copper nanofilms subjected to shear loading to examine the effect of thickness on the mechanical properties of nanofilms. Simulation results show that not only the yield strength but also the shear modulus increases with decreasing film thickness. In order to better relate the yield strength of a copper nanofilm to its thickness, a Hall–Petch-like fitting function is proposed to predict the variation of yield strength with film thickness. The initial yield is found to be associated with the nucleation of dislocations. The energy required for the first nucleation of dislocations is calculated and plotted as a function of film thickness to elucidate the origin of the thickness effect on yield strength. In addition, the production of vacancy clusters is also found to depend on film thickness and three new patterns of vacancy clusters are observed in our simulations.