Size-dependent piezoelectricity in zinc oxide nanofilms from first-principles calculations

The size dependence of the piezoelectricity in ZnO nanofilms is investigated using ab initio density-functional theory calculations. The effective piezoelectric constant of ZnO nanofilms increases monotonically with increasing film thickness in the nanoscale simulated in the present work, and surprisingly, exceeds that of the bulk ZnO when the thickness is greater than 2.4 nm. The enhancement over the bulk value reaches 11% when the film thickness is 2.9 nm.