Effects of surface oxide layer on fracture toughness of submicrometer-thick freestanding copper films

Abstract

Fracture toughness experiments were conducted on ~ 500-nm-thick copper films with a thickness-controlled surface oxide layer and without an oxide layer. The fracture toughness of the films with a surface oxide layer was largely independent of the oxide layer thickness in the range of ~ 0.8–~5.9 nm. However, the fracture toughness of the films without the surface oxide layer was greater than that of the films with the surface oxide layer. A quantitative strain distribution measurement revealed that the absence of the surface oxide layer helped delocalize the plastic deformation ahead of the notch, thus increasing the fracture toughness.