Plane stress fracture toughness of freestanding nanoscale thin films

Fracture toughness values of notched thin films were measured in-situ in the scanning electron microscope using a micro-machined experimental setup. Freestanding specimens, 200-300 nm thick, 2 μm wide and about 10 μm long, were fabricated from extruded gold micro-wire and sputtered aluminum films. The obtained values, 0.45 MPa m^1/2 for gold and 0.51 MPa m^1/2 for aluminum are on the same order of those for brittle materials. Such reduction in fracture toughness is discussed in light of reduced dislocation activities in the severely work hardened gold and dislocation starved aluminum specimens.