Fracture behavior and adhesion energy of nanostructured Cu/Mo multilayer films

The fracture behavior and interfacial adhesion of Cu/Mo nanostructured multilayer films (NMFs) are systematically investigated as a function of modulation period λ. A fracture mode transition from opening to shear has been reported as λ decreases from 250nm to 10nm, which is related to the constraining effect of ductile Cu layers on microcrack-initiating Mo layers. Within the λ regime below a critical size (_{λc r i}) of ~50nm, a λ-independent adhesion energy of about 2.8Jm^-2 has been determined. Within the λ regime greater than _{λc r i}, however, the measured adhesion energy increases with increasing λ. The λ dependence of evaluated adhesion energy is discussed according to the size-dependent deformation mechanism. A micromechanics model has been utilized to quantify the _{λc r i}, where the deformation mechanism is transited from dislocation pileup to confined layer slip.