Effect of the dislocation emergence on the mechanical behavior of coated materials: Elastic energy relaxation or adhesion modification

Nickel thin films of various thicknesses deposited on lithium fluoride single crystals have been strained to study the effect of steps on the buckling phenomenon. In these experiments, the nanometer-scale steps result from the emergence process of dislocations coming from the substrate and piling-up at the film/substrate interface. The coated specimens were investigated by in situ atomic force microscopy. It is shown that the buckling phenomenon preferentially occurs just above the step structures in compression tests, while no buckling takes place in tension. From elastic energy consideration, it is concluded that the main effect of substrate plasticity is to strongly modify the critical stress for buckling, with no significant result on the adhesion properties.