Measuring the interface stress: Silver/nickel interfaces

Interface stress is a surface thermodynamics quantity associated with the r eversible work of elastically straining an internal solid interface. In a m ultilayered thin film, the combined effect of the interface stress of each interface results in an in-plane biaxial volume stress acting within the la yers of the film that is inversely proportional to the bilayer thickness. W e calculated the interface stress of an interface between {111} textured Ag and Ni on the basis of direct measurements of the dependence of the in-pla ne elastic strains on the bilayer thickness. The strains were obtained usin g transmission x-ray diffraction. Unlike previous studies of this type, we used freestanding films so that there was no need to correct for intrinsic stresses resulting from forces applied by the substrate that can lead to la rge uncertainties of the calculated interface stress value. Based on the la ttice parameters of the bulk, pure elements, an interface stress of -2.02 /- 0.26 N/m was calculated using the x-ray diffraction results from films w ith bilayer thicknesses greater than 5 nm. This value is somewhat smaller t han previous measurements obtained from as-deposited films supported by sub strates. For smaller bilayer thicknesses the apparent interface stress beco mes smaller in magnitude, possibly due to a loss of layering in the specime ns.