Pinch-off maps for the design of morphologically stable multilayer thin films with immiscible phases

Design maps are developed for the time to pinch-off via grain boundary grooving in multilayer thin films consisting of two immiscible phases. Variables include the (isotropic) interfacial/grain boundary energies, interfacial diffusivities, initial grain aspect ratio, and imposed in-plane strain rate. The maps are based on a new 2D analysis of grooving in multilayer thin films that extends earlier work by Thouless [Thouless MD. Acta Metall Mater 1993;41:1057] for single phase films. A modified Mullins [Mullins WW, J Appl Phys 1957;28:333] parameter Bmulti and time scale (tau)multi are found to control grooving kinetics, with initial groove depth scaling as t1/4, t3/4, or t, depending on the magnitude of in-plane strain rate and geometry. The maps predict that nano-scale films may or may not be more unstable to pinch-off at elevated temperature compared to micro-scale counterparts, depending on morphology, interfacial/grain boundary energies, and in-plane strain rate.