Effect of applied stress tensor anisotropy on the electromechanically driven complex dynamics of void surfaces in metallic thin films.

We present a systematic computational analysis of the complex, electromechanically driven surface dynamics of voids in thin films of face-centered cubic metals for <100>-oriented film planes characterized by four-fold symmetry of surface diffusional anisotropy. The voids are located at an edge of the metallic thin film, and the film is subjected simultaneously to an external electric field and an anisotropic biaxial tensile stress. Our analysis is based on self-consistent dynamical simulations of driven void surface morphological response according to a well-validated, two-dimensional, and fully nonlinear model. We examine thoroughly the effects of the anisotropic mechanical loading on the morphological evolution of the electromigration-driven void surface and the resulting asymptotic states of the surface morphological response. We have found supercritical Hopf-bifurcation transitions from stable steady to stable time-periodic states. For such films and over the range of electromechanical conditions examined, the only possible stable asymptotic states are either time-periodic states characterized by a single period of oscillation or steady states without any change in the void shape. We have determined the stability domain boundaries of the various asymptotic states and their dependence on the anisotropy of the applied stress tensor. The loading anisotropy has significant effects on the stability domain boundaries, but it does not introduce any more complex void dynamics in <100>-oriented films than that under isotropic mechanical loading. [ABSTRACT FROM AUTHOR]