Nonequilibrium Interface Dynamics:
Fundamental Physical Issues in Nonequilibrium Interface Dynamics

CSIC Building (#406), Seminar Room 4122.
Directions: home.cscamm.umd.edu/directions

Spinodal Decomposition in 'Curved Space' and Nanoporosity Formation

Dr. Alain Karma

Physics Department at Northeastern University

Abstract:   Dealloying is a method for fabricating open nanoporous structures with ligament widths as small as a few nanometers, useful for sensor and other applications that require ultra-high surface area materials. In the context of silver-gold alloys, it was recently proposed that the formation of these structures is due to a phase separation process that produces gold-rich and gold-poor regions at the curved alloy-electrolyte interface [J. Erlebacher, M. J. Aziz, A. Karma, N. Dimitrov, and K. Sieradzki, Nature 410, 450 (2001)]. Here, we explore this idea further using a phase-field approach where the alloy-electrolyte interface is spatially diffuse. The model leaves out most of the details of the electrochemistry of the dealloying process, but describes simultaneously the kinetics of quasi-two-dimensional spinodal decomposition confined to a moving interface of complex shape, and the highly nonlinear motion of this interface that is itself governed by the local (gold) composition and the interface curvature. Despite its simplicity, this model is able to reproduce qualitatively several salient features of nanoporosity formation observed experimentally including the existence of a threshold over-potential for porosity formation and its dependence on alloy composition. These results shed light on the origin of this threshold and the physical parameters that govern the pore scale.