A method for forming a metal/metal oxide structure that includes forming metal oxide regions, e.g., ruthenium oxide regions, at grain boundaries of a metal layer, e.g., platinum. Preferably, the metal oxide regions are formed by diffusion of oxygen through grain boundaries of the metal layer, e.g., platinum, to oxidize a metal layer thereon, e.g., ruthenium layer. The structure is particularly advantageous for use in capacitor structures and memory devices, such as dynamic random access memory (DRAM) devices.