Self-Assembly of Nanocrystalline Structures from Freestanding Oxide Membranes

We present a novel route to fabricating nanocrystalline oxide structures of exceptional quality utilizing freestanding oxide membranes. The thermally induced self-assembly of nanocrystalline structures is driven by dewetting oxide membranes once they are lifted off and transferred onto sapphire substrates. Upon annealing at temperatures below the melting point of the membranes, they self-assemble systematically into a variety of nanostructures such as nanovoids, nanowires, and nanocrystals. The orientation of the nanostructures is exactly provided by the crystal lattice of the transferred membrane. The microstructure of the nanocrystals exhibits exceptional quality, characterized by a pristine crystal structure and uniform stoichiometry, and their alignment exceeds the capabilities of lithography and ion-milling techniques. These findings illustrate the nanofabrication opportunities created by dewetting complex oxides. Furthermore, the physics underlying the self-assembly process in the membranes can potentially enhance our understanding of interface diffusion, which is important to epitaxial thin film growth.