Spontaneous formation of ordered nanocrystal arrays in films evaporated onto nanopore array substrates

We have investigated the structure of films thermally evaporated onto anodic aluminum oxide substrates that are patterned with a hexagonal array of 34 and 80 nm diameter holes spaced by 100 nm. Over a range of film thicknesses, Pb and Sn films spontaneously self-assemble into an array of nanocrystals in registry with the underlying hole lattice. The development of the arrays with thickness indicates that surface energies drive coalescing grains to move over the holes. Materials that wet the substrate (Pd, Ge) or whose grains do not coalesce at the substrate temperature (Au) do not form arrays. Potential applications are discussed. (C) 2005 American Institute of Physics.