Self-Ordering Behavior on Patterned Model Surfaces

We use computer simulation to explore phenomena which could be used to grow arbitrary arrangements of nanostructures on metal surfaces via the vacuum deposition process. The method involves a three-stage process where, in the first "pattern formation stage", a desired pattern of adatom islands is created on a base metal substrate, followed by a second "fixing stage" where an immiscible metallic species is vacuum deposited on the substrate at elevated temperatures to fill vacancy islands, and a final "growth stage" involving the further vacuum deposition of specific metal or nonmetal atomic species. In this work, we use molecular,dynamic (MD) simulations to study the self-ordering behavior in the "fixing" and "growth" stage of assembly. We use the model immiscible systems Pt/Ag and Pt/Au with Pt as the base substrate. It was observed in the "fixing" stage that immiscible species deposited at higher temperatures would readily move off substrate adatom islands effectively "flooding" the vacancy areas around the islands, eventually forming a structurally stable, atomically smooth surface of alternating atomic species. In the "growth" stage, substrate species deposited at lower temperatures on such patterned surfaces were observed to preferentially move off surface regions covered by the immiscible species and onto the original adatom island areas, sometimes aggregating into nanostructures several atomic layers high.