Tracking the emergence of epitaxial metal–oxide interfaces from precursor alloys

Heterointerfaces with an epitaxial relationship, self-assembled nanocomposites of Pt(111)/CeO₂(111) 60°, were successfully formed by simple oxidation of Pt₅Ce alloy. Oxygen dissolution into the alloy causes spacial periodic compositional perturbation by atomic segregation, specifically, by local diffusion of Pt and Ce atoms. A striped pattern of Pt and CeO₂ with a 4-5 nm periodicity formed through phase transformation of the Pt-rich alloy and oxidation of the Ce-rich alloy, respectively. Notably, a fully epitaxial relationship between the Pt and CeO₂ phases was observed even in the initial stage. With continued annealing, the crystals rotated into an energetically favorable orientation with respect to the remaining (111)Pt//(111)CeO₂. The alloy oxidation and its resulting nanoscale phase-separation behavior were verified in an ex situ annealing experiment of an alloy specimen, which had been first thinned by a focused ion beam. Changing the oxygen partial pressure to the reaction interface may alter the orientation relationship between the hexagonal close-packed Pt₅Ce structure and face-centered cubic Pt/CeO₂ structure, thereby altering the growth direction of the separated phases. These findings present a pathway for the self-assembly of epitaxial Pt(111)/CeO₂(111) interface and are expected to assist the structural design of metal-oxide nanocomposites.