Controlling Heteroepitaxy by Oxygen Chemical Potential: Exclusive Growth of (100) Oriented Ceria Nanostructures on Cu(111)

A novel and simple method is presented for the preparation of a well-defined CeO<sub>2</sub>(100) model system on Cu(111) based on the adjustment of the Ce/O ratio during growth. The method yields micrometer-sized, several nanometers high, single-phase CeO<sub>2</sub>(100) islands with controllable size and surface termination that can be benchmarked against the known (111) nanostructured islands on Cu(111). Furthermore, we demonstrate the ability to adjust the Ce to O stoichiometry from CeO<sub>2</sub>(100) (100% Ce<sup>4+</sup>) to c-Ce<sub>2</sub>O<sub>3</sub>(100) (100% Ce<sup>3+</sup>), which can be readily recognized by characteristic surface reconstructions observed by low-energy electron diffraction. The discovery of the highly stable CeO<sub><i>x</i></sub>(100) phase on a hexagonally close packed metal surface represents an unexpected growth mechanism of ceria on Cu(111), and it provides novel opportunities to prepare more elaborate models, benchmark surface chemical reactivity, and thus gain valuable insights into the redox chemistry of ceria in catalytic processes.