Encapsulated Pd crystals on anatase supports: high precision determination of the titanate overlayer moiré structure

Palladium (Pd) crystal islands, with 100–200 nm wide (111) top facets, were grown in ultrahigh vacuum (UHV) on an anatase (001) film supported on a SrTiO3(001) substrate. Annealing the crystals at > 600 °C causes encapsulation by a TiOx monolayer due to the strong metal–support interaction (SMSI). Scanning tunneling microscopy (STM) reveals that the TiOx monolayer on the Pd(111) facets consists of two periodicities: one is a hexagonal (4 × 4)R1.5° structure, and the other is a larger-scale periodicity consisting of a two-fold symmetric pattern of dark regions that can be described by a (4√39 × 4√61)R42.4° superstructure. This double-periodicity structure requires a formation area of at least 100s of nm2. An atomic model is developed that encompasses all features of the moiré superstructure