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 degrees 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 x 4)R1.5 degrees 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 root 39 x 4 root 61)R42.4 degrees superstructure. This double periodicity structure requires a formation area of at least 100s of nm(2). An atomic model is developed that encompasses all features of the moire superstructure.