SUPERSTRUCTURES AND DEFECT STRUCTURES REVEALED BY ATOMIC-SCALE STM IMAGING OF WO3(001)

Atomic-scale images of the (001) surface of monoclinic WO3 have been obtained by scanning tunneling microscopy. Termination of the surface WO2 plane with half a monolayer of oxygen ions gives a surface periodicity root 2 times that of the underlying ReO3-like framework. An additional periodicity is introduced by tilting of WO6 octahedra to produce alternately long and short O-O separations along the [110] direction. This produces a (2 X 2) superstructure approximating the space group c2mm. Prominent defect lines at the surface are attributed to missing oxygen ions.