The surface structure of CeO2(0 0 1) single crystals studied by elevated temperature STM

We have studied the atomic structure of the CeO2(0 0 1) surface as an example for a polar “type III” surface by scanning tunnelling microscope (STM), low energy electron diffraction (LEED) and atomistic simulation. High resolution STM on single crystalline CeO2(0 0 1) revealed a 22(3×2)R45° surface reconstruction. Calculation confirmed oxygen in the top layer. Upon removal of further oxygen, Ce4+ ions in the subsurface layer are reduced to Ce3+. Because oxygen from bridging positions is removed during this process the surface maintains its 22(3×2)R45° reconstruction. Atomistic modelling showed that an arrangement of Ce3+ ions in lines is energetically favourable compared to other structures. Among a number of surfaces considered the 22(3×2)R45° reconstruction was energetically most favoured. These results confirm the experimental findings and show that polar “type III” surfaces in metal oxides reduce their surface energy by reconstruction. reoxidation and annealing a c(3×3) surface reconstruction was found. LEED investigations confirmed the STM results and indicate some disorder of the surface in the [1 1 0] direction.