The surface structure of CeO2(001) single crystals studied by elevated temperature STM

We have studied the atomic structure of the CeO2(001) 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(001) revealed a root2/2(3 x 2)R45 degrees surface reconstruction. Calculation confirmed oxygen in the top layer. Upon removal of further oxygen, Ce ions in the subsurface layer are reduced to Ce3+. Because oxygen from bridging positions is removed during this process the surface maintains its root2/2(3 x 2)R45 degrees 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 root2/2(3 x 2)R45 degrees 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. After reoxidation and annealing a c(3 x 3) surface reconstruction was found, LEED investigations confirmed the STM results and indicate some disorder of the surface in the [110] direction. (C) 2001 Elsevier Science B.V. All rights reserved.