Ordered structures of calcium oxide on TiO2(110) studied by STM and atomistic simulation

A well-ordered surface layer of Ca on TiO2(110) has been prepared by forcing Ca impurities from the bulk to segregate to the surface during annealing, The surface was studied by scanning tunneling microscopy (STM), Auger electron spectroscopy, low-energy electron diffraction, reflection high-energy electron diffraction, and atomistic simulation. Calcium forms a p(3 X 1) reconstruction. The reconstructed areas extend well beyond the scanning range of the STM. Calculations have shown that calcium in TiO2 will segregate to the surface to occupy the positions of the fivefold coordinated Ti ions. Ordering is energetically favorable with the p(3X1) reconstruction lowest in energy. Calcium is sitting on top of the surface. It is concluded that the STM contrast is strongly influenced by geometric effects. [S0163-1829(99)12515-3].