The effect of stoichiometry on the stability of steps on TiO2(1 1 0)

The equilibrium composition of titanium oxide depends on temperature and partial oxygen pressure. Deviations from the TiO2 stoichiometry cause changes in colour and an increase in electrical conductivity. In this study we use ex situ atomic force microscopy observations to show that changes in stoichiometry also affect the morphology of steps on the TiO2(1 1 0) surface. Upon annealing of a sputtered stoichiometric surface at 1135 K, first hexagonal islands are formed. During further annealing these hexagonal shapes do not simply grow in size. Instead elongated structures form along the [0 0 1] direction, and the surface tends to maximize the length of the [0 0 1] steps. We propose that the formation of a [0 0 1] step allows the surface to make a non-stoichiometric structure without destroying the crystal structure.