Structure and apparent topography of TiO2(110) surfaces

We present self-consistent ab initio total-energy and electronic-structure calculations on stoichiometric and nonstoichiometric TiO2(110) surfaces. Scanning tunneling microscopy (STM) topographs are simulated by calculating the local electronic density of states over an energy window appropriate for the experimental positive-bias conditions. We find that under these conditions the STM tends to image the undercoordinated Ti atoms, in spite of the physical protrusion of the O atoms, giving an apparent reversal of topographic contrast on the stoichiometric 1 x 1 or missing-row 2 X 1 surface. We also show that both the interpretation of STM images and the direct comparison of surface energies favor an added-row structure over the missing-row structure for the oxygen-deficient 2 X 1 surface. [S0163-1829(97)04840-6].