Scanning tunneling microscopy studies of the TiO2(110) surface: Structure and the nucleation growth of Pd

The surface structure of TiO2(110) has been reexamined using scanning tunneling microscopy (STM), especially in terms of its temperature dependency. A dramatic topographic change was observed around 725 K, which is most likely due to the oxygen desorption into the gas phase and the simultaneous diffusion of Ti into the bulk. The atomically resolved STM images show a strong dependency on the tip composition and allow a double-bridging oxygen vacancy to be identified. The nucleation and growth of Pd on the TiO2(110) surface have also been studied at the nucleation stage with atomic resolution. Both dimer and tetramer Pd clusters have been observed; however no single Pd atoms were detected. These results support the ''classical'' nucleation model which assumes that only monomers an mobile, whereas dimers are stable nuclei. A marked preferential nucleation and growth of Pd clusters at step edges have also been observed. In addition to topographic structures, the local electronic properties of the Pd clusters have been studied to relate cluster structure to electronic composition.