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 dep endency. A dramatic topographic change was observed around 725 K, whic h is most likely due to the oxygen desorption into the gas phase and t he 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 nu cleation stage with atomic resolution. Both dimer and tetramer Pd clus ters have been observed; however no single Pd atoms were detected. The se results support the ''classical'' nucleation model which assumes th at 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 e lectronic properties of the Pd clusters have been studied to relate cl uster structure to electronic composition.