Atomic-resolution imaging of size-selected platinum clusters on TiO(2)(110) surfaces.

Size-selected Pt(n) (n=4,7-10,15) clusters were deposited on TiO(2)(110)-(1x1) surfaces and imaged at atomic resolution using an ultrahigh-vacuum scanning tunneling microscope with a carbon nanotube tip. Clusters smaller than Pt(7) lay flat on the surface with a planar structure and a planar-to-three-dimensional transition occurred at n=8 for Pt(n) clusters on TiO(2). However, both Pt(8) and Pt(9) had two types of geometric structures. The geometric structures depend strongly on the number of atoms in the deposited cluster possibly because of the differences in binding energies in different-sized clusters and different degrees of interaction with the surface. We obtained atomic-resolution images of size-selected clusters on surfaces for the first time, enabling the identification of atomic alignments in the clusters on the surface.