Geometry control of size selected Pt clusters bound to Si substrate surface by cluster impact deposition.

Abstract

Geometry of platinum clusters, PtN (N = 30-71), supported on a silicon substrate was investigated, aiming to control the geometry. The supported clusters were prepared by the impact of size-selected PtN + onto the substrate at a given collision energy (cluster-impact deposition), and their geometry was observed by means of a scanning-tunneling microscope. Even at the collision energy of 1 eV per Pt atom, sufficiently strong Pt-Si interaction between PtN (N = 30 and 45) and the Si substrate allows them to be supported as close-packed monatomic-layered Pt disks, while at N = 60, multilayered shapes exist besides the monatomic-layered shape, the fraction of which increases at N = 71. When the collision energy is increased, Si atoms located at the interface between the cluster and Si substrate dissolve into the cluster, and with further increase in the collision energy, the Pt-Si cluster is partially implanted into the substrate. The transition in the shape of the supported clusters with the collision energy and the cluster size was explained according to the deformation of the clusters and the substrate surface by the cluster impact. It is proposed that the momentum of PtN + per its cross section is a good index to control the geometry in the case of strong cluster-support interaction such as Pt and Si.