Scanning tunneling microscopy studies of Co and Fe nanoclusters on Si(111)

Abstract

We demonstrate the growth of reactive metal Co and Fe induced magic clusters on Si(111)-(7??7). In situ scanning tunneling microscopy imaging (STM) studies show three equivalent orientations of the combined magic cluster and adatom vacancies within a half-unit cell (HUC), which is a common feature of these ferromagnetic metals on Si(111)-(7??7). The clusters are off-center in the 7??7 HUC breaking the local threefold symmetry, thereby distinguishing this system from other group-III magic clusters. Supported by first-principles total energy calculations, we propose a model to explain the atomic structure and formation mechanism of these clusters. Using scanning tunneling spectroscopy, we have further investigated the electronic structure of these clusters and observed the localization of charge at these selective cluster sites. We attempt to use these clusters for the directed assembly of C60 molecules on the 7??7 template. We also investigate Fe and Co-silicide nucleation on Si(111)-(7??7) and analyze the surface structure of atomically flat islands. Our STM study reveals the terrace width dependence on the size, shape transition, and nucleation sites of self-assembled cobalt silicide clusters on Si(111)-(7??7). The thermal decomposition of C60 on Co/Si(111) is also shown to occur at lower temperatures.