Role of Dangling Bond State Occupancy in Adsorption of Copper Phthalocyanine on Si(111)-Sn-root 3 x root 3
Abstract
Interaction of organic molecules with solid surfaces reflects the local electronic structure of nonequivalent surface sites. The Si(111)-Sn-root 3 x root 3 surface with intrinsic defects offers dangling bonds with various electron occupancies.
In this study, we report on the interaction of copper phthalocyanine with this surface studied with scanning tunneling microscopy and spectroscopy. Sn atoms in the adlayer contain unpaired electrons in their dangling bonds.
The molecules are found to adsorb on Sb and Si substitutional defects instead of the homogenous Sn areas. The symmetry of the molecules is lowered or lost after adsorption, and we find substantial differences in the electronic structure of the molecules adsorbed on either type of defects.
Furthermore, the molecules preferentially adsorb on double Si substitutional defects where they can switch between a static and a fuzzy state, for both of which a corresponding bonding model is proposed. Our study shows a pivotal role of substitutional defects in the reactivity of the Si(111)-Sn-root 3 x root 3 surface for the copper phthalocyanine molecules, which we attribute to local changes of electronic structure and discuss it in terms of dangling bond state occupancy.