Oligoethylene-bridged diferrocene on Ag(110): Monolayer structures and adsorbate-induced faceting

Zhong DY, Wang WC, Dou RF, Wedeking K, Erker G, Chi LF, Fuchs H

Abstract

The self-assembly of a ferrocene (Fc) derivative, oligoethylene-bridged diferrocene (diFc), Fc(CH2)(14)Fc, on Ag(110) surface has been investigated by scanning tunneling microscopy (STM) under ultrahigh vacuum. Three ordered structures, the majority beta and the minorities alpha and gamma, are formed at monolayer coverage. In alpha and gamma, a unit cell contains one molecule and the molecules are parallel to each other so that the distances between Fc groups and between oligoethylene chains are reduced. A unit cell contains five molecules in beta: four of them are parallel to each other but not parallel to the fifth. The interaction between diFc and Ag(110), which is relatively strong in comparison to the intermolecular interaction, is dominant for the assembly of the ordered structures. The adsorption of diFc molecules induces the reorganization of substrate steps, which prefer to follow the directions of the superstructure lattice vectors, i.e., (-/+ 1,2) and (+/- 3,2) of the Ag(110) surface. The (12 13-1) facet is formed due to step bunching at regions with high step density. By using in situ STM, the process of step reorganization and faceting has been observed in real time. It is concluded that the Ag adatoms play a key role on the substrate reorganization.