Structural and electronic properties of the Co-induced Si(111) surface reconstruction

Scanning Tunneling Microscopy (STM) observations of the Si(111) 13 × 13 − R 13.9 ° -Co surface reconstruction show that two types of clusters coexist on the surface appearing as dark and bright on the images. The atomic structure of the dark ones has been recently proposed by L. Chaput et al. (L. Chaput, F. Dulot, M. C. Hanf, P. Wetzel, Surf. Sci. 604 (2010) 513) [34]. We found that each dark cluster consists of three Co atoms located on substitutional sites of the Si(111) surface with an overlying triangle of six Si adatoms. Here, we present the determination of the bright clusters atomic structure. Combining high-resolution filled and empty-state STM images and DFT simulations, we show that bright clusters consist of additional Si adatoms located on top of the six Si atoms terminating the dark clusters. These Si adatoms are in number of one, two or three. Energy stability of these three configurations and description of the electronic states are discussed in detail.