(13×13)R13.9° reconstruction of the Co-Si(1 1 1) surface investigated by high-resolution STM and DFT calculations

The Co-Si(1 1 1) (13×13)R13.9° surface reconstruction induced by deposition of submonolayer of Co and subsequent annealing has been investigated combining scanning tunnelling microscopy (STM) and ab-initio calculations. High-resolution STM images reveal that two sorts of clusters coexist within each (13×13)R13.9° domain. Based on the STM results a model is proposed to account for the (13×13)R13.9° reconstruction. Each cluster consists of three Co atoms located on substitutional sites of the Si(1 1 1) surface. For one type of clusters, appearing as dark on the STM images, the Co is lying under one layer of six Si adatoms. In contrast, for the second kind of clusters, which exhibit a bright appearance, three additional Si atoms are present above the triangle formed by the six Si. The model for the dark clusters is validated by theoretical calculations.