Formation and atomic structure of self-assembled Dy silicide clusters on the Si(111)7 × 7 surface

The formation and atomic structure of self-assembled Dy silicide clusters on the Si(111)7 × 7 surface are studied using scanning tunneling microscopy. We used Dy coverages in the range from 0.04 ML to 0.2 ML, substrate temperatures from room temperature to 500 °C, and two different annealing procedures, reactive deposition epitaxy and solid phase epitaxy, to investigate the growth behavior of these clusters. Depending on the preparation conditions we found the self-assembly of different cluster types. Two main types of Dy silicide clusters occurring frequently were identified: off-center clusters that form close to an edge of the half unit cell and centered clusters that appear as triangles centered within the half unit cell. Both cluster types show a strong preference for the faulted half unit cell of the 7 × 7 reconstruction. By carefully analyzing the STM images we were able to identify the atomic structure of the off-center Dy silicide clusters and to propose a structure model for the centered Dy silicide clusters, both consisting of six Dy atoms and three Si atoms.