Terbium induced nanostructures on Si(111)

The growth of self-assembled Tb induced nanostructures on the Si(111) surface is investigated using scanning tunneling microscopy. Depending on the growth conditions, three regimes are identified in which different types of nanostructures appear. At very low Tb coverages and moderate growth temperatures, the 7 x 7 periodicity of the Si(111) surface remains intact and magic clusters form within single 7 x 7 half unit cells. In the intermediate regime of Tb coverages below one monolayer, the formation of different superstructures is observed. Here, a chain-like 5 x 2 superstructure, a 2 root 3 x 2 root 3 R30 degrees superstructure, and elongated islands showing a 2 x 1 reconstruction on top are found. From a detailed study of the 5 x 2 superstructure it is demonstrated that it consists of alternating Si Seiwatz and Si honeycomb chains with rows of Tb atoms in the channels in between. Moreover, registry shifts between the Tb rows lead to different configurations of this superstructure. At coverages exceeding one monolayer, the growth of islands of two-dimensional TbSi2 monolayers and three-dimensional Tb3Si5 multilayers dominates. (C) 2015 Elsevier B.V. All rights reserved.