Atomic Structure and Electronic Properties of Self-Assembled Clusters on Silicon Surfaces

In this thesis, the growth, the atomic structure as well as the electronic properties of self-assembled magic clusters and of thin rare earth silicide films on Si surfaces are investigated using scanning tunneling microscopy and spectroscopy. Self-assembled magic clusters on surfaces are promising structures to utilize the fascinating properties of clusters as zero-dimensional nanoobjects in future applications, e.g. in high density memory devices or in catalysis. For Sb on the Si(111)7×7 surface, the growth of pure Si clusters as well as of so-called Sb ringlike clusters is observed. The latter are found to exhibit different stoichiometries within the same basic structure by replacing Si atoms by Sb atoms, influencing strongly their electronic properties. The widely studied magic In and Ga clusters on Si(111) are used as a model system to study the detailed charge redistribution that takes place on the surface during the cluster formation as well as the effects of cluster accumulation on the electronic properties. In addition, the Si(557) surface, which is vicinal to Si(111), is used as a template to enable the growth of one-dimensional chains of magic clusters. Nanostructures induced by the rare earth metals Tb and Dy on Si surfaces are the material system most comprehensively studied in this thesis. For Dy and Tb on Si(111), the same two types of magic clusters are observed, which is related to the chemical similarity of the trivalent rare earth metals. These are the so-called off-center rare earth silicide cluster and the centered rare earth silicide clusters, for which the atomic structure could be identified and a semiconducting behavior is found by scanning tunneling spectroscopy. Moreover, the centered rare earth silicide clusters show a switching between two stable configurations. On the Si(001)2×1 surface, a completely different growth behavior is observed. Here, also magic Dy silicide clusters form, but the clusters show a one-dimensional ordering and assemble into chains consisting of different numbers of magic clusters. The thin film growth of Tb on Si(111) shows many similarities with the growth behavior observed for other trivalent rare earth metals in this parameter regime. For submonolayer Tb coverages, a 2"the square root of"3×2"the square root of"3 R30° superstructure, a 5×2 superstructure as well as nanorods showing either a 2×1 or a 4×1 superstructure on top are observed. For the 5×2 superstructure an existing structure model is refined and a detailed investigation is derived on how registry shifts lead to the different configurations of this structure. In the monolayer-to-multilayer regime, the growth of the TbSi2 monolayer with 1×1 periodicity and of the Tb3Si5 multilayer with "the square root of"3×"the square root of"3 R30° periodicity is found