Scanning tunneling microscopy at multiple voltage biases of stable "ring-like" Ag clusters on Si(111)-(7×\times7)

Since more than twenty years it is known that deposition of Ag onto Si(111)-(7\times7) leads under certain conditions to the formation of so-called "ring-like" clusters, that are particularly stable among small clusters. In order to resolve their still unknown atomic structure, we performed voltage dependent scanning tunneling microscopy (STM) measurements providing interesting information about the electronic properties of clusters which are linked with their atomic structure. Based on a structural model of Au cluster on Si(111)-(7\times7) and our STM images, we propose an atomic arrangement for the two most stable Ag "ring-like" clusters.Comment: 9 pages and 5 figure

Chalcogenide-based van der Waals epitaxy: Interface conductivity of tellurium on Si(111)

We present a combined experimental and theoretical analysis of a Te rich interface layer which represents a template for chalcogenide-based van der Waals epitaxy on Si(111). On a clean Si(111)-(1×1) surface, we find Te to form a Te/Si(111)-(1×1) reconstruction to saturate the substrate bonds. A problem arising is that such an interface layer can potentially be highly conductive, undermining the applicability of the on-top grown films in electric devices. We perform here a detailed structural analysis of the pristine Te termination and present direct measurements of its electrical conductivity by in situ distance-dependent four-probe measurements. The experimental results are analyzed with respect to density functional theory calculations and the implications of the interface termination with respect to the electrical conductivity of chalcogenide-based topological insulator thin films are discussed. In detail, we find a Te/Si(111)-(1×1) interface conductivity of σTe2D=2.6(5)×10−7S/□, which is small compared to the typical conductivity of topological surface states