Theoretical investigation of nanoscale solid state and cluster structures on surfaces

Abstract

In this thesis, density functional theory was applied to three systems related to nanostructures and clusters: hydrogenated gold clusters, deposited Si4 clusters and self-assembled monolayers on gold surfaces. In the first part, hydrogenated gold clusters in the gas phase are studied up to a cluster size of seven atoms. The structure of several isomers for each cluster size was calculated and compared to experimental data from photodetachment experiments. This procedure allowed the identification of the isomer that is present in the cluster experiment. In the second part of this work, the eligibility of Si4 clusters deposited onto different substrates was studied. The focus was on whether Si4 clusters on a surface remain as individual species or, less desirably, coagulate to Si8. The computational approach as applied in the last part of the thesis goes beyond the standard DFT scheme used in the rest of the thesis. In order to study self-assembled monolayers formed by adsorption of alkanethiol chains on a Au(111) surface, it was necessary to introduce additional classical interactions. Using this so-called 'hybrid approach', the long-lasting debate about the adsorption state of sulfur on the gold surface was investigated. Despite great experimental effort it is still unclear if upon adsorption a sulfur-sulfur bond is formed as suggested in the so-called 'disulfide model' or if the chains adsorb as thiolates without formation of an S-S bond ('thiolate model').