Dokument

Summary:
In this cumulative dissertation organic-inorganic hybrid interfaces with relevance for nanoelectronic applications are investigated with theoretical methods. An emphasis is put on the elucidation of interface reaction mechanisms and the employment of bonding analysis to better inform synthetic design choices. Furthermore, electronic structure related properties are calculated in order to explain experimental observations. The dissertation is organized in two parts. In the first part, the covalent attachment of organic layers on the (001) facet of the inorganic semiconductor silicon is studied. The second part is concerned with the creation of interface models for organic semiconductors on Ag(111). In the past it was shown that cyclooctyne is a particularly suitable platform molecule for the purpose of creating a contact layer with Si(001) due to its highly selective adsoption. Building on this prior work, the focus of this dissertation is hence the growth of a second layer on the contact layer. For this purpose, promising reactions schemes with “click”-characteristics (fast, excellent yield, solvent tolerant) are studied. These are the azide-alkyne cycloaddition (AAC), the enolether-tetrazine inverse electron demand Diels-Alder reaction (IEDDA) as well as the nucleophilic substitutions of an acid chloride mediated esterification (ACE) and the sulfonylfluoride exchange (SuFEx). The second main topic of this dissertation is the chemical interplay of the Ag(111) surface with nature inspired organic semiconductors based on pyrrole units. In comparison to silicon, the coinage metal surface has a comparatively low reactivity. This property is crucial for keeping the π-systems of the organic semiconductors intact after interface formation. Still, various bonding patterns can emerge at the interface. Besides van der Waals interactions, an exchange of electron density between the surface and the organic π-system is observed. The strength of this interaction is determined primarily by the frontier orbitals of the molecule. In summary, the collected work of this dissertation shows that quantum chemical methods are a valuable tool for better understanding the chemistry and electronic structure of hybrid interfaces. Insights gained from theory not only explain experimental observations but can also be used to guide synthetic efforts even though, different terminologies and concepts exist for metal and semiconductor surfaces. Furthermore, the studies presented here highlight that various types of interfaces can be described efficiently within an ab inito framework.

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