Self-assembled molecular nanostructures on graphene vs metallic substrate: structural and electronic properties

Self-assembled organic molecules, that is, molecules that spontaneously assemble into ordered structures without outside forces, are a class of materials with potential applications in electronics, photovoltaics and catalysis. Interactions at the molecule substrate interface are crucial to the performance of films of organic molecules in such applications, as these interactions are influential on both the film’s structural and electronic properties. To this end we study these interface interactions as laid out in this thesis. Chapters 4 and 5 treat the study of a molecular electron donor on graphene on Ir(111) (chapter 4) and Ni(111) (chapter 5). In both cases, the molecules form an epitaxial layer, i.e. the self-assembled molecular layer is commensurate with the graphene substrate. Study of the electronic properties of the molecular layer shows no signs of chemisorption of charge transfer, thus leaving only weak interactions to control the molecule-substrate interface. Commensurate overlayers are usually only found alongside strong interface interactions, so in chapter 5 we discuss the properties of the molecule-graphene interface that might facilitate a commensurate structure alongside weak interface interactions. In chapter 6 we report on the study of a two-dimensional metal-organic coordination network composed of a functionalised cobalt porphyrin and additional cobalt atoms on two substrates: Au(111) and graphene on Ir(111). We show that graphene acts as a decoupling layer by preventing the cobalt porphyrin-substrate interaction.