Interaction of magnetic and non-magnetic metals with graphene

This thesis deals with an investigation of the electronic properties of six examples of graphene-metal interfaces. Such systems are of great current interest, not only from a fundamental point of view, but also with respect to possible applications in electronic devices and other fields. The (111) surface of iridium is used as a template for graphene growth, in view of the weak interaction between the partners, and due to the excellent structural quality. After a brief introduction (chapter 1), the properties of graphene and the graphene/Ir(111) interface are described in chapter 2. My main experimental method within the thesis is photoemission and -absorption, hence chapter 3 deals with the underlying physics. The data analysis procedures are explained in chapter 5. The experimental stations on which the work was performed are described in chapter 4, including a state-of-the-art laboratory station that was built up within the work on this thesis. Chapters 6 through 10 then report on my findings for graphene on bulk and intercalated metals in between graphene and Ir(111), starting with Ir(111) in chapter 6. Intercalated copper layers are dealt with in chapter 7, a particularly important example since the signatures of hybridization between metal states and the graphene π band are especially clear, and the mechanism of band gap opening can be explained in detail on the basis of DFT calculations. Electronic and magnetic structure investigations for intercalated cobalt layers are covered in chapter 8. The transfer of magnetic moment onto the formerly paramagnetic graphene π states is evident from x-ray magnetic circular dichroism measurements at the carbon K edge. The emergence of ferromagnetic ordering in the cobalt films is reported and analyzed by recourse to theory. Intercalated ytterbium (chapter 9) is found to exhibit similarities with copper, since in both cases the region near the Fermi level is exclusively occupied by s-p-type states. Like in copper, hybridization between metal and graphene states can be clearly observed. Finally, the case of intercalated manganese is a special one: d-states are found to interact with graphene, but they do not seem to have the detrimental effect on the Dirac cone as observed for nickel and cobalt in chapter 8. Altogether, a consistent overview of metal-graphene interface electronic structure is given.