Above and Below Graphene: Nanoparticle Chemistry and Interface Reactions

Abstract: The work presented in this dissertation addresses two main topics: (i) graphene supported nanoparticles and their stability upon gas adsorption, and (ii) intercalation of different molecules under graphene and their reactions under graphene. From an interplay of X-ray photoelectron spectroscopy, scanning tunneling microscopy, low energy electron diffraction, and density functional theory an atomic scale understanding of both the nanoparticles and the intercalated structures is obtained. Growing very well ordered arrays of metal nanoparticles on Ir(111) supported graphene it is shown that the nanoparticles bind to the graphene through rehybridisation of the C-atoms in graphene from sp2 to sp3, below and in the vicinity of the nanoparticles. Further, the stability of the nanoparticles in CO is studied as a function of their size, and it is revealed that small nanoparticles sinter already at very low CO pressures. This instability limits the potential of graphene supported nanoparticles for catalytic reactions involving CO. Future research could be aimed at improving the stability of these nanoparticles. Intercalation of molecules between graphene and its substrate is a research topic driven mainly by the possibility to tune the electronic structure of graphene by intercalation and by the possibility to study reactions in the confined space between graphene and its substrate. In my studies of the intercalation of oxygen, hydrogen and carbon monoxide under graphene the edges are identified to provide a barrier for intercalation. Further, the atomic structures formed by the intercalated molecules, and the spectroscopic fingerprint of graphene of each structure is determined. Using the knowledge of the intercalated structures water formation and trapping under graphene is studied and it is found that a super-dense structure of hydroxyl groups and water is formed under graphene. Thus, the interface between graphene and the reactive substrate can be used for performing reactions, and stabilizing and characterizing the products.