TUNING THE ELECTRONIC AND SPINTRONIC PROPERTIES OF GRAPHENE BY DOPING AND ATOM ADSORPTION

Abstract

The work described in this thesis reports on the possibilities of tuning the electronic and spintronic properties of graphene by doping and atom adsorption. Novel experimental and theoretical results are presented, showing how deeply graphene properties can be transformed. In a first part, we study graphene doped to ultra-high charge carrier density regimes by means of a polymer-electrolyte gating technique. We show how the temperature-dependence of the resistivity is affected by large Fermi energies. Possible implications for intrinsic superconductivity in graphene are discussed. In a second part, we show how graphene, a very good conductor in its pristine form, can be turned into a granular metal by chemical functionalization. We report the observation of multiple inelastic and elastic co-tunneling conduction mechanisms such granular graphene systems, fabricated by hydrogenation of free-standing graphene sheets. Even though multiple inelastic co-tunneling has already been observed in conventional granular metals, this is, to the best of our knowledge, the first time multiple elastic co-tunneling is observed. These conduction mechanisms comprising series of virtual tunneling events, show deviations from established theories. However, they are consistent with a theory developed for granular Dirac materials, and presented in this thesis. Finally, we theoretically study the modifications of graphene¿s spintronic properties by atom adsorption. We show that atoms adsorbed in hollow position can lead to the appearance of strong and gate-tunable Spin Hall Effect, while certain atoms adsorbed on graphene in top-position can induce a large Anomalous Hall Effect.