Ripples and charge puddles in screened graphene
Résumé
At vanishing charge carrier density, graphene on a dielectric substrate exhibits spatial doping inhomogeneities forming electron-hole puddles. Understanding and controlling the latter is of crucial importance for unraveling many of graphene's fundamental properties at the Dirac point, where the linear valence and conduction bands meet. Charged impurities trapped in the dielectric substrate as well as the local graphene curvature have been pointed to as the puddles' origin. Here we show by scanning tunneling microscopy/spectroscopy the coexistence and correlation of charge puddles and topographic ripples in graphene decoupled from a metallic Ir substrate. The perfect screening of charged impurities by the metallic substrate reveals charge puddles directly induced by the local graphene-substrate distance and the ensuing charge transfer. Furthermore, the analysis of Dirac fermion interferences shows that electron-electron interactions are also strongly screened. Our findings therefore demonstrate that graphene on Ir provides a new platform to study the non-interacting limit for massless Dirac electrons in graphene.