Effect of noble-metal contacts on doping and band gap of graphene

Density-functional theory of graphene predicts that noble-metal contacts will provide doping but leave the Dirac crossing point intact. We use high-resolution angle-resolved photoemission and noble-metal intercalation to show that, instead, substantial band gaps open in proportion to the doping effect. Graphene on Au, however, remains gapless even during heavy electron doping by adsorbed Gd. A key role is assigned to quantum interference at the almost incommensurate graphene/Au interface.