  The influence of graphene islands on the electronic structure of the Ir(111)
surface is investigated. Scanning tunneling spectroscopy (STS) indicates the
presence of a two-dimensional electron gas with a binding energy of -160meV and
an effective mass of -0.18m_e underneath single-layer graphene on the Ir(111)
surface. Density functional calculations reveal that the STS features are
predominantly due to a holelike surface resonance of the Ir(111) substrate.
Nanometer-sized graphene islands act as local gates, which shift and confine
the surface resonance.
