No abstract

One leading question for the application of graphene in nanoelectronics is how electronic properties depend on the size at the nanoscale. Direct observation of the quantized electronic states is central to conveying the relationship between electronic structures and local geometry. Scanning tunneling spectroscopy was used to measure differential conductance dI/dV patterns of nanometer-size graphene islands on an Ir(111) surface. Energy-resolved dI/dV maps clearly show a spatial modulation, indicating a modulated local density of states due to quantum confinement, which is unaffected by the edge configuration. We establish the energy dispersion relation with the quantized electron wave vector obtained from a Fourier analysis of dI/dV maps. The nanoislands preserve the Dirac Fermion properties with a reduced Fermi velocity.

We performed scanning tunneling microscopy/spectroscopy (STM/S) on the edges of monolayer graphene islands grown on Ir(111). Constant current STM images reveal that the atomic corrugation at the graphene edges correlates with the moiré pattern of graphene on Ir(111). The graphene islands terminate with a zigzag edge and moiré-periodic kinks in the regions of the on-top stacked carbon rings. Graphene edges near an Ir(111) monatomic step also show the formation of periodic kinks. STS indicates a significant spatial dependence of the differential conductance dI/dV near graphene edges. We observe a considerably reduced differential conductance at the graphene island edges. We tentatively ascribe these observations to the electronic interaction of graphene with the Ir(111) substrate, which affects the differential conductance differently near graphene edges as compared to the inner part of a graphene island.

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