Confinement of the Pt(111) Surface State in Graphene Nanoislands

We present a combined experimental and theoretical study of electron confinement in graphene nanoislands (GNs) grown on a Pt(111) substrate using scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. We observed standing wave patterns in the STM images of GNs, and the bias dependency of the standing wave pattern was reproduced by considering free electrons with an effective mass of <i>m</i>* ≈ (0.27 ± 0.03)<i>m</i>_e. Because the effective mass of Pt is <i>m</i>* = 0.28<i>m</i>_e, our results reveal that the electron confinement is due to the effect of the Pt substrate rather than the massless Dirac electrons of graphene. Our calculated maps of the local density of states (LDOS) for the GNs confirm that the electronic properties of the confinement may be described in terms of electrons with an effective mass. The DFT-calculated charge distribution for graphene on the Pt system also shows a clear hybridization between the p_<i>z</i> orbitals of both the first layer of the Pt substrate and the carbon atoms