Native defects in ultra-high vacuum grown graphene islands on Cu(111)

We present a scanning tunneling microscopy (STM) study of native defects in graphene islands grown by ultra-high vacuum (UHV) decomposition of ethylene on Cu(111). We characterize these defects through a survey of their apparent heights, atomic-resolution imaging, and detailed tunneling spectroscopy. Bright defects that occur only in graphene regions are identified as C site point defects in the graphene lattice and are most likely single C vacancies. Dark defect types are observed in both graphene and Cu regions, and are likely point defects in the Cu surface. We also present data showing the importance of bias and tip termination to the appearance of the defects in STM images and the ability to achieve atomic resolution. Finally, we present tunneling spectroscopy measurements probing the influence of point defects on the local electronic landscape of graphene islands.

Modification of electronic surface states by graphene islands on Cu(111)

We present a study of graphene/substrate interactions on UHV-grown graphene islands with minimal surface contamination using emph{in situ} low-temperature scanning tunneling microscopy (STM). We compare the physical and electronic structure of the sample surface with atomic spatial resolution on graphene islands versus regions of bare Cu(111) substrate. We find that the Rydberg-like series of image potential states is shifted toward lower energy over the graphene islands relative to Cu(111), indicating a decrease in the local work function, and the resonances have a much smaller linewidth, indicating reduced coupling to the bulk. In addition, we show the dispersion of the occupied Cu(111) Shockley surface state is influenced by the graphene layer, and both the band edge and effective mass are shifted relative to bare Cu(111).