  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).
