Kelvin Probe Microscopy of Single- and Multi-layer Graphene on SiO$_{2}$.*

Kelvin probe microscopy (KPM) was carried out on mechanically exfoliated graphene samples on SiO$_{2}$ in conjunction with standard atomic force microscopy. Potential differences between the SiO$_{2}$ substrate and graphene flakes were large relative to the average fluctuations over the surface of the graphene. KPM shows a consistent surface potential variation between monolayer, bilayer, and multi-layer graphene, and over folded pleats occasionally found in graphene. The source of these surface potential differences will be discussed.