Surface characterization of sulfur and alkanethiol self-assembled monolayers onAu

We demonstrate that it is possible to mechanically exfoliate graphene under ultrahigh vacuum conditions on the atomically well defined surface of single crystalline silicon. The flakes are several hundred nanometers in lateral size and their optical contrast is very faint, in agreement with calculated data. Single-layer graphene is investigated by Raman mapping. The graphene and 2D peaks are shifted and narrowed compared to undoped graphene. With spatially resolved Kelvin probe measurements we show that this is due to p-type doping with hole densities of nh ' 6× 1012 cm−2. The in vacuo preparation technique presented here should open up new possibilities to influence the properties of graphene by introducing adsorbates in a controlled way. (Some figures may appear in colour only in the online journal)