Locally altering the electronic properties of graphene by nanoscopically doping it with Rhodamine 6G

We show that Rhodamine 6G (R6G), patterned by dip-pen nanolithography on graphene, can be used to locally n-dope it in a controlled fashion. In addition, we study the transport and assembly properties of R6G on graphene and show that in general the π-π stacking between the aromatic components of R6G and the underlying graphene drives the assembly of these molecules onto the underlying substrate. However, two distinct transport and assembly behaviors, dependent upon the presence or absence of R6G dimers, have been identified. In particular, at high concentrations of R6G on the tip, dimers are transferred to the substrate and form contiguous and stable lines, while at low concentrations, the R6G is transferred as monomers and forms patchy, unstable, and relatively ill-defined features. Finally, Kelvin probe force microscopy experiments show that the local electrostatic potential of the graphene changes as function of modification with R6G; this behavior is consistent with local molecular doping, highlighting a path for controlling the electronic properties of graphene with nanoscale resolution.