High-quality graphene, owing to its extremely high carrier mobility,[1, 2] has emerged as a promising component for nanoscale electrical devices.[3] So far, the fabrication of graphene-based devices has largely relied upon mechanical exfoliation of graphite.[4] However, this method yields only a small number of graphene monolayers, which have to be located in a time-demanding process. An alternative method–epitaxial growth of graphene on silicon carbide [5]–affords high-quality mono-and multi-layers of graphene, but the ultrahigh vacuum required limits its technological applicability. Another route involves chemical vapor deposition (CVD) of hydrocarbons on the surfaces of transition metals, like nickel, with subsequent sheet transfer onto insulating substrates,[6] yielding graphene devices of promising electrical performance. However, the sheets obtained in this manner still lack sufficient structural homogeneity over larger areas. Furthermore, as a general disadvantage of all the aforementioned methods, they do not enable the controlled placement of the graphene, which represents an essential prerequisite for the fabrication of integrated device architectures. For these reasons, significant effort has recently been directed toward solution-based approaches that provide access to larger amounts of graphene monolayers, and furthermore offer the possibility of assembling the sheets at specific, surface-modified areas on a technologically relevant insulating substrate, such as SiO2.[7]

High-quality graphene sheets have been obtained via ultrasonic dispersion of graphite in appropriate organic solvents.[8, 9] However, this has been achieved only with lateral sizes of a few hundreds of nanometers,[8] and at quite low yield.[9] A very promising low-cost, up-scalable synthetic approach comprises the