Influence of graphene-substrate interactions on configurations of organic molecules on graphene: pentacene/epitaxial graphene/SiC

Pentacene has been used widely in organic devices, and the interface structure between pentacene and a substrate is known to significantly influence device performances. Here we demonstrate that molecular ordering of pentacene on graphene depends on the interaction between graphene and its underlying SiC substrate. The adsorption of pentacene molecules on zero-layer and single-layer graphene, which were grown on a Sifaced 6H-SiC(0001) wafer, was studied using scanning tunneling microscopy (STM). Pentacene molecules form a quasi-amorphous layer on zero-layer graphene which interacts strongly with the underlying SiC substrate. In contrast, they form a uniformly ordered layer on the single-layer graphene having a weak graphene-SiC interaction. Furthermore, we could change the configuration of pentacene molecules on the singlelayer graphene by using STM tips. The results suggest that the molecular ordering of pentacene on graphene and the pentacene/graphene interface structure can be controlled by a graphene-substrate interaction.