Template-directed assembly of pentacene molecules on epitaxial graphene on Ru(0001)

The template-directed assembly of planar pentacene molecules on epitaxial graphene grown on Ru(0001) (G/Ru) has been investigated by means of low-temperature scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. STM experiments find that pentacene adopts a highly selective and dispersed growth mode in the initial stage. By using DFT calculations including van der Waals interactions, we find that the configuration with pentacene adsorbed on face-centered cubic (fcc) regions of G/Ru is the most stable one, which accounts for the selective adsorption at low coverage. Moreover, at high coverage, we have successfully controlled the molecular assembly from amorphous, local ordering, to long-range order by optimizing the deposition rate and substrate temperature. Graphical abstract: [Figure not available: see fulltext.]