Graphene Template for Epitaxial Growth of Pentacene and C$_{60}$ Thin Film

The study and reliable control of molecular packing structures at the graphene-molecule interface are of great importance for various applications. We utilize suspended graphene as an assembly template to investigate thin-film epitaxial growth of various organic molecules. Thin-film packing structures of pentacene and C$_{60}$ on graphene are investigated using transmission electron microscopy. For pentacene thin-film, we observe an unusual polymorph growth on graphene, which shows significant strain along the c-axis of pentacene crystals. Moreover, the strained film exhibits a specific molecular orientation and a strong azimuthal correlation with underlying graphene lattice. For C$_{60}$ crystals, we observe large grain sizes and somewhat strong azimuthal correlation with respect to underlying graphene lattice direction. Utilizing \textit{ab initio} electronic structure calculations with van der Waals interactions, we understand the observed molecular growth behavior mainly with graphene-molecule interaction.