Structural analysis of PTCDA monolayers on epitaxial graphene with ultra-high vacuum scanning tunneling microscopy and high-resolution X-ray reflectivity

► PTCDA adlayers on graphene are investigated with X-ray and scanning probe techniques. ► PTCDA adlayers are found to be ordered in both lateral and vertical dimensions. ► Results suggest that PTCDA binds to graphene via a π- π* interaction. ► PTCDA may be used for non-covalent functionalization of graphene.