Self-assembly of ClAlPc molecules on moiré-patterned graphene grown on Pt(111)

Abstract

Phthalocyanines are promising molecules for the development of organic electronic devices, for instance, molecular heterojunctions in organic solar cells or organic field-effect transistors. For an optimum performance of these devices, the molecular ordering on the substrate and the molecular electronic level alignment have been shown as crucial factors. In this work, the self-assembled structure and the electronic structure of chloroaluminum phthalocyanines (ClAlPc) on graphene grown on Pt(111) surfaces have been studied by scanning tunneling microscopy (STM) under ultrahigh vacuum (UHV) and low-temperature conditions. Graphene grown on Pt(111) exhibits multiple moiré patterns with different periodicities, offering a benchmark to investigate the influence of the graphene and the moiré patterns in the ClAlPc ordering. This surface allows to extend previous works performed on graphite and graphene on Cu(100), where no moiré patterns are found. Well-ordered molecular islands exhibiting rotational domains have been observed in the submonolayer regime. The orientation of individual ClAlPc molecules within the structure unit cell has been characterized pointing out to a Cl-Up configuration adopted by the molecules. Our measurements show a correlation between the molecular lattice orientation and the graphene directions, whereas no influence of the underlying moiré patterns has been found. Finally, the ClAlPc electronic structure has been characterized indicating a weak graphene-molecule interaction.