Structural Disordering upon Formation of Molecular Heterointerfaces

The formation of an organic heterointerface is an essential, albeit rather complex, process in the growth of a molecular heterostructure. Sequentially stacking dissimilar molecules occasionally leads to molecular rearrangement, which potentially involves structural perturbation of the first layer. Disorder in the growth process complicates the interface structure and energetic landscape. However, current understanding of this disorder on the molecular scale remains primitive, which hampers the realization of envisioned heterointerface designs. Herein, we used scanning tunneling microscopy to directly observe the disorder upon the formation of sexithiophene (6T, top)/perfluorinated copper phthalocyanine (F16CuPc, bottom) interfaces. Vacuum deposition of 6T onto an epitaxially grown F16CuPc monolayer completely perturbed the molecular arrangement of F16CuPc along the [1–21] direction of the Ag(111) surface. In the disordered structure, the 6T molecules adopted various bent shapes owing to the cis–trans isomerization between the thiophene rings and were randomly mixed with F16CuPc. Comparative experiments demonstrated that (i) multiple C–F···H–C bonds between the F16CuPc and bent 6T molecules stabilized the disordered binary structure and (ii) sparse molecular packing of the F16CuPc monolayer and the conformational variety of 6T led to substantial disorder. This real-space imaging of the disordered structure facilitates the molecular understanding of the structural perturbation and, furthermore, provides design rules for molecular heterointerfaces