Structural Disordering upon Formation of Molecular Heterointerfaces

Abstract

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 (F 16 CuPc, bottom) interfaces. Vacuum deposition of 6T onto an epitaxially grown F 16 CuPc monolayer completely perturbed the molecular arrangement of F 16 CuPc 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 F 16 CuPc. Comparative experiments demonstrated that (i) multiple C−F•••H−C bonds between the F 16 CuPc and bent 6T molecules stabilized the disordered binary structure and (ii) sparse molecular packing of the F 16 CuPc 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.

Heteromolecular Bilayers on a Weakly Interacting Substrate: Physisorptive Bonding and Molecular Distortions of Copper–Hexadecafluorophthalocyanine

“…In recent years, heteromolecular structures have attracted a significant amount of attention, − especially because of their widespread potential for and use in organic (opto)­electronic devices. In this context, both the electronic and structural properties of the organic layers are highly relevant as they have a strong impact on the charge carrier transport and thus overall device performance. , The energy-level alignment at the organic–organic and organic–inorganic interface, , which is a key issue also for molecular heterostructures, has been the subject of intense research. − For a better understanding of more elaborate thin film architectures, different bicomponent model systems on single-crystal surfaces have been investigated.…”

Photoelectron spectroscopy reveals molecular diffusion through physisorbed template layers on Au(111)

“…The shifts of the CuPc HOMO-levels between thin and thick coverages on PxO pre-covered Au(111) [figures 3(b) and (c)] are slightly smaller than that of CuPc on Au(111) [figure 3(a)] and the fine structure for medium coverages is not apparent. Molecular exchange might be not complete and remaining P2O or P4O molecules on the Au(111) surface will disturb CuPc thin film growth [65,66]. This is corroborated by the sole main difference of the templates layers: by templating Au(111) with P4O [figure 3(c)], CuPc multilayer features appear already for a nominal CuPc thickness of 2 Å, which can be explained by molecular exchange taking place more slowly or only partly.…”

Recent Progress on the Scanning Tunneling Microscopy and Spectroscopy Study of Semiconductor Heterojunctions

“…[ 128 ] Energy levels from DRNC5T:[70]PCBM interfaces show a larger bandgap compared with the interface with thermal annealing treated, which could facilitate the charge transfer between DRNC5T:[70]PCBM and manifest as an improvement in the charge extraction. [ 130–132 ]…”