Electronic Decoupling of Organic Layers by a Self-Assembled Supramolecular Network on Au(111)

A cyanuric acid and melamine (CA·M) supramolecular network, prepared via the drop-casting method under ambient conditions, can be utilized as a spacer layer to decouple electronic interactions between upper organics and the metal substrate. Typical semiconducting organics 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) and C₆₀ are deposited on the CA·M network under ultrahigh vacuum conditions, forming an organics/CA·M/metal heterosystem. Both geometric and electronic structures of the upper organics are characterized by using scanning tunneling microscopy/spectroscopy (STM/STS). On the CA·M network, PTCDA molecules form a well-ordered herringbone structure in submonolayer patterns, whereas C₆₀ molecules aggregate into multilayered islands. STS spectra reveal that the energy gap between the highest occupied and the lowest unoccupied molecular orbitals (HOMO - LUMO) is 3.6 eV for PTCDA and 3.8 eV for the first layer of C₆₀ on CA·M. The remarkable bandgap broadening compared with the metal-organic contact indicates successful electronic decoupling of the upper molecules from the metal surface due to the CA·M network.