J. PHYS. CHEM. LETT.: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.