Geometric and Electronic Behavior of C60 on PTCDA Hydrogen Bonded Network

Self-assembled supramolecular networks are promising spacer layer for electronic decoupling from the metal substrate. However, the mechanism behind of how the intrinsic electronic structure of spacer layers affects the adsorbate is still unclear. Here a hydrogen bonded network composed of n-type semiconducting molecules 3,4,9,10-perylene-tetracarboxylic-dianhydride(PTCDA) is prepared under ultra-high vacuum to serve as a spacer layer for functional organics C60 on Au(111). The geometric and electronic information of C60 was investigated by scanning tunneling microscopy and scanning tunneling spectroscopy(STM/STS) at 5 K. Effective decoupling from the metal surface yields an energy gap of 3.67 eV for C602nd, merely considering the HOMO-LUMO peak separation. The broadening of resonance peaks in STS measurements however indicates unneglected interlayer interactions in this hetero-organic system. Moreover, we scrutinize the nucleation sites of C60 on PTCDA layer and attribute this to the decreased diffusion capability on a less dense molecular arrangement possessing inhomogeneous spatial distribution of unoccupied molecular orbitals.