Monolayer Structure and Electronic Properties of Fe-Perylenetetracarboxylic-dianhydride (Fe-PTCDA) on Cu(111)

This thesis presents the investigation of PTCDA (3,4,9,10-perylenetetracarboxylicdianhydride)
and Fe-PTCDA complex on Cu(111). Monolayer structure of Fe-PTCDA
was studied by scanning tunneling microscopy (STM); electronic properties of PTCDA
and Fe-PTCDA were measured by scanning tunneling spectroscopy (STS). dI/dV
spectra of PTCDA on Cu(111) revealed the formation of a hybrid state, indicative of a
strong chemical interaction between the adsorbate and substrate. The molecular orbital
involved in the hybridization was LUMO (lowest unoccupied molecular orbital),
confirmed by topographic images. Topographic images of Fe-PTCDA/Cu(111)
revealed a ladder-like structure, which is distinctly different from the herringbone
structure of PTCDA/Cu(111). Two types of molecules were named according to their
orientation in a ladder-like structure, that is, chain- and rung-PTCDA. Topographic
features of chain- and rung-PTCDA resolved at the molecular level are unprecedented.
The images unraveled that both types of molecules had the same occupied molecular state.
However, dI/dV spectra showed that rung-PTCDA have higher density of unoccupied
states compared with chain-PTCDA. This means that the LUMO of rung-PTCDA is
only partially occupied with the electrons donated by Fe. Since chain-PTCDA binds to
4 Fe atoms while rung-PTCDA binds to only 2 Fe atoms, the result showed that the charge
transfer from Fe to PTCDA is coordination number-related.