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Scanning tunneling microscopy (STM) images of iron(II) phthalocyanine (FePc) and nickel(II) phthalocyanine (NiPc) adsorbed on the Au(111) surface are reported. Both species provide images showing submolecular structure. A particularly exciting aspect of this work is the strong influence of the metal ion valence configuration on the observed tunneling images. Unlike NiPc, wherein the central metal appears as a hole in the molecular image, the iron ion in FePc is the highest point (about 0.25 nm) in the molecular image. These data are interpreted as indicating that the Fe(II) d 6 system has significant d orbital character near the Fermi energy while the Ni(II) d 8 system does not. This interpretation is consistent with theoretical calculations that predict a large contribution of iron d orbitals near the Fermi energy. The results reported here are also fully consistent with our previous report of CoPc and CuPc d orbital dependent images. An intriguing aspect of this work is that it may be possible to chemically identify different metal complexes simply by their appearance. Metal−organic complex systems of this type may also be viewed as single molecular electronic structures with different parts of the same molecule behaving as insulator, conductor, or semiconductor.
Lu et al. (Tue,) studied this question.