| Scanning tunneling microscopy (STM) images of cobalt(II) phthalocyanine (CoPc), copper(II) phthalocyanine (CuPc), iron(II) phthalocyanine (FePc), and nickel(II) phthalocyanine (NiPc) adsorbed on the Au(111) surface are reported. These species provide images showing sub-molecular structure. A particularly exciting aspect of this work is the strong influence of the metal ion valence configuration on the observed tunneling images. Unlike CuPc and NiPc, wherein the central metal appears as a hole in the molecular image, the cobalt ion in CoPc and iron ion in FePc are the highest points (about 0.25 nm) in the molecular images. These data are interpreted as indicating that the Co(II) d{dollar}sp7{dollar} and Fe(II) d{dollar}sp6{dollar} systems have significant d-orbital character near the Fermi energy while the Cu(II) d{dollar}sp9{dollar} and Ni(II) d{dollar}sp8{dollar} systems do not. This interpretation is consistent with theoretical calculations that predict a large contribution of cobalt and iron d-orbitals near the Fermi energy. 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.; A commercial Digital Instruments NanoScope III controller was used with a McAllister Technical UHV STM. Modifications of the preamp, cabling, and coarse approach mechanism were required to achieve satisfactory operation, and these changes are described. Also included are detailed instructions for tip fabrication and final (UHV) electron bombardment cleaning. |
