K W Hipps - Scanning Tunneling Microscopy Study of the Structure and Orbital-Mediated Tunneling Spectra of Cobalt(II) Phthalocyanine and Cobalt(II) Tetraphenylporphyrin on Au(111):  Mixed Composition Films

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  Barlow, Dan E., Scudiero, L., Hipps, K. W. Langmuir  2004 20 (11) 4413-4421

  Abstract: Binary thin films of cobalt(II)   phthalocyanine (CoPc) and cobalt(II) tetraphenylporphyrin (CoTPP)   were prepared at submonolayer coverage on Au(111)/mica substrates   by vapor deposition. All sample preparation and analysis were   done under an ultrahigh vacuum. Scanning tunneling microscopy   (STM) constant-current images of CoPc/CoTPP mixtures showed two   close-packed surface structures, with different compositional   percentages and some disorder. CoPc was also observed exclusively   in one-dimensional chains and as single, isolated molecules below   220 K. Occupied and unoccupied orbital energy levels were   identified by STM and tunnel-diode-based orbital-mediated   tunneling spectroscopy. Occupied energy levels were also   confirmed by ultraviolet photoelectron spectroscopy. The   transient oxidation of the Co dz2 orbital is identified in STM   dI/dV(V) curves just negative of the 0 V sample bias for both   molecules. Nearly identical constant-current contours are   observed over the central Co2+ ions of CoTPP and CoPc, indicating   that the attenuation of the dz2 orbital-mediated tunneling   current induced by the structure of TPP relative to Pc is at most   a factor of about 10. The orbital-mediated tunneling spectra of   CoTPP and CoPc are distinctly different and allow these   structurally similar species to be differentially identified.

  Address (URL): http://dx.doi.org/10.1021/la035879l