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

摘要

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 niicroscopy (STM) constant-current images of CoPc/CoTPP nixtures 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 d_z~2 orbital is identified in STM dI/dV(V) curves just negative of the O V sample bias for both molecules.Nearly identical constant-current contours are observed over the centrál Co~2+ ions of CoTPP and CoPc,indicating that the attenuation of the d_z~2 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.