Mapping the electronic structures of a metalloporphyrin molecule on Au(111) by scanning tunneling microscopy and spectroscopy

Abstract

The intramolecular structure of a Co-porphyrin molecule adsorbed on Au͑111͒ is studied using scanning tunneling microscopy and spectroscopy. As the energy is swept from −2 to +2 eV across Fermi level, the shape of the molecular image dramatically evolves from a two-lobed object to a shape with a bright center and, finally, to a four-lobed object. With the help of first-principles calculations, we explain these distinctive features in terms of the integrated molecular orbitals of a saddle conformation and the contribution of a Kondo state. Based on the molecular structure and the orbitals, we explain why the modification in the electronic states of the molecules by the presence of the substrate is relatively modest.

Surface chemistry of porphyrins and phthalocyanines

“…In the valence photoemission spectra of CoTPP/Au(1 1 1) and CoOEP/Au (1 1 1), a new feature between E F and 0.5 eV below E F occurred, which was more intense for CoTPP than for CoOEP and was attributed to the Co-Au interaction [587]. A similar feature was observed by STS on CoTBrPP on Au(1 1 1), in particular at the position of a the protruding pyrrole rings [420].…”

“…The planar molecules were found to form a hexagonal arrangement, whereas the molecules having saddle conformations did not self-assemble (at least under the particular preparation conditions) [419]. In contrast, on Au(1 1 1), CoTBrPP was found to form islands with saddle-shaped molecules [420].…”

“…There are hints that electron donation from the substrate to the Co ion may be accompanied by back donation from the Pc ligand to the substrate [249], as was predicted by theory [199] (see this section above). For CoPcF 16 with its strongly electron accepting substituents, the effects related to electron transfer from the Ag(1 1 1) substrate to the complex were even more pronounced: The difference between the Co 2p 3/2 peak positions for the multilayer and the monolayer was larger (shift of 2 eV towards lower binding energy) and the valence levels were shifted to higher binding energies [ [194,254,259,346,420,470,[573][574][575]580,586,587]. On Au(1 0 0), a new interaction-induced valence signal at 0.48 eV below E F occurred, which was attributed to a downshift and partial occupation of the previously unoccupied 13a 1g MO (mainly the Co 3d z 2) orbital [256]; a more complex valence signal in the same region was found for CoPc on polycrystalline Au [574].…”

“…10.2. Cobalt porphyrins. Studies of adsorbed cobalt(II) porphyrins include CoOEP on Ag(1 1 0) [429], Ag(1 1 1) [426] and Au(1 1 1) [587], CoTPP on Ag(1 1 1) [20,[374][375][376]390,541,589], Au(1 1 1) [400,470,587], polycrystalline Au [391,400], Cu(1 1 0) [386], Cu (1 1 1) [384] and Cu 3 N/Cu(1 1 0) [386], CoTBPP on Ag(1 1 1) [541] and CoTBrPP on Au(1 1 1) [420]. Mixed monolayer phases of CoPc and CoTPP on Au(1 1 1) were also investigated [470].…”

Interfacial coordination interactions studied on cobalt octaethylporphyrin and cobalt tetraphenylporphyrin monolayers on Au(111)

“…Due to the planar structure of the ligands, the metal center can directly interact with the substrate, as was previously shown. 9,10 In particular, there have been various studies of metalloporphyrins on noble metal surfaces with spectroscopic [10][11][12][13] and microscopic methods, 12,[14][15][16][17][18][19][20][21][22] in which the electronic and geometric structure of porphyrin layers have been investigated in detail. Lukasczyk et al studied monolayers of cobalt tetraphenylporphyrin (CoTPP) and cobalt tetrakis(3,5-di-tert-butylphenyl)porphyrin (CoTTBPP) on Ag(111) with XPS and UPS.…”