Ab-initio calculations and STM observations on Tetrapyridyl and Fe(II)-Tetrapyridyl-porphyrin molecules on Ag (111)

Zotti, Linda Angela1; Teobaldi, Gilberto1; Hofer, Werner A.1; Auwarter, Wilhelm2; Weber-Bargioni, Alexander3; Barth, Johannes V.2 1United Kingdom; 2Germany; 3Canada

We modelled the adsorption of TetraPyridyl (TpyP) and Fe(II)- TetraPyridyl (Fe-TPyp) porphyrin molecules on Ag(111). TPyP adsorbs in a flat geometry at a distance of 5.6 Å from the surface. The dihedral angle of the pyridyl rings is found to be 70°. The molecular structure remains largely unaffected by the adsorption. The structure of the molecular adlayer should thus be determined mainly by lateral intermolecular interactions. This conclusion is confirmed by scanning tunnelling microscopy experiments. The spin-polarized d-states of Fe-TPyP are localized near the centre of the gap between the highest occupied (HOMO) and the lowest unoccupied (LUMO) states of a TPyP molecule. We find also that the HOMO-LUMO gap is widened in the presence of Fe. This leads to a shift of 0.3 eV of unoccupied states, which is determined by scanning tunnelling spectroscopy simulations and confirmed by experiments.

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