Site-Dependent Donation/Backdonation Charge Transfer at the CoPc/Ag(111) Interface

Abstract

The organic/metal interface formed upon adsorption of cobalt(II) phthalocyanine (CoPc) molecules on a flat Ag(111) single crystal was investigated using a combination of scanning tunneling microscopy (STM) and photoemission spectroscopy (PES). A flat-lying molecular adsorption with the π conjugated phthalocyanine ligand parallel to the substrate was found to lead to an effective molecule-substrate coupling which governs a template-guided molecular growth. A voltage polarity dependence at the cobalt ion site was emphasized and correlated with the Co 2p core level spectra evolution which sustains an interface-confined reduction effect of the cobalt oxidation state. The formation of interface dipoles was observed via monitoring the changes in the work function (WF) upon deposition. The observations are discussed on the basis of a site-dependent donation/backdonation charge transfer at the molecule-substrate interface.

Heteromolecular metal–organic interfaces: Electronic and structural fingerprints of chemical bonding

“…The model for the line-shape analysis we have used is shown in red and blue color coding for PTCDA and CuPc carbon species, respectively. It is based on own high-resolution and high-statistics XPS measurements and in good agreement with models from literature [3,[64][65][66][67]. The best fits are shown as green lines.…”

Surface chemistry of porphyrins and phthalocyanines

“…Valence band photoemission spectra in the submonolayer range showed two signals at 1.0 and 1.4 eV below E F (see Fig. 39) [249,571], which closely resembled the peak structure predicted for CoPc/Ag(1 1 1) [248], although the absolute peak positions differed from the predictions. The same signal structure was found for CoPc on Ag(1 0 0) [250].…”

“…Instead, the major signal contributions were shifted to lower binding energies and the multiplet structure vanished. The 2p 3/2 and 2p 1/2 components shifted by 1.8 eV and 2.7 eV, which reduced the spinorbit splitting from 15.7 to 14.8 eV [249,571] and thus led to a spectrum characteristic of diamagnetic S=0 cobalt compounds and Co metal. It has been concluded that the Co(II) metal center is reduced by electrons from the Ag substrate [249,571].…”

“…The 2p 3/2 and 2p 1/2 components shifted by 1.8 eV and 2.7 eV, which reduced the spinorbit splitting from 15.7 to 14.8 eV [249,571] and thus led to a spectrum characteristic of diamagnetic S=0 cobalt compounds and Co metal. It has been concluded that the Co(II) metal center is reduced by electrons from the Ag substrate [249,571]. 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).…”

Configuration-specific electronic structure of strongly interacting interfaces: TiOPc on Cu(110)

“…Changing interfacial electronic structure well below the frontier orbitals introduces one final point: Hybridization with the surface occurs not only near E F , but also for lower-energy states. These lower-lying orbitals are often overlooked, but may provide a pathway for charge backdonation to offset the extent of charge transfer accompanying f -LUMO formation [55,56].…”