Structure and Molecule–Substrate Interaction in a Co-octaethyl Porphyrin Monolayer on the Ag(110) Surface

Abstract

We present a combined experimental and theoretical study of the ultrathin film of Co-octaethylporphyrin (Co-OEP) molecules deposited on the Ag(110) surface. The morphological and electronic properties of this heterogeneous metallorganic interface were studied by means of scanning tunneling microscopy (STM), near-edge X-ray adsorption fine structure (NEXAFS) spectroscopy, ultraviolet photoemission spectroscopy (UPS), and density functional theory calculations (DFT). The long-range self-ordered single layer of Co-OEP was obtained by thermal desorption of the molecular multilayer. The single-layer molecules were arranged in a noncommensurate rectangular lattice aligned with the substrate high-symmetry directions. The combination of experimental techniques and numerical simulations indicated that in this configuration each molecular macrocycle is tilted with respect to the metal surface of about 15°. The strong molecular interaction with the substrate leads to the electron transfer from the metal substrate to the molecule. The direct interaction with the substrate involves mostly the Co metal center, which modifies the valence state with respect to the free Co-OEP molecules due to the hybridization between Co states and Ag bands.

Surface chemistry of porphyrins and phthalocyanines

“…24a), which was aligned with its short side along the [11̄0] high-symmetry direction of the substrate (and thus with the long side along [001]) [429]. Comparison with the near-hexagonal structures found on Ag(1 1 1) illustrates the influence of the substrate on the adsorbate superstructure.…”

“…By this mechanism, electron density is donated from the Ag surface to the Co ion and partially returned to the substrate via the nitrogen atoms [426]. Similar strong Co-Ag interaction, mediated by the Co d z 2 orbital, and partial reduction of the Co ion occurred in CoOEP/Ag (1 1 0), for which an intense interaction-induced state at 0.65 eV below E F was observed [429].…”

“…STM investigation of a thin multilayer ($ 3 ML) of CoOEP on Ag (1 1 0) revealed the presence of various locally ordered domains with different intermolecular distances and molecular orientation. The mobility of the molecules in the thin multilayer was sufficently low for STM imaging at room temperature [429].…”

“…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].…”

Organic Molecules on Noble Metal Surfaces: The Role of the Interface

“…New interesting results have been achieved recently, as for example a Kondo effect related to the spin of the central atom in Co and Fe phtalocyanines on Au(111), the induced magnetic order of Mn porphyrins on Co films as well as magnetic coupling effects (Wende et al 2007cited in Fanetti et al 2011. Recently in the CoEOP deposited onto Ag(110) (Fanetti et al 2011), a charge transfer to the LUMO orbital has been found. DFT calculations indicate that the molecular interaction with the substrate leads to the electron transfer from the Ag substrate to the molecule.…”