The Structure of VOPc on Cu(111): Does V═O Point Up, or Down, or Both?

Abstract

The local structure of the nonplanar phthalocyanine, vanadyl phthalocyanine (VOPc), adsorbed on Cu(111) at a coverage of approximately one-half of a saturated molecular layer, has been investigated by a combination of normal-incidence X-ray standing waves (NIXSW), scanned-energy mode photoelectron diffraction (PhD), and density-functional theory (DFT), complemented by scanning tunnelling microscopy (STM). Qualitative assessment of the NIXSW data clearly shows that both “up” and “down” orientations of the molecule (with V=O pointing out of, and into, the surface) must coexist on the surface. O 1s PhD proves to be inconclusive regarding the molecular orientation. DFT calculations, using two different dispersion correction schemes, show good quantitative agreement with the NIXSW structural results for equal co-occupation of the two different molecular orientations and clearly favor the many body dispersion (MBD) method to deal with long-range dispersion forces. The calculated relative adsorption energies of the differently oriented molecules at the lowest coverage show a strong preference for the “up” orientation, but at higher local coverages, this energetic difference decreases, and mixed orientation phases are almost energetically equivalent to pure “up”-oriented phases. DFT-based Tersoff–Hamann simulations of STM topographs for the two orientations cast some light on the extent to which such images provide a reliable guide to molecular orientation.

Elucidating the Geometric Substitution of Petroporphyrins by Spectroscopic Analysis and Atomic Force Microscopy Molecular Imaging

“…This interpretation is supported by previous studies on VOPC on these two adsorption positions. 66−68 We find both species in an approximately 1:1 ratio. The image of VOPC O-down also shows increased repulsive contrast on pyrrolic nitrogens, similar to the petroporphyrins in Figure 4b.…”

A Single-Molecule Chemical Reaction Studied by High-Resolution Atomic Force Microscopy and Scanning Tunneling Microscopy Induced Light Emission

“…VOPc features two distinctively different adsorption conformations − on Ag(111) as well as on bilayer NaCl, which we observed with approximately equal occurrences. Because the aim was to perform STM-LE experiments, we will focus in the following only on VOPc adsorbed on bilayer NaCl, which is necessary for electronic decoupling.…”

“…The two different VOPc species can be distinguished by their appearance in AFM and STM with a CO-functionalized tip, as shown in Figure b,c. From the AFM images, they can be assigned to a conformation with the central oxygen atom pointing away from the surface (O-up) and toward the surface (O-down), respectively. − For the O-up conformation, only the outermost phenylene groups can be resolved by AFM, while in the center, it exhibits an extended repulsive feature stemming from the central oxygen sticking out of the surface plane. In the O-down conformation, the full macrocycle can be resolved by AFM.…”

Observation of Yu–Shiba–Rusinov States and Inelastic Tunneling Spectroscopy for Intramolecule Magnetic Exchange Interaction Energy of Terbium Phthalocyanine (TbPc) Species Adsorbed on Superconductor NbSe2

“…When the TiO 64 and Sn 66 , 68 , 69 are pointing down, the bonding to the surface is less stable than in the case of pointing up. The former is like standing with a single leg on the surface, tilted or dragged by the STM tip.…”