Lateral adsorption geometry and site-specific electronic structure of a large organic chemisorbate on a metal surface

Abstract

A combined study of scanning tunneling microscopy ͑STM͒ and density functional theory ͑DFT͒ reveals that 3,4,9,10-perylene-tetracarboxylic-dianhydride ͑PTCDA͒ adsorbs on Ag͑111͒ at bridge sites in two nonequivalent orientations, one nearly aligned with the ͓101͔ substrate axis and the other 18°misaligned. Site-specific spectroscopy reveals that molecules in the two configurations exhibit subtle differences in their electronic structure. DFT-based STM simulations trace these back to the influence of distinct local adsorption geometries on the chemical molecule-substrate and molecule-molecule interactions.

Electronic charge rearrangement at metal/organic interfaces induced by weak van der Waals interactions

“…Our study is concluded with a very well-characterized HMOS: PTCDA on Ag(111) [59,60]. The presence of the functional group O=C−O−C=O on both sides of PTCDA enhances the bonding with the metallic surface.…”

Dynamical bistability of single-molecule junctions: A combined experimental and theoretical study of PTCDA on Ag(111)

“…The level below ε F is the former LUMO that gets filled on adsorption and that is clearly observed in scanning tunneling spectroscopy. [26][27][28] The sharp level above ε F that is found in DFT appears in experiments as a broader feature in the gap between the former LUMO and the LUMO + 1, especially for molecules at the edges of monolayer islands. In our minimal model Hamiltonian we can only take one transport level into account.…”

“…The mechanisms of the chemical bonding of PTCDA to Ag(111) includes hybridization of the molecular orbitals with the substrate states, charge transfer between the substrate and the molecule, local bonds of the carboxylic oxygens to silver atoms below, and an extended bond of the molecular π system to the surface. 5,[26][27][28] Assuming that the two metastable positions can be well represented by a (not necessarily symmetric) double-well potential, the transfer of an adsorbate between the two minima may involve a variety of physical processes, such as (i) thermal activation, (ii) quantum tunneling, (iii) a transition through an electronic excited state with no conformational bi-stability, or (iv) vibrational heating. Process (i) is of minor interest in this work, since the experiments are performed at very low temperatures (5-6 K) and the barrier height is larger than 100 meV, which excludes the thermal activation.…”

“…The chemisorption results in the former lowest unoccupied molecular orbital (LUMO) of the isolated molecule being shifted below the Fermi level of the silver surface, so that there is charge transfer from the substrate to the molecule, thus producing a net negative charge on the molecule. 28 In previous experiments we have found that it is possible to form a chemical bond between the carboxylic oxygen atoms and the STM tip, if the latter is approached toward the molecule above one of the carboxylic oxygen atoms: 4,5,8 The oxygen atom, followed by part of the carbon skeleton of the PTCDA molecule, jumps into contact with the tip. The most likely distance for this single switch to happen (without applying a bias voltage) is 6.65Å.…”

“…[25][26][27][28] The PTCDA molecules form long-range ordered commensurate monolayers on the Ag(111) substrate with two flat-lying chemisorbed molecules per unit cell in a herringbone arrangement (see Ref. 25).…”