Structure and vibrational properties of the PTCDA/Ag(1 1 1) interface: bilayer versus monolayer

Abstract

The structural and vibrational properties of metal-organic interfaces have been examined by means of infrared (IR) absorption spectroscopy and density functional theory (DFT) with an approach accounting for long-range dispersive interactions. We focus on a comparative study of the PTCDA monolayer and bilayer on Ag(1 1 1). The equilibrium geometry at the molecule-metal interface and the IR spectrum of the chemisorbed monolayer of PTCDA on Ag(1 1 1) are well described by the computations. In the bilayer structure, the presence of a physisorbed adlayer on top of PTCDA/Ag(1 1 1) presents a challenge for DFT. As previously described for other systems, the polarization of the substrate is not captured correctly and results in too low energies of frontier molecular orbitals. This results in an apparent contribution from the vibrations of second-layer PTCDA to the IR spectrum due to interfacial dynamical charge transfer processes. After removing these peaks with artificially strong intensity, calculated and experimental data show good agreement and the IR spectrum can be described as the sum of the spectra of the PTCDA/Ag(1 1 1) contact layer and a physisorbed PTCDA monolayer on top.

Reaction Pathway toward Seven-Atom-Wide Armchair Graphene Nanoribbon Formation and Identification of Intermediate Species on Au(111)

“…37−39 Typically, for physisorbed or only weakly interacting adsorbates on a metal surface the frequency shifts between multilayer and the first layer are only marginal (Δν < 10 cm −1 ), 39−41 while for chemisorbed systems the frequency shifts are more severe (Δν ≈ 10−100 cm −1 ). 38,39,42 Apparently, no strong interaction exists between the DBBA molecule and the Au(111) surface, in accordance with NEXAFS results 15 which excluded chemisorption for the present system.…”

Doping-Induced Electron Transfer at Organic/Oxide Interfaces: Direct Evidence from Infrared Spectroscopy

“…IRRAS allows detecting charge transfer across the interface by measuring adsorption-induced changes of molecular vibrational frequencies. For metal substrates, IRRAS has already been applied successfully to evidence interfacial charge transfer by detecting frequency shifts of vibrations in molecular adsorbates. − For PTCDA, another common, planar aromatic compound, adsorbed on Ag(111), the changes in frequency were found to amount to 10–30 cm –1 . However, similar studies for molecular adsorbates on wide band gap inorganic semiconductors have not yet been reported.…”

Covalent Attachment and Characterization of Perylene Monolayers on Si(111) and TiO2 for Electron-Selective Carrier Transport

“…As indicated by guide lines with a 10 cm –1 shift, peaks at 1647, 1657, 1698, 1724, and 1759 cm –1 for surface species 2a demonstrate good agreement to spectral features in the molecular species and of molecule 8 in particular. A comparable spectral shift exists for noncovalently bound molecular crystalline adsorbates on metal and silicon surfaces. ,, We ascribe the shift in chemical features to clustering of the adsorbed perylenes in their reaction with an aniline-terminated surface. Separately, each spectrum contains features at 1591–1595 and 1575–1579 cm –1 that indicate perylene C–C ring vibrations.…”

“…A comparable spectral shift exists for noncovalently bound molecular crystalline adsorbates on metal and silicon surfaces. 34,35,54 We ascribe the shift in chemical Activation of Terminal Perylene Cyclic Anhydrides and Conversion to Esters. Quantifying perylene surface coverage of 2a and 2b as well as determining a respective conversion efficiency from 1a and 1b presents challenges.…”