A first-principles DFT dispersion-corrected C60/Au(111) Raman study

Abstract

We present an extensive density functional theory (DFT) study on the interaction of C60 molecules with Au(111), involving both periodic metal surfaces and clusters. The aim of this work is 2-fold: First, to quantify the adsorption energies per molecule (Eads) of the C60/Au(111) system from periodic calculations using a dispersion-corrected functional (DFT-D3). Secondly, to determine the effect of the metal substrate on the adsorbed C60 molecule via calculated non-resonant Raman vibrational frequencies. Using a commensurate (23×23) R30° phase – as proposed by experimental work as a stable C60/Au(111) monolayer – our DFT-D3 periodic calculations show a slight C60 molecule preference to adsorb on its hexagonal facet, with a calculated adsorption energy value of 2.40 eV. Our DFT-D3 calculations further reveal an energetic gain when the C60 molecule is adsorbed on an HCP surface (2.40 eV) site compared to an FCC one (2.31 eV). Using a variety of finite-size, slab-type Au clusters (e.g.Au24, Au32 and Au50), our DFT-D3 calculated Raman intensity profile shows a strong interaction between the C60 fullerene molecule and the gold substrate. This influences new vibrational modes over a wide range of frequencies, compared to those active modes for the isolated C60 gas-phase single molecule, and an overall shift of frequencies and symmetries. The DFT-D3 calculated Raman spectra of the C60 molecule supported on Au clusters are in good agreement when confronted to those recently obtained experimentally under ultra-high vacuum (UHV) conditions using tip-enhanced Raman spectroscopy (TERS).