The dynamics of benzene on Cu(111): a combined helium spin echo and dispersion-corrected DFT study into the diffusion of physisorbed aromatics on metal surfaces

Abstract

We use helium spin-echo spectroscopy (HeSE) to investigate the dynamics of the diffusion of benzene adsorbed on Cu(111). The results of these measurements show that benzene moves on the surface through an activated jump-diffusion process between the adsorption sites on a Bravais lattice. Density Functional Theory (DFT) calculations with van der Waals (vdW) corrections help us understand that the molecule diffuses by jumping through non-degenerate hollow sites. The results of the calculations shed light on the nature of the binding interaction between this prototypical aromatic molecule and the metallic surface. The highly accurate HeSE experimental data provide a quantitatively stringent benchmark for the vdW correction schemes applied to the DFT calculations and we compare the performances of several dispersion interaction schemes.

Material properties particularly suited to be measured with helium scattering: selected examples from 2D materials, van der Waals heterostructures, glassy materials, catalytic substrates, topological insulators and superconducting radio frequency materials

“…For example, comparing such potentials for weakly physisorbed species has offered a way of examining the quality of different dispersion correction schemes for DFT approaches. 120 Interaction potentials between adsorbed species also have a dramatic influence on surface processes, causing correlations in motion, and ultimately driving adsorption structures, self-organisation and islanding. HeSE enables these interactions to be studied directly, and measurements have revealed dramatic deviations from widely accepted theory.…”

Transfer matrix theory of surface spin echo experiments with molecules

“…Since Φ E R R (x) ∈ C 1 (x) for a specific value of R and given Eqn. (26), we get the defining equations for the continuity of the wavefunction as…”

“…HeSE experiments [1,2] have been used to study surface morphology [3], molecular and atomic surface diffusion [4][5][6][7][8][9][10], inter-adsorbate forces [8,11], phonon dispersions [12,13], phason dispersions [14], structures and phase transitions of ionic liquids [15] and friction between adsorbates and surfaces [16,17]. HeSE experiments have improved our understanding of potential energy surfaces [18][19][20] and surface-adsorbate interactions [21][22][23][24] and are frequently combined with microscopic calculations to both test theory and gain insight into surface-adsorbate interactions [25,26]. However, the interactions between 3 He and surfaces or their adsorbates are typically isotropic and relatively weak.…”

Transfer-matrix theory of surface spin-echo experiments with molecules

“…Surface-sensitive HeSE experiments [31][32][33] have been used to study surface morphology [36], molecular and atomic surface diffusion [32,33,[37][38][39][40][41], inter-adsorbate forces [38,42], phonon dispersions [32,33,43], phason dispersions [44], structures and phase transitions of ionic liquids [45] and friction between adsorbates and surfaces [46][47][48]. HeSE experiments have provided information about potential energy surfaces [32,33,49] and surface-adsorbate interactions [32,33,50] and are frequently combined with microscopic calculations to both test theory and gain insight into surface-adsorbate interactions [39,51,52].…”