Issue 13, 2021

Alkali metal adsorption on metal surfaces: new insights from new tools


The adsorption of sodium on Ru(0001) is studied using 3He spin-echo spectroscopy (HeSE), molecular dynamics simulations (MD) and density functional theory (DFT). In the multi-layer regime, an analysis of helium reflectivity, gives an electron–phonon coupling constant of λ = 0.64 ± 0.06. At sub-monolayer coverage, DFT calculations show that the preferred adsorption site changes from hollow site to top site as the supercell increases and the effective coverage, θ, is reduced from 0.25 to 0.0625 adsorbates per substrate atom. Energy barriers and adsorption geometries taken from DFT are used in molecular dynamics calculations to generate simulated data sets for comparison with measurements. We introduce a new Bayesian method of analysis that compares measurement and model directly, without assuming analytic lineshapes. The value of adsorbate–substrate energy exchange rate (friction) in the MD simulation is the sole variable parameter. Experimental data at a coverage θ = 0.028 compares well with the low-coverage DFT result, giving an effective activation barrier Eeff = 46 ± 4 meV with a friction γ = 0.3 ps−1. Better fits to the data can be achieved by including additional variable parameters, but in all cases, the mechanism of diffusion is predominantly on a Bravais lattice, suggesting a single adsorption site in the unit cell, despite the close packed geometry.

Graphical abstract: Alkali metal adsorption on metal surfaces: new insights from new tools

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Article information

Article type
12 Oct 2020
05 Nov 2020
First published
05 Nov 2020
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2021,23, 7822-7829

Alkali metal adsorption on metal surfaces: new insights from new tools

A. Raghavan, L. Slocombe, A. Spreinat, D. J. Ward, W. Allison, J. Ellis, A. P. Jardine, M. Sacchi and N. Avidor, Phys. Chem. Chem. Phys., 2021, 23, 7822 DOI: 10.1039/D0CP05365A

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