Inter-adsorbate forces and coherent scattering in helium spin-echo experiments

TL;DR

This paper presents a method to separate inter-adsorbate forces from substrate effects in helium spin-echo experiments, enabling clearer analysis of adsorbate interactions during surface diffusion.

Contribution

It introduces a novel approach to disentangle adsorbate-adsorbate interactions from substrate effects in helium scattering data, especially for systems with strong inter-adsorbate forces.

Findings

Method effectively isolates inter-adsorbate interactions

Application to sodium on copper (111) demonstrates the approach

Enhances understanding of adsorbate dynamics and interactions

Abstract

In studies of dynamical systems, helium atoms scatter coherently from an ensemble of adsorbates as they diffuse on the surface. The results give information on the co-operative behaviour of interacting adsorbates and thus include the effects of both adsorbate-substrate and adsorbate-adsorbate interactions. Here, we discuss a method to disentangle the effects of interactions between adsorbates from those with the substrate. The result gives an approximation to observations that would be obtained if the scattering was incoherent. Information from the experiment can therefore be used to distinguish more clearly between long-range inter-adsorbate forces and the short range effects arising from the local lattice potential and associated thermal excitations. The method is discussed in the context of a system with strong inter-adsorbate interactions, sodium atoms diffusing on a copper (111) surface.