Stochastic theory of lineshape broadening in quasielastic He atom scattering with interacting adsorbates

TL;DR

This paper develops a stochastic model using Langevin dynamics to describe the broadening of quasielastic He atom scattering peaks caused by interacting adsorbates on surfaces, matching experimental data.

Contribution

It introduces a stochastic approach with dual noise sources to model adsorbate interactions and surface diffusion, providing a new theoretical framework for interpreting scattering data.

Findings

Model accurately reproduces experimental peak broadening.

Effective at coverages up to 20%.

Matches data at 200 and 300 K.

Abstract

The activated surface diffusion of interacting adsorbates is described in terms of the so-called interacting single adsorbate approximation, which is applied to the diffusion of Na atoms on Cu(001) for coverages up to 20% in quasielastic He atom scattering experiments. This approximation essentially consists of solving the standard Langevin equation with two noise sources and frictions: a Gaussian white noise accounting for the friction with the substrate, and a white shot noise characterized by a collisional friction simulating the adsorbate-adsorbate collisions. The broadenings undergone by the quasielastic peak are found to be in very good agreement with the experimental data reported at two surface temperatures 200 and 300 K.