How Atomic Steps Modify Diffusion and Inter-adsorbate Forces: Empirical Evidence From Hopping Dynamics in Na/Cu(115)

TL;DR

This study uses helium spin echo spectroscopy and simulations to reveal how atomic steps on Cu(115) surfaces influence Na atom diffusion, interactions, and collective motion at atomic scales.

Contribution

It provides empirical evidence on how atomic steps modify diffusion and inter-adsorbate forces, highlighting anisotropic hopping and screening effects.

Findings

Na atoms perform anisotropic 1D hopping parallel to steps

Atomic steps screen lateral interactions between Na atoms

Collective motion shows spatial and temporal anisotropy

Abstract

We followed the collective atomic-scale motion of Na atoms on a vicinal Cu(115) surface within a time scale of pico to nano-seconds using helium spin echo spectroscopy. The well defined stepped structure of Cu(115) allows us to study the effect that atomic steps have on the adsorption properties, the rate for motion parallel and perpendicular to the step edge and the interaction between the Na atoms. With the support of a molecular dynamics simulation we show that the Na atoms perform strongly anisotropic one dimensional hopping motion parallel to the step edges. Furthermore, we observe that the spatial and temporal correlations between the Na atoms which lead to collective motion are also anisotropic, suggesting the steps efficiently screen the lateral interaction between Na atoms residing on different terraces.