Determining adsorbate diffusion coefficients on surfaces from helium-3 spin-echo measurements of atomistic dynamics

Surface diffusion is typically described using tracer diffusion coefficients D s , which provides a bridge between atomistic dynamics and macroscopic modeling. Here we introduce a new framework to convert helium-3 spin-echo (HeSE) coherent scattering information into tracer diffusion coefficients D s , systematically distinguishing and treating three different diffusion regimes—Brownian, hopping, and correlated—within a single HeSE analysis framework. HeSE resolves adsorbate motion on both Å length scales and picosecond timescales and yields highly accurate hopping rates and dephasing rates data across a broad range of systems, yet results are seldom reported directly as D s because a standard conversion from the coherent intermediate scattering function has been lacking. By combining analytical models with molecular dynamics simulations where interadsorbate forces are explicitly included, we establish a unified workflow to extract D s , and produce an initial benchmark library of HeSE-derived D s for surface-diffusion studies, providing an experimentally derived tracer diffusion coefficients for a set of adsorbate-substrate systems.