HeSE has been used to study the diffusion rates and mechanisms of atoms and molecules (adsorbates) at surfaces. A non-exhaustive list of the research themes associated with HeSE diffusion measurements include: 
nuclear quantum effects in the surface diffusion of atomic hydrogen;
benchmarking the adsorbate/surface free energy landscape; 
energy exchange (friction) between adsorbates and the surface; pairwise  and many-body  inter-adsorbate interactions.