Self-diffusion at a melting surface observed by He scattering

Self-diffusion at surfaces can be studied with quasielastic scattering of low-energy He atoms. This is demonstrated for the Pb(110) surface close to the melting point, ${\mathrm{T}}_{\mathrm{m}}^{\mathrm{Pb}=600.7\mathrm{}}$ K. From the width of the quasielastic energy distribution of scattered He atoms it is inferred that at T≥450 K the surface atoms are anomalously mobile. At T≥550 K, surface mobilities are found to exceed the bulk liquid value. These results complement recent ion-scattering measurements on surface disorder of Pb(110).