It was pointed out that self-diffusion at surfaces could be studied via the quasi-elastic scattering of low-energy He atoms. The method was applied to (110) Pb surfaces at temperatures close to the melting point of 600.7K. From the width of the quasi-elastic energy distribution of scattered He atoms, it was deduced that - at temperatures greater than 450K - the surface atoms were anomalously mobile. At temperatures greater than 550K, the surface mobilities were found to exceed the bulk liquid value.

J.W.M.Frenken, J.P.Toennies, C.Wöll: Physical Review Letters, 1988, 60[17], 1727-30