Anomalous thermal behavior of the Fe(100) surface observed by grazing ion-surface scattering

Abstract
We show that scattering of 25-keV He+ ions under the condition of planar surface channeling offers a sensitive technique to study the thermal behavior of metal surfaces. The angular distributions of scattered projectiles directly depend on thermal displacements of surface layer atoms and reveal characteristic features caused by scattering at surface steps. Based on computer simulations we deduce an anomalous increase of the mean-square displacement normal to the surface for temperatures above about 750 K. An increase in the density of surface steps can be excluded.