PHONONS LOCALIZED AT STEP EDGES - A ROUTE TO UNDERSTANDING FORCES AT EXTENDED SURFACE-DEFECTS

Inelastic helium atom scattering has been used to measure the phonons on a stepped metallic crystalline surface, Ni(977). When the scatterin g plane is oriented parallel to the step edges and perpendicular to th e terraces, two branches of step-induced phonons are observed. These b ranches are identified as transversely polarized, step-localized modes that propagate along the step edge. Analysis reveals significant anis otropy in the force field near the step edge, with all forces near the step edge being substantially smaller than in the bulk. Such measurem ents provide valuable information on metallic bonding and interface st ability near extended surface defects.