Observation of Interference Oscillations in Helium Scattering from Single Surface Defects

Large-angle-diffraction oscillations in the intensity of helium atoms elastically scattered from randomly stepped Pt(111) are reported. A formalism based on the concept of reflection-symmetry interference explains the observed features and the data analysis yields a value of 4.4-4.6 Å for the hard-core repulsive cross section of a single step. The observed oscillations are sensitive to the presence of adsorbates at step sites.