Determination of surface-defect concentration and distribution with He diffraction

A pronounced triangular background, observed near the specular beam with He diffraction from Ni(100)-c(2×2)O, is explained by hard-wall calculations as originating from a random distribution of 15% empty oxygen sites in good agreement with Auger calibration. Lateral adatom relaxations of 0.25 A away from the empty sites fit both the background shape and intensity. This is the first application of He scattering for defect characterization at high coverages. © 1986 The American Physical Society.