Fast atom diffraction during grazing scattering from a MgO(001) surface

Fast neutral atoms and molecules with energies from 0.4 up to 3 keV are scattered under a grazing angle of incidence from a clean and flat MgO(001) surface. For “axial surface channeling” conditions, we observe defined diffraction patterns in the angular intensity distributions for scattered ³He and ⁴He atoms as well as H₂ molecules. The diffraction patterns are analyzed in terms of semiclassical trajectory calculations making use of projectile surface interaction potentials derived from density functional theory and from pair potentials calculated from Hartree–Fock wave functions. From comparison of measured and calculated diffraction patterns we deduced the rumpling of the topmost surface layer of MgO(001), i.e. an inward shift of Mg²⁺ ions with respect to O^2? ions, of (0.03±0.03) Å.