Transition from axial to planar surface channeling for fast atom diffraction

The diffraction patterns for scattering of fast He atoms from a LiF(0 0 1) surface under a grazing angle of incidence are recorded as function of the azimuthal angle for surface channeling conditions. We observed well defined diffraction patterns which show pronounced changes with the azimuthal rotation of the target surface. Within an azimuth of about 2° the angular distribution turns from a rich pattern to a single peak of zeroth diffraction order only. The data are well reproduced by a semi-classical approach making use of individual pair potentials for the atom surface interaction.