  The effect produced by surface defects on grazing-incidence fast atom
diffraction (GIFAD) patterns is studied by considering the presence of terraces
in a LiF(001) sample. For helium atoms impinging along the <110> direction of
the LiF surface, we analyze the influence of a monolayer terrace with its edge
oriented parallel or perpendicular to the axial channel. We found that the
presence of an outward transverse step introduces a diffuse background above
the Laue circle, which displays additional peaked structures. For inward
transverse steps, instead, such a background is placed below the Laue circle,
showing a much weaker intensity. On the other hand, parallel steps give rise to
asymmetric angular distributions, which are completely confined to the Laue
circle. Therefore, these theoretical results suggest that GIFAD might be used
to characterize terrace defects.
