Fast-Atom Diraction at Surfaces

Fast helium atoms diracted at alkali-halide surfaces under grazing angles of incidence exhibit intriguing diraction patterns. The persistence of quantum coherence is remarkable, considering high surface temperatures and high (keV) kinetic energies of the incident atoms. Dissipative and decohering eects such as the momentum transfer between the incident helium atoms and the surface inuence the diraction patterns and control the width of the diraction peaks, but they are weak enough to preserve the visibility of the diration patterns. We perform an ab initio simulation of the quantum diraction of fast helium beams at a LiF (100) surface in the h110i direction. Our results agree well with recent experimental diraction data.