Energy loss and inelastic diffraction of fast atoms at grazing incidence

The diffraction of fast atoms at grazing incidence on crystal surfaces (GIFAD) was first interpreted only in terms of elastic diffraction from a perfectly periodic rigid surface with atoms fixed at equilibrium position. Recently, a new approach have been proposed, referred here as the quantum binary collision model (QBCM). The QBCM takes into account both the elastic and inelastic momentum transfer via the Lamb-Dicke probability. It suggests that the shape of the inelastic diffraction profiles are log-normal distributions with a variance proportional to the nuclear energy loss deposited on the surface. For keV Neon atoms impinging the LiF surface, the predictions of the QBCM in its analytic version are compared with numerical trajectory simulations. Some of the assumptions such as the planar continuous form, the possibility to neglect the role of lithium atoms and the influence of temperature are investigated. A specific energy loss dependence $\Delta E\propto\theta^7$ is identified in the quasi-elastic regime merging progressively to the classical onset $\Delta E\propto\theta^3$. The ratio of these two predictions highlight the role of quantum effects in the energy loss.Comment: 9 pages 8 figures paper prepared for IISC-2