(a) Scanning microscope photograph of the silicon grating surface. Top: Cross-sectional view. Bottom: Expanded view of the ridge. Definition of a period \(d\) and a width \(a\) of the ridge are depicted. (b) The Atomic reflectivities from various ridged surfaces are plotted as a function of normal incident velocity of the atomic beam. The solid line show the reflectivity from the flat surface. Both (a) and (b) are extracted from [Shmizu and Fujita, 2002]