Diffraction and Selective Adsorption of Atoms at Crystal Surfaces

Abstract

IN two interesting papers on the reflection and diffraction of helium from crystal surfaces, Frisch and Stern¹ have shown that reflected and diffracted beams are sometimes unexpectedly weak. They examined the conditions under which this anomalous behaviour occurred, and found that it depended on the existence of a relation between the components of momentum of the impinging atoms. The results are reproduced in Fig. 1. Each small circle gives the relation between the component of momentum parallel to one of the axes in the surface lattice (py) and that perpendicular to the surface (pz) for an incident beam which gave weak reflection. Each dot gives the components of momentum of a weak diffracted beam (py and pz). This figure shows clearly that the relation between py and pz for weak reflection is the same as that of py and pz for weak diffraction, and that the sets of points lie on two distinct curves.