Bragg reflection of low-energy positrons from the surface of graphite

Abstract
We observe Bragg peaks in the elastic backscattering probability of monoenergetic positrons from the [0001] surface of highly oriented pyrolytic graphite. The position of most of the peaks can be explained by a plane spacing d, slightly contracted from the bulk value and a +1.4±0.5-eV positron work function for this surface. An unexpected peak at kdπ=3.5, where k is the positron momentum, could be due to multiple-scattering effects.