Rainbow scattering in axial ion-channeling involving very thin crystals: Experimental and theoretical results

Abstract

We have studied the angular scattering distributions produced in axial channeling when incident protons (7 MeV) are well aligned to the axial direction of a thin silicon crystal (1400 Å). Measured angular distributions obtained in the 〈100〉 and 〈110〉 directions using a 2-D position-sensitive detector have been interpreted by comparison with Monte Carlo trajectory calculations for these channels in the momentum approximation. The measured angular distributions show structures at certain off-axis angles which are in good agreement with the calculations. The general shape and structure in the angular contour map for a given channel has been shown to be a consequence of extrema in the 2-D classical deflection functions for the two Cartesian scattering angles in the detection plane. The occurrence of the extrema in a very thin crystal (i.e. a rainbow effect in axial channeling) is a consequence of the channeling geometry when atomic strings surrounding the axial channel interact with the projectile simultaneously.