Ion channeling in ultra thin crystals

Abstract

Freestanding 55 nm thick [001] silicon membranes were fabricated over several square millimeters. The axial and planar transmission ion-channeling patterns (Rainbows) were recorded by YAG scintillator screen using focused and highly collimated MeV protons from CIBA accelerator. The patterns are confirmed with FLUX & Rainbow simulations. Separate axial and planar channeling effects were discovered from narrow {111} planes for the first time and the patterns resolved the offset in atomic rows forming the narrow {111} planes as well. The existence of the super-focusing effect (<8 pm spot sized MeV protons) was proved, which was predicted only by simulations. Instead of a ring-like ?doughnut? channeling distribution, geometric shapes such as squares and hexagons were observed and also found that they rae the manifestations of the rainbow effect which is proved using the theory of crystal rainbows. Our study opened a route to refine the inter-atomic potentials precisely in future.