RANDOM SPECTRUM FOR THE CHANNELING-BACKSCATTERING TECHNIQUE - A ROTATING AXIAL-DIP STUDY

The (100) axial channeling dip for a Si single crystal, obtained by averaging over azimuthal angles, is studied experimentally and by Monte Carlo simulation for tilt angles theta up to 16-degrees using a 1.5 MeV energy He-4+ ion beam. Both in the experiment and the simulation, the dip shape is found to be in a quantitative agreement with the rule of angular compensation; the influence of the (100) axis extends to theta almost-equal-to 6-degrees. Surprisingly strong fine structure in the yield, with a number of distinct secondary dips, is observed for theta > 6-degrees. It is shown that this structure is related to some high-index crystallographic planes being nearly tangent to the azimuthal scans at certain tilts. Good agreement between the experiment and simulation is obtained at all tilt angles investigated. Consequences for the random yield determination in channeling studies are discussed.