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

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