Secondary electrons induced by fast ions under channeling conditions. III. Unshadowed electrons in target crystals

Ion-beam shadowing effects have been measured for keV secondary electrons induced by protons, deuterons, and α particles in the energy range of 5.3–8.35 MeV/u, under various channeling conditions in Si, GaAs, and MgO crystals. From a comparison of the electron yields for protons and for the other projectiles of equal velocity, we have determined averaged numbers of the interstitial target electrons that suffer no shadowing effect. This method is useful for investigating the bond-electron distribution in a crystal lattice. Furthermore, the results for deuterons and α particles indicate that the quantum-mechanical diffraction of ions disappears in a series of small-angle scatterings by the aligned atoms, even when the Coulomb-scattering parameter has a nonclassical value (κ=1.1)