The interaction of channeled ions with foreign atoms in crystals

Quantitative interpretation of channeling experiments for the location of foreign atoms in a crystal depends on the interaction of channeled ions with substitutional and interstitial atoms respectively. The interaction with substitutional atoms has been investigated experimentally, using a solid solution of∼2 at. per cent Au in a Cu single crystal. In an angular scan across the <110> axis, the angular dependence of the back-scattered yield from the Au atoms is found to be identical to that from the Cu atoms. For interstitial atoms the interaction yield is known to depend on the flux peaking for a channeled beam. This has been studied by computer simulations of 4He channeling in the <110> direction in Cu. The dependence of flux peaking on depth in the crystal and the incident ion energy has been investigated, and the variation with angle of incidence of the flux at different interstitial sites calculated. It is found that the normalized width and position of any peak (or dip) in an angular scan are more useful than the peak height in determining the location of interstitial atoms.