Channeling flux in single crystals with interstitial atoms: Impurity concentration dependence

The dependence upon interstitial impurity concentration of the flux of channeled particles has been determined both experimentally and by computer simulations. Experiments were carried out on $\mathrm{Ti}{\mathrm{O}}_x$, with $x$ ranging from 0.11 to 0.39, and computer simulations on $\mathrm{Si}{\mathrm{B}}_x$, with $x$ ranging from 0.1 to 0.5. The similarity between the two systems was checked by computer, with particular reference to the relative strength of the interstitial and lattice-atom arrays. Both experiments and calculations show that the interstitial string is much more effective than the plane; in fact, channeling effects due to the former are clearly displayed for $x=0.2\mathrm{}$, while the latter does not produce any channeling effect up to $x=0.5\mathrm{}$. The computer calculations show that these results can be understood in terms of the relative effect of the host-lattice and interstitial-array potentials. Both experiments and calculations show that at an intermediate incidence angle between axial and planar orientations the beam can distinguish between stronger and weaker strings and penetrates with preference near the latter ones, giving rise to a much higher yield at the interstitial site.