Dechanneling by dislocations in ion-implanted Al

Abstract

The first comprehensive ion-backscattering study of the influence of dislocations on the dechanneling of energetic channeled ions has been carried out. High dislocation densities were obtained in the near-surface region of single-crystal Al by implantation of 6.6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ Al/${\mathrm{cm}}^{2}$ or 2.6\ifmmode\times\else\texttimes\fi{}${10}^{16}$ Zn/${\mathrm{cm}}^{2}$. Independent analysis of the disorder introduced by the Al and Zn implantations, as well as a quantitative measure of the total length of dislocation lines per ${\mathrm{cm}}^{2}$, were obtained by transmission-electron microscopy. Dechanneling measurements were made by means of ion backscattering for ${\mathrm{H}}^{+}$ and ${\mathrm{He}}^{+}$ ions ranging in energy from 0.5 to 2.8 MeV, incident along the $〈110〉$ axial and ${111}$ planar channeling directions. For these experimental parameters a systematic dependence of the dechanneling versus depth is demonstrated. These experimental observations are characteristic of that predicted theoretically for dechanneling by dislocations and distinctly different from that observed for randomly displaced atoms. The theoretical analysis for the data reduction is developed to obtain the dechanneling cross section for dislocations from the experimental data for both axial and planar channeling. The results are in agreement with independent theoretical calculations of the dislocation dechanneling cross section by Qu\'er\'e, both quantitatively and in the functional dependences of the dechanneling parameter on energy, ion type, and channeling direction. From these studies the measurement of dislocation density by single alignment channeling is estimated to require ${10}^{9}$-${10}^{10}$ dislocation lines per ${\mathrm{cm}}^{2}$. Although axial channeling has been used in the past for depth profiling measurements of disorder by backscattering, the large dechanneling cross sections and well-defined dechanneling behavior shown here for planar channeling suggest that planar analysis may be more suitable than axial for determining the depth distribution of dislocations by channeling-effect measurements.