Amorphous phase formation in Mn-implanted Al films and single crystals.

Abstract

The amorphization of Al thin films and single crystals by Mn implantation at liquid-nitrogen temperature was studied by x-ray diffraction, Rutherford-backscattering and channeling experiments. Structural changes, the lattice site occupation of the implanted Mn atoms, static displacements of the lattice atoms, and the accumulation of strain could be directly observed as a function of manganese concentration. It was found that at low Mn concentrations (5 at. %) the impurities occupy mainly substitutional lattice sites (${f}_{s}$\ensuremath{\simeq}90%). In this concentration range the atomic-size mismatch leads to static displacements of the host lattice atoms. Measurements further suggest that the regions in the immediate vicinity of the Mn impurity atoms are severely distorted. When the local Mn concentration and thus the local distortions exceed a threshold value, the matrix becomes unstable and amorphous clusters are formed throughout the sample. The critical local Mn concentration for amorphization was found to be ${c}_{c}$=8.5 at. % and the minimum volume of the amorphous clusters ${v}_{c}$=2\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}21}$ ${\mathrm{cm}}^{3}$ which is the volume of a sphere with a radius of 3 interatomic distances.