Amorphization process in manganese-implanted aluminium thin films and single crystals: Effects of strains and target temperature

Abstract

The amorphization of aluminium thin films and single crystals by implantation at liquid nitrogen temperature (LNT) and room temperature (RT) was studied by X-ray diffraction, Rutherford backscattering and channelling experiments. Structural changes, the lattice site occupation of the implanted manganese atoms, static displacements of the lattice atoms, the ion implantation-induced reduction of grain size and the accumulation of strain could be directly observed as a function of manganese concentration. For the LNT implants it was found that at low manganese concentrations (i.e. less than 5 at.%) the impurities occupy mainly substitutional lattice sites ( f s ≅ 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 manganese impurity atoms are severely distorted. When the local manganese 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 manganese concentration c c for amorphization was found to be 8.5 at.% and the minimum volume v c of the amorphous clusters was found to be 2 × 10 −21 cm 3 which is the volume of a sphere with a radius of three interatomic distances. The RT implants showed a drastically reduced solubility, small lattice parameter changes and negligible homogeneous strains. Moreover, a non-zero amorphous fraction is observed at very small manganese concentrations, i.e. no threshold effect is observed in the amorphization curve. The differences of the amorphization process compared with the LNT case are discussed in terms of thermally activated short-range migration of manganese atoms which leads to the formation of amorphous clusters and to a relaxation of strains at lower manganese concentrations.