Amorphization mechanisms in ion implanted metal films and single crystals

Abstract

The mechanisms leading to amorphization due to high dose ion implantation into elemental thin films and single crystals are discussed. X-ray diffraction, Rutherford backscattering and channelling experiments show that the amorphization process in both substitutional and interstitial alloy systems exhibits similar features. At low impurity concentrations an accumulation of strains is observed due to the forced introduction of impurity atoms into the lattice of the target material. The strains are governed by the lattice site occupation of the impurity atoms, the atomic size mismatch between host and impurity and the local environment of the impurities. At a certain strain level and impurity concentration depending on the alloy system a sudden strain release coinciding with the onset of amorphization is observed. This behaviour is consistent with a theoretical amorphization model that treats the strains created by the introduction of foreign atoms into a lattice as the driving force for amorphization. The evolution of the amorphous phase over an extended region of impurity concentration is a result of the statistical distribution of impurities and local strains that lead to the formation of small amorphous clusters wherever the local impurity concentration and thus the local strains exceed a threshold value.