The effect of aluminium concentration on the resistance of Si3N4 to ion track formation

The role of Al impurities on the structural response of polycrystalline silicon nitride to swift Xe and Bi ions at single ion track and overlapped ion track fluences is investigated. Si3N4 with Al impurity concentrations of 3 at. %, 1 at.% and 0.1. at.% were examined by means of high resolution scanning transmission electron microscopy. The threshold electronic energy loss (Set) required to form amorphous tracks was found to decrease with increasing Al fraction from above 33 keV/nm (0.1 at.% Al) to below 22 keV/nm for specimens containing about 3 at.% Al. All specimens were partially amorphized at overlapping ion fluence and the amorphous fraction monotonically increased with increasing Al content at the same ion fluence.