Evolution of ion track morphology in a-SiNx:H by dynamic electronic energy loss

Amorphous hydrogenated silicon nitride ($\textit{a}$-SiN$_\mathrm{\textit{x}}$:H) thin films irradiated with 100 MeV Ni$^{7+}$ results in the formation of continuous ion track structures at the lower fluence of $5\times{10^{12}}$ ions/cm$^2$ whereas at higher fluence of $1\times{10^{14}}$ ions/cm$^2$ the track structures fragment into discontinuous ion track like structures . The observation of the discontinuous ion track like structures at the high fluence of $1\times{10^{14}}$ ions/cm$^2$ shows clearly that higher fluence irradiation may not always lead to dissolution of the microstructure formed at lower fluence. The results are understood on the basis of a dynamic electronic energy loss (S$_{e}$) in the course of irradiation resulting from the out-diffusion of hydrogen from the films and a continuous increase in density of $\textit{a}$-SiN$_\mathrm{\textit{x}}$:H films.