Evolution of nanotracks in silicon nitride under intense electronic excitation: Role of H evolution and a concomitant dynamic electronic energy loss

Exposure to intense electronic excitation in PECVD-grown amorphous hydrogenated silicon nitride (a-SiNx:H) thin films with 100 MeV Ni7+ results in the formation of continuous nanoscale ion track structures at the lower fluence of 5 × 1012 ions/cm2, whereas at the higher fluence of 1 × 1014 ions/cm2, the track structures fragment into discontinuous ion track-like structures. Concomitantly, the diameter of the ion tracks is also found to increase with fluence. The observation of the discontinuous ion track-like structures at the high fluence of 1 × 1014 ions/cm2 suggests 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 (Se) during the course of irradiation and a continuously evolving density resulting from the out-diffusion of hydrogen from the a-SiNx:H films. The proposed mechanism of ion track evolution is supported by the thermal spike simulations.