Nanoscale density fluctuations in swift heavy ion irradiated amorphous SiO ₂

We report on the observation of nanoscale density fluctuations in 2 m thick amorphous SiO ₂ layers irradiated with 185 MeV Au ions. At high fluences, in excess of approximately 5 10 ¹² ionscm ², where the surface is completely covered by ion tracks, synchrotron small angle x-ray scattering measurements reveal the existence of a steady state of density fluctuations. In agreement with molecular dynamics simulations, this steady state is consistent with an ion track annihilation process, where high-density regions generated in the periphery of new tracks fill in low-density regions located at the center of existing tracks.