Ion track formation below 1Â MeV/u in thin films of amorphous SiO2

The evolution of pore diameter and etch yield were studied as a function of energy for each ion species. The track etching threshold in the electronic stopping power (dE/dx)e and specific energy was found to be approximately 1.5 keV/nm and 0.04 MeV/u, respectively, which is lower than previously observed. In a transition regime, 1.5 keV/nm < (dE/dx)e < 4.0 keV/nm, etching yields were less than 100%. For (dE/dx)e > 4.0 keV/nm all tracks were revealed, i.e. etching efficiency was 100%, corresponding to continuous tracks. Above the etching threshold the pore diameter increased with energy and (dE/dx)e for each ion species, and attained a maximum value before the electronic stopping power maximum of the respective ion was reached.