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

Only a few studies have so far been reported on ion track formation using low energy ion beams. Therefore we have performed a systematic study using different heavy ions at energies below 1 MeV/u for irradiation of thin films of amorphous silicon dioxide (a-SiO2). The induced latent ion tracks were studied by selective chemical etching in an aqueous HF solution and the resulting pores were investigated by scanning electron microscopy. 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