Effects of nuclear and electronic stopping powers on the conversion of hybrid silicate thin films

A study of the effects of nuclear and electronic stopping powers on the ion irradiation-induced conversion of hybrid silicate thin films is presented. The films were synthesized by sol-gel processing from a combination of tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and were spin-coated onto a Si substrate. After drying at 300 °C for 10 min, the films were irradiated with either 400 keV N2+ or 1 MeV Cu+ at fluences ranging from 1 × 1013 to 1 × 1016 ions/cm2. The ion species and energies were chosen such that electronic stopping powers were similar while nuclear stopping powers varied. The electronic and nuclear stopping powers of the ions in the films were calculated as a function of depth. The effects of stopping power on the film conversion were studied in terms of film shrinkage and nanomechanical response by utilizing atomic force microscopy and nanoindentation. Ion irradiation at lower fluences had a negligible effect on the hardness and reduced elastic modulus. However, after ion irradiation with a fluence of 1 × 1015 ions/cm2, the film irradiated with 1 MeV Cu+ had higher hardness and elastic modulus compared to the film irradiated with 400 keV N2+, suggesting the mechanical properties of the resulting thin films were related to both the electronic and nuclear stopping powers. After ion irradiation with a fluence of 1 × 1016 ions/cm2, the difference in the hardness and elastic modulus of the two irradiated films became smaller.