Synthesis of sol-gel films

The films were synthesized through a sol-gel method, as previously described⁵. A mixture of 7.5 mol ethanol, 1 mol distilled water, and 1 mol acetic acid was stirred at room temperature in a beaker, followed by sequential addition of 0.6 mol methyltriethoxysilane (MTES) and 0.4 mol tetraethylorthosilicate (TEOS), drop by drop under vigorous stirring. The solution was stirred for 10 min before adding 0.25 mol polyvinylpyrrolidone (PVP). The mixture temperature was then raised to 50 °C and kept at this temperature for 30 min. Prior to deposition, the sol was stored for 24 h in an argon atmosphere and was then spin-coated onto a polished (100) silicon wafer. The films were dried at 80 °C and heat-treated at 300 °C in air for 30 mins. The film thickness was measured by a step height technique using an atomic force microscope. The thickness of the films after deposition was close to 1000 nm, and ranged from 200 nm to 1000 nm after ion irradiation.