Impact of annealing and soft template concentration on optical and sensing properties of wet-deposited SiO2 thin films

Abstract

The present study demonstrates deposition of porous SiO2 thin films using combination of sol-gel, soft-templating and spin-coating methods. The recipe for Si-sol using TEOS (tetraethylorthosilicate) as a precursor was optimized in order transparent and stable sol to be obtained. Commercially available triblock co-polymer Pluronic 123 was considered as a soft template and its concentration and volume fraction to sol were varied. For achieving the final composition of silica films, different stepwise annealing regimes were implemented where the temperatures and duration of each step were optimized. Optical properties of films were calculated using nonlinear curve fitting of measured reflectance spectra in UV-VIS spectral range. Surface morphology and structure of the films were characterized by Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED). The porosity and optical sensing ability of the films were tested by measurement of their reflectance spectra prior to and during exposure to acetone vapors which served as probe molecules. The influence of soft template composition and annealing regimes on SiO2 properties were revealed and application of studied films as sensitive media for opto-chemical sensing was discussed.