Controlling the growth of particle size and size distribution of silica nanoparticles by the thin film structure

Nanostructured silicondioxide thin films were prepared by sol–gel spin coating technique. The SiO2 films were made using a conventional mixture of tetraethoxysilane (TEOS), deionized water and ethanol with various NH3/TEOS ratios. The nanostructured silica films were made using a mixture of the SiO2 sol and regular SiO2 sol to control the enlargement of the particles inside the films. The structural, morphological and optical characterizations of the as-deposited and annealed films were carried out using X-ray diffraction (XRD), atomic force microscopy, scanning electron microscopy, NKD spectrophotometer and ultraviolet–visible (UV–vis) spectroscopy. The transmittance data of the infrared spectra of the films were recorded using an FT-IR Spectrometer. The XRD studies showed that as-deposited films were amorphous and the formation of the alfa-cristobalite phase of the silica film was investigated at annealing temperature close to 1,100 °C. Optical properties of the transmittance spectra in the s and p-polarization modes were collected. Refractive indices and extinction coefficients were determined with respect to the NH3/TEOS ratios in the compositions of the films. Optical cut-off wavelength values were investigated from the extrapolation of the absorbance spectra which was estimated from the UV–vis spectroscopy measurements. A red shift in the absorption threshold indicated that the size of silica nanoparticles was increased by an increase in the NH3/TEOS volume ratio from 1:64 to 1:8.