Impact of surfactants on electrical conduction and preferred orientation of spray-pyrolysed nanostructured SnO2 thin films for LPG and ammonia sensing

Abstract

SnO2 nanostructured thin films by spray pyrolysis technique have been successfully synthesised with surfactants isopropyl alcohol (IPA) and sodium dodecyl sulphate (SDS) independently. The effect of surfactants on the structural, and morphological properties of SnO2 films are investigated by different techniques such as X-ray diffraction, field emission scanning electron microscopy, and high resolution transmission electron microscopy. The deposited tetragonal rutile-phased SnO2 thin films are benefited by morphological modifications along with grain size reduction on changeover of IPA to SDS in the precursor. The sensing properties of the samples are investigated for LPG and NH3 at different operating temperatures. For a concentration of 500 ppm, the SDS employed film shows a maximum response of 96.7% for LPG and 86.8% for ammonia, at an operating temperature of 350 °C. By using SDS, the LPG sensing temperature could be lowered to 200 °C. The charge transport in the films is analysed by studying the dc and ac electrical conduction and a feasible mechanism has been envisaged in relation to the enhanced sensing characteristics of the films. By studying the dielectric constant variation with frequency and by analysing the exponent factor change, it is confirmed that multi-hopping process is responsible for conduction in the films.