Nanocrystalline SnO2:F Thin Films for Liquid Petroleum Gas Sensors

Abstract

This paper reports the improvement in the sensing performance of nanocrystalline SnO₂-based liquid petroleum gas (LPG) sensors by doping with fluorine (F). Un-doped and F-doped tin oxide films were prepared on glass substrates by the dip-coating technique using a layer-by-layer deposition cycle (alternating between dip-coating a thin layer followed by a drying in air after each new layer). The results showed that this technique is superior to the conventional technique for both improving the film thickness uniformity and film transparency. The effect of F concentration on the structural, surface morphological and LPG sensing properties of the SnO₂ films was investigated. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films are nanocrystalline SnO₂ with nanoscale-textured surfaces. Gas sensing characteristics (sensor response and response/recovery time) of the SnO₂:F sensors based on a planar interdigital structure were investigated at different operating temperatures and at different LPG concentrations. The addition of fluorine to SnO₂ was found to be advantageous for efficient detection of LPG gases, e.g., F-doped sensors are more stable at a low operating temperature (300 °C) with higher sensor response and faster response/recovery time, compared to un-doped sensor materials. The sensors based on SnO₂:F films could detect LPG even at a low level of 25% LEL, showing the possibility of using this transparent material for LPG leak detection.