F-doped nanocrystalline SnO2 thin films for liquid petroleum gas (LPG) sensors

In this paper we reported the improvement sensing performance of nanocrystalline SnO₂ thin film based LPG sensors by doping with fluorine. Un-doped and F-doped tin oxide films were prepared on glass substrates by 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. Atomic Force Microscopy (AFM) and X-ray diffraction pattern measurements showed that the obtained thin films were nanocrystalline SnO₂. Gas sensing characteristics (sensor response, response/recovery time and repeatability) of the nanocrystalline SnO₂ sensors based on a planar interdigital structure were investigated at different operating temperatures and 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 were more stable at low operating temperature and had higher sensor response and faster response/recovery time, compared to un-doped sensor material.