Influence of the nanostructural characteristics on the gas sensing properties of pulsed laser deposited tin oxide thin films

Tin oxide (SnO2) thin films doped with ∼2 at.% Pt have been deposited onto alumina substrates by reactive pulsed laser ablation of a pure SnO2 target in an oxygen atmosphere. At a KrF laser intensity of 5×108 W/cm2 and a substrate deposition temperature (Td) of 300 °C, the pulsed laser deposition (PLD) of SnO2 thin films was investigated under various oxygen background pressures (P(O2)) ranging from 1 to 200 mTorr. While all the deposited films consist of pure polycrystalline SnO2 phase, their mean grain size and nanoporosity, as deduced from TEM observations, were found to be highly influenced by P(O2). Indeed, the size of the nanograins that compose the SnO2 columns was found to increase from ∼4 nm for P(O2)≤100 mTorr to about 10 nm for P(O2)≥150 mTorr. The SnO2 films deposited under P(O2)≥100 mTorr are shown to exhibit an open inter-columnar porosity, while those grown under P(O2)=50 mTorr are characterized by randomly distributed spherical nanopores (∼1 nm). The deposited PLD SnO2 films were integrated into gas-sensing devices and their sensing performance was evaluated for CO gas concentrations ranging from 10 to 250 ppm in synthetic air. It is pointed out that the gas sensitivity of PLD SnO2 films, having grain size in the (3–10 nm) range, is predominantly influenced by the porosity of the nanostructure.