Excimer laser processing of nanostructured SnO2 thin films and its impact on LPG sensing

Abstract

KrF excimer laser (λ = 248 nm) has been employed to anneal nanocrystalline Tin oxide (SnO2) films deposited at 200 °C using spray pyrolysis. With the increase of irradiation laser fluence, the film crystallinity has been improved while the matrix stress decreased along all the crystal planes except (110) and (301), for an energy density of 150 mJ/cm2 as compared to non-irradiated films. The maximum liquid petroleum gas (LPG) response observed for a fluence 150 mJ/cm2 is 92.6% at 350 °C whereas a response is 4% at the onset sensing temperature of 100 °C. Moreover, the response and recovery times have also improved by the laser processing and the cross sensitivity for NH3 and NO2 gases are in a desirable range. FESEM images of irradiated films show polygonal shaped distributions of aggregated nanocrystalline particle-clusters with grain boundaries and nanovoids. XPS shows oxygen deficient lattice besides surface and/or pore-bound oxygen contributions. Raman analyses confirm the sub-stoichiometric SnO2-x phases and a high concentration of defects such as oxygen vacancies (OVs) on surface sites. Based on these observations, the gas sensing mechanism is discussed in brief.