Effect of long term ageing under humid environment on the LPG sensing properties and the surface composition of Mg-doped SnO2 thin films

Abstract

Pure and Mg-doped SnO2 films are prepared through a spray pyrolysis reaction, wherein the light doping keeps up the tetragonal rutile SnO2 polycrystalline structure. When the compositional ratio of Mg:SnO2 is 0.6wt%, the obtained crystallites have a size of 36nm and show the highest response of 93% in 1000ppm LPG, which is nearly three times larger than that of undoped SnO2. Storage under humid atmospheric conditions influences the gas response of tin oxide thin film sensors. To analyze the cause, the morphology, microstructure and composition of the films are studied in relation to the gas response of the film, with a collection on films having maximum sensitivity. It is observed that a thin surface coverage of hydroxyl groups is developed during storage at room atmosphere to cause an increase in resistance and a decline in gas response. Argon-ion etching or annealing of the samples in atmospheric air largely removes the morphological changes in the aged film surface. It has been observed that annealing of the film at the deposition temperature facilitates to go back to the initial response value.