Thermal stability of SrFeO 3 / Al 2 O 3 thin films: Transmission electron microscopy study and conductometric sensing response

The SrFeO 3 / Al 2 O 3 thin film system has been studied using transmission electron microscopy (TEM). The thin films of SrFeO 3 were grown by pulsed laser deposition onto single crystal and sintered polycrystalline Al 2 O 3 substrates at room temperature (RT) and 700 ° C and subjected to annealing for various periods of time at 700 - 1000 ° C . TEM characterization showed that the morphology of the film varied with changes of deposition temperature. Films deposited at RT featured a columnar structure and those deposited at 700 ° C showed layers with crystalline grains. The interfacial structures of the films remained unchanged below 700 ° C . Interfacial reactions were observed following annealing at 850 ° C for 5 h. The phase transformation at the interface was characterized for the film annealed at 1000 ° C for 5 h, for which the principal phases were identified as SrAl 2 − x Fe x O 4 and SrFe 12 − y Al y O 19 . Evaluation for thin film conductometric sensing applications indicated that the untreated films deposited at 700 ° C onto both single crystal and sintered Al 2 O 3 substrates exhibited a p -type gas sensor response to oxygen at 500 ° C .