Thermal stability of SrFeO3/Al2O3 thin films: Transmission electron microscopy study and conductometric sensing response

The SrFeO3/Al2O3 thin film system has been studied using transmission electron microscopy (TEM). The thin films of SrFeO3 were grown by pulsed laser deposition onto single crystal and sintered polycrystalline Al2O3 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 SrAl2−xFexO4 and SrFe12−yAlyO19. Evaluation for thin film conductometric sensing applications indicated that the untreated films deposited at 700 °C onto both single crystal and sintered Al2O3 substrates exhibited a p-type gas sensor response to oxygen at 500 °C.