Thermal stability of strontium iron oxide/silicon dioxide/silicon and strontium iron oxide/aluminum oxide thin film systems: Transmission electron microscopy study of interfacial structures of the thin film systems and conductometric sensing response of strontium iron oxide/aluminum oxide.

摘要

The literature review indicates that studies on the structures and properties of perovskites materials have shown attractive applications in the fields of energy, catalysts and sensing materials for fuel cell and sensing industries. Kinetic phenomena in thin film systems, such as solid state amorphization and interface reactions due to diffusion during thin film deposition, are introduced indicating that thermal stability is a concern in thin film sensor device application. The principle of traditional methods of materials characterization is briefly discussed. Emphasis is placed on the functions of analytical transmission electron microscopy.;The films in the SrFeO3/Al2O3 system were deposited onto single crystal and sintered polycrystalline Al2O 3 substrates at room temperature 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 in deposition temperature: a columnar structure was produced at room temperature and layers containing crystalline grains were produced at 700°C. The interfacial structures of the films remained unchanged below 700°C. Interfacial reactions were observed following annealing at 850°C for 5 hours. The phase transformation at the interface was characterized for the film annealed at 1000°C for 5 hours, for which the principal phases were identified as SrAl2-xFe xO4 and SrFe12-yAlyO19. As a result, an isothermal section at 1000°C of a ternary phase diagram for SrO-Al2O3-Fe2O3 is proposed. 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 similar temperature dependency of conductivity in air and a p-type gas sensor response to oxygen and propane at 500°C.;The SrFeO3/SiO2/Si and SrFeO3/Al 2O3 thin film systems have been studied using transmission electron microscopy. The thin films of SrFeO3 were grown by pulsed laser deposition. For the SrFeO3/SiO2/Si system, TEM characterization showed that the microstructure of the film deposited at room temperature contained crystalline and amorphous layers. Silicon diffusion into SrFeO3 films occurred at the SiO2 interface. The silicon-induced interfacial reactions resulted in phase transformations and the growth of complex crystalline and amorphous phases. The principal compositions of these phases were Sr(Fe,Si)12O19, SrOx and amorphous [Sr-Fe-Si-O].