Surface quality improvement of porous thin films suitable for nanoindentation

The reliability of perovskite material La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) to be used as cathode parts in solid oxide fuel cells (SOFCs) also relies on its mechanical properties. Adequate surface conditions (i.e. flat and crack-free) are desired when the as-sintered porous thin films are subjected to nanoindentation for mechanical property determination. In this study, extensive cracks and considerable surface roughness were found in the LSCF films after sintering at high temperatures. This would significantly scatter the nanoindentation data and results in unreliable measurements. Various attempts including the comparison of film deposition methods, drying and sintering processes, and reformulating the ink were made to improve the surface quality. Results revealed little dependence of cracking and surface roughness on deposition methods, drying and sintering processes. It was found that the critical factor for obtaining crack-free and smooth LSCF films was the ability of the ink to be self-leveling in the earlier wet state. Reproducible nanoindentation measurements were obtained for the films with improved surface quality.