Anomalous triple junction surface pits in nanocrystalline zirconia thin films and their relationship to triple junction energy

Triple junctions (TJs) are the lines where three grains or grain boundaries meet and become increasingly important in nanocrystalline materials where they have a high areal number density and occupy a significant fraction of the total volume of the material. Surface pits are associated with TJs, just as surface grooves are associated with grain boundaries, and these pits may have particularly deleterious effects on the behaviors of thin films. We evaluate the surface topography associated with TJs in nanocrystalline ZrO2 thin films using thickness mapping images produced by energy-filtered transmission electron microscopy (EFTEM), and compare our results with theoretical predictions. While many of the pits conform to the standard theoretical treatment, some of them exhibit considerably increased depth, possibly indicating that the junctions have line energy. No pits were observed with less than the theoretically predicted depth.