Indication of thermal roughening in the retrieved mean inner potential across a Σ5 grain boundary in SrTiO<inf>3</inf> annealed at different temperatures

We have measured the mean inner potential depth at a Σ5 grain boundary in a SrTiO3 bicrystal by reconstructing the exit-face wave function from an image focal series collected by transmission electron microscopy. We find that, as the annealing temperature increases, the potential depth at the grain boundary exponentially increases. We interpret the temperature dependence of the potential depth as the signature of a grain-boundary thermal roughening transition.