Faceting of single-crystal SrTiO₃ during wet chemical etching

We use an Atomic Force Microscope (AFM) to study changes in the surface of single-crystal SrTiO₃ etched in HF-based solutions. Attention in this work has been focused upon observations of pyramidal pitting - both because of an interest in avoiding etch pits during substrate preparation prior to heteroepitaxial growth, and because of an interest in micromachining this highly polarizable material. We note that (110) SrTiO₃ is surprisingly robust against the formation of pits, while pitting is significant on (100) surfaces. Particular etch rates have been measured, and we discuss anisotropies in the rates of dissolution. These data are combined to extract a macroscopic model describing processes relevant to the most extreme pitting, which we show to be associated with surface defects.