Takahisa Yamamoto

The topological and morphological changes of the (001) surface of single‐crystal (La 0.3 Sr 0.7 )(Al 0.65 Ta 0.35 )O 3 during treatment with high‐purity deionized water (DI) have been investigated by atomic force microscopy and scanning transmission electron microscopy (STEM). Etching by DI treatment at room temperature proceeded mainly in anisotropic etching mode, resulting in rectangular etch pits with {001} inner surfaces forming in the surface. The dominant etching mode changed from anisotropic to isotropic with increasing DI‐treatment temperature, and the lowest surface roughness occurred for DI treatment at 50°C for 60 min. Direct observation of the atomic structure of the surface by STEM showed that the etched surface was the B‐site‐terminated (001) surface after anisotropic etching at 50°C for 60 min, in which the B‐site‐terminated atomic layer was found to maintain the B‐site ordered structure existing in the crystal. This is because DI treatment, which does not require high‐temperature heat treatment of the substrate, suppresses element diffusion, sublimation, and formation of point defects on and in the vicinity of the surface.