  We report that a deionized water etching and thermal annealing technique can
be effective for preparing atomically-flat and singly-terminated surfaces of
single crystalline SrTiO3 substrates. After a two-step thermal-annealing and
deionized-water etching procedure, topography measured by atomic force
microscopy shows the evolution of substrates from a rough to step-terraced
surface structure. Lateral force microscopy confirms that the atomically-flat
surfaces are singly-terminated. Moreover, this technique can be used to remove
excessive strontium oxide or hydroxide composites segregated on the SrTiO3
surface. This acid-etchant-free technique facilitates the preparation of
atomically-aligned SrTiO3 substrates, which promotes studies on two-dimensional
physics of complex oxide interfaces.
