  Perovskite oxides attract increasing attention due to their broad potential
in many applications. Understanding their surfaces is challenging, though,
because the ternary composition of the bulk allows for multiple stable surface
terminations. We demonstrate a simple procedure for preparing the
bulk-terminated (001) surface of SrTiO3, a prototypical cubic perovskite.
Controlled application of strain on a SrTiO3 single crystal results in a flat
cleavage with micrometer-size domains of SrO and TiO2. Distribution of these
two terminations is dictated by ferroelectric domains induced by strain during
the cleavage process. Atomically-resolved scanning tunneling microscopy/atomic
force microscopy (STM/AFM) measurements reveal the presence of point defects in
a well-defined concentration of (14+-2)%; Sr vacancies form at the SrO
termination and complementary Sr adatoms appear at the TiO2 termination. These
intrinsic defects are induced by the interplay between ferroelectricity,
surface polarity, and surface charge.
