  We present an investigation of the near-surface tetragonal phase transition
in SrTiO3, using the complementary techniques of beta-detected nuclear magnetic
resonance and grazing-incidence X-ray diffraction. The results show a clear
depth dependence of the phase transition on scales of a few microns. The
measurements support a model in which there are tetragonal domains forming in
the sample at temperatures much higher than the bulk phase transition
temperature. Moreover, we find that these domains tend to form at higher
temperatures preferentially near the free surface of the crystal. The details
of the tetragonal domain formation and their depth/lateral dependencies are
discussed.
