  We investigated with synchrotron x-ray diffraction and reflectometry the
formation of structural domains in the near-surface region of single
crystalline SrTiO3 (001) substrates with Y0.6Pr0.4Ba2Cu3O7 / La2/3Ca1/3MnO3
superlattices grown on top. We find that the antiferrodistortive
cubic-to-tetragonal transition, which occurs at T_STO = 104K in the bulk and at
a considerably higher temperature of at least 120K in the surface region of
SrTiO3, has only a weak influence on the domain formation. The strongest
changes occur instead in the vicinitiy of the tetragonal-to-orthorhombic
transition in SrTiO3 around 65K, where pronounced surface facets develop that
reach deep (at least several micrometers) into the SrTiO3 substrate. These
micrometer-sized facets are anisotropic and tilted with respect to one another
by up to 0.5deg along the shorter direction. Finally, we find that a third
structural transition below 30K gives rise to significant changes in the spread
of the c-axis parameters. Overall, our data provide evidence for a strong
mutual interaction between the stuctural properties of the SrTiO3 surface and
the multilayer grown on top.
