  The ferroelectric domain pattern within lithographically defined
PbTiO3/SrTiO3 ferroelectric/dielectric heteroepitaxial superlattice
nanostructures is strongly influenced by the edges of the structures.
Synchrotron x-ray nanobeam diffraction reveals that the spontaneously formed
180{\deg} ferroelectric stripe domains exhibited by such superlattices adopt a
configuration in rectangular nanostructures in which domain walls are aligned
with long patterned edges. The angular distribution of x-ray diffuse scattering
intensity from nanodomains indicates that domains are aligned within an angular
range of approximately 20{\deg} with respect to the edges. Computational
studies based on a time-dependent Landau-Ginzburg-Devonshire model show that
the preferred direction of the alignment results from lowering of the bulk and
electrostrictive contributions to the free energy of the system due to the
release of the lateral mechanical constraint. This unexpected alignment appears
to be intrinsic and not a result of distortions or defects caused by the
patterning process. Our work demonstrates how nanostructuring and patterning of
heteroepitaxial superlattices allow for pathways to create and control
ferroelectric structures that may appear counterintuitive.
