  Comparison between single- and the poly-crystalline structures provides
essential information on the role of long-range translational symmetry and
grain boundaries. In particular, by comparing single- and poly-crystalline
transition metal oxides (TMOs), one can study intriguing physical phenomena
such as electronic and ionic conduction at the grain boundaries, phonon
propagation, and various domain properties. In order to make an accurate
comparison, however, both single- and poly-crystalline samples should have the
same quality, e.g., stoichiometry, crystallinity, thickness, etc. Here, by
studying the surface properties of atomically flat poly-crystalline SrTiO3
(STO), we propose an approach to simultaneously fabricate both single- and
poly-crystalline epitaxial TMO thin films on STO substrates. In order to grow
TMOs epitaxially with atomic precision, an atomically flat, single-terminated
surface of the substrate is a prerequisite. We first examined (100), (110), and
(111) oriented single-crystalline STO surfaces, which required different
annealing conditions to achieve atomically flat surfaces, depending on the
surface energy. A poly-crystalline STO surface was then prepared at the optimum
condition for which all the domains with different crystallographic
orientations could be successfully flattened. Based on our atomically flat
poly-crystalline STO substrates, we envision expansion of the studies regarding
theTMOdomains and grain boundaries.
