  Advances in synthesis techniques and materials understanding have given rise
to oxide heterostructures with intriguing physical phenomena that cannot be
found in their constituents. In these structures, precise control of interface
quality, including oxygen stoichiometry, is critical for unambiguous tailoring
of the interfacial properties, with deposition of the first monolayer being the
most important step in shaping a well-defined functional interface. Here, we
studied interface formation and strain evolution during the initial growth of
LaAlO3 on SrTiO3 by pulsed laser deposition, in search of a means for
controlling the atomic-sharpness of the interfaces. Our experimental results
show that growth of LaAlO3 at a high oxygen pressure dramatically enhances
interface abruptness. As a consequence, the critical thickness for strain
relaxation was increased, facilitating coherent epitaxy of perovskite oxides.
This provides a clear understanding of the role of oxygen pressure during the
interface formation, and enables the synthesis of oxide heterostructures with
chemically-sharper interfaces.
