Epitaxial optimization of atomically smooth Sr3Al2O6 for freestanding perovskite films by molecular beam epitaxy

Abstract The epitaxial crystal quality of strontium aluminate (Sr3Al2O6) films under various Sr/Al ratios were systematically investigated by reactive molecular beam epitaxy. Efficient guiding rules for real-time optimization are summarized that a four-fold reconstructed reflection high-energy electron diffraction (RHEED) pattern and 4 periods of RHEED oscillations coinciding in the growth of one unit cell of Sr3Al2O6 is the key signature for the optimal growth condition. Following above rules, atomically smooth Sr3Al2O6 and freestanding SrTiO3 films with a full width at half maximum less than 0.03∘ (mainly limited by the substrates) were synthesized. The high-crystalline quality of freestanding SrTiO3 and atomically smooth interface between SrTiO3 film and Sr3Al2O6 were highlighted by the appearance of well-defined fringes from X-ray diffraction data and well-organized atomic distribution from electron microscopy. The epitaxial optimization of Sr3Al2O6 buffer layer with atomic flatness and high-crystalline quality will shed light on the synthesis of ultrathin freestanding oxide perovskite films, paving the way to the exploration of incorporating strongly correlated properties in conventional semiconductors for a generation of multifunctional electronic devices.