Growth of Nanoscale BaTiO3/SrTiO3 Superlattices by Molecular-Beam Epitaxy

摘要

Commensurate BaTiO3/SrTiO3 superlattices were grown by reactive molecular-beam epitaxy on four different substrates: TiO2-terminated (001) SrTiO3, (101) DyScO3, (101) GdScO3, and (101) SmScO3. With the aid of reflection high-energy electron diffraction (RHEED), precise single-monolayer doses of BaO, SrO, and TiO2 were deposited sequentially to create commensurate BaTiO3/SrTiO3 superlattices with a variety of periodicities. X-ray diffraction (XRD) measurements exhibit clear superlattice peaks at the expected positions. The rocking curve full width half-maximum of the superlattices was as narrow as 7 arc s (0.002 deg). High-resolution transmission electron microscopy reveals nearly atomically abrupt interfaces. Temperature-dependent ultraviolet Raman and XRD were used to reveal the paraelectric-to-ferroelectric transition temperature (TC). Our results demonstrate the importance of finite size and strain effects on the TC of BaTiO3/SrTiO3 superlattices. In addition to probing finite size and strain effects, these heterostructures may be relevant for novel phonon devices, including mirrors, filters, and cavities for coherent phonon generation and control.