ATOMIC-SCALE OXIDE SUPERLATTICES GROWN BY RHEED CONTROLLED PULSED-LASER DEPOSITION

By depositing thin films under conditions where intensity oscillations are observed in RHEED (reflection high-energy electron diffraction) s pots, unit cell level multilayers of SrTiO3/BaTiO3 structures have bee n grown by pulsed laser ablation. High resolution TEM (transmission el ectron microscopy) and STEM (scanning transmission electron microscopy ) observations of the deposits show that epitaxial multilayers with la yer thicknesses of 1, 2, 4, 8, and 16 unit cells can be grown on [100] orientation SrTiO3 substrates. The superlattices show partial intermi xing of the Sr and Ba for layer thicknesses less than 8 unit cells, bu t incomplete intermixing occurs even when the layers are only a single unit cell thick. From observations of the degree of intermixing at di fferent depths in the deposit, it was determined that most of the inte rmixing takes place during deposition and not during subsequent anneal ing of the deposit. The 16 and 8 unit cell thick BaTiO3 layers were fo und to be tetragonal with the c-axis of the layers oriented normal to the substrate but with the a-axis strained to coherently match the SrT iO3 layers.