Atomic scale oxide superlattices grown by RHEED controlled pulsed laser deposition

Abstract

By depositing thin films under conditions where intensity oscillations are observed in RHEED (reflection high-energy electron diffraction) spots, unit cell level multilayers of SrTiO3/BaTiO3 structures have been grown by pulsed laser ablation. High resolution TEM (transmission electron microscopy) and STEM (scanning transmission electron microscopy) observations of the deposits show that epitaxial multilayers with layer thicknesses of 1, 2, 4, 8, and 16 unit cells can be grown on [100] orientation SrTiO3 substrates. The superlattices show partial intermixing of the Sr and Ba for layer thicknesses less than 8 unit cells, but incomplete intermixing occurs even when the layers are only a single unit cell thick. From observations of the degree of intermixing at different depths in the deposit, it was determined that most of the intermixing takes place during deposition and not during subsequent annealing of the deposit. The 16 and 8 unit cell thick BaTiO3 layers were found 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 SrTiO3 layers.