STO/BTO Modulated Superlattice Multilayer Structures with Atomically Sharp Interfaces

A comparative study is carried out investigating the microstructure and the electrical properties of BaxSr1-xTiO3 films with x = (0.25, 0.5, 0.75) deposited as modulated superlattice (SL) multilayer structures by laser ablation on both LaAlO3 and MgO substrates. The SL structures are examined using high-resolution transmission electron microscopy and scanning transmission electron microscopy. Their interfaces and chemical composition are investigated using energy dispersive X-ray spectroscopy, complemented with electron energy loss spectra analysis performed to give insight to the local chemistry, structure and bonding. It is found that all modulated SL samples consisted of continuous well defined 1 nm SrTiO3 and 4 nm BaTiO3 layers. When modulated SL multilayered structures are compared with their single target deposited equivalents, they exhibit similar electrical properties (e.g. dielectric constant and dielectric loss) but undergo phase transition in a broader temperature region. A very important observation is that the oxygen K-edges in SrTiO3 and BaTiO3 layers are distinctive. Therefore it can be used as finger-print signature for analysis of ultra-thin SrTiO3/BaTiO3 layers and their interfaces. Finally it is demonstrated that by varying the modulation period it is possible to develop structures with engineered ferroelectric properties and improved thermal stability.