Initial stage growth of heteroepitaxial oxide thin films on oxide and metal substrates.

摘要

Complex oxide thin films have been extensively studied due to their versatile physical properties. The fabrication of epitaxial multilayered heterostructures based on complex oxides requires the ability to integrate these materials with desirable substrates with atomic layer control of the thin films. We have investigated the initial stage growth of heteroepitaxial oxide thin films on oxide and metal substrates, employing pulsed laser deposition (PLD) with in-situ high pressure reflection high energy electron diffraction (RHEED).; For the epitaxy of oxide-on-oxide, Sr1- xCaxRuO3 oxides ( x = 0, 0.5, and 1) were chosen as a model system and grown on four different oxide substrates with varying lattice misfits from -1.92% tensile to +3.64% compressive. Our study showed systematic changes in growth modes, growth morphologies, and strain relaxation as a function of lattice misfits (&egr;). At the initial stage, Sr1- xCaxRuO3 thin films had growth mode transitions from 2-dimensional (2D) layer-by-layer to step-flow (&egr; 1%) or 3D islands (&egr; ≥ 1%). In addition, termination conversion from B-site to A-site took place during the initial stage growth of Sr1-xCaxRuO 3 thin films on TiO2-terminated (001) SrTiO3 substrates.; For the epitaxy of oxide-on-metal, oxide buffer layers such as SrTiO 3, CaTiO3, CeO2, and Y2O3 were grown on epitaxial (001) Ni thin films. It was shown that initial stage growth of the oxide buffer layers strongly depended on the surface structures of the (001) Ni surfaces. Purely epitaxial oxide buffer layers could be achieved only on the c(2 x 2)-O reconstructed (001) Ni surface which was formed from a dissociation of water vapor in a forming gas environment. In contrast, growth on textured NiO surfaces or clean Ni surfaces produced textured oxide thin films with multi-domains.; Understanding the initial stage growth of epitaxial oxide thin films on both oxide and metal substrates was essential in achieving smooth, high-quality epitaxial thin films. Our findings will also provide the guideline in the atomic scaled control in the epitaxial oxide heterostructure devices such as oxide based magnetic tunnel junctions and YBa2Cu3O 7 coated conductors.