Crystallinity and Surface Morphology of Epitaxial (Sr,Ba)Nb2O6 Thin Film Prepared by Pulsed Laser Deposition with Two-Step Growth Sequence

Abstract

AbstractWe have prepared epitaxially grown SBN thin film with c-axis orientation by an ArF pulsed laser deposition on SrTiO3(100). Pole figures show that the SBN film has a twin structure aligned at ±18.4: with the a-axis of SrTiO3. The epitaxial relationship of SBN<310> //SrTiO3 < 100 > is determined. The lattice mismatch between SBN and SrTiO3 is approximately 0.9%, which contributes to the desirable crystallinity of the SBN thin film. Furthermore, we have tried to form the SBN film with a two-step growth sequence in order to improve surface morphology. The amorphous initial growth region of 5 monolayers (2 nm thickness) is prepared with no substrate heating followed by post-annealing treatment at 720°C and additional growth on the initially crystallized layer. RHEED patterns of the SBN film with the two-step growth sequence have remained streaky throughout the film formation, compared with spotty patterns observed from films prepared by a conventional sequence. Atomic force microscope (AFM) images show that both the initial stage and final stage have extremely flat surfaces of rms≦ lnm which is a remarkably improved figure compared with the roughness rms ≧3nm for the film deposited at 720°C from the initial stage. These results suggest that the two-step growth sequence makes it possible to improve surface morphology to a nanometer level.