Initial Growth Stages of Epitaxial BaTiO 3 Films on Vicinal SrTiO 3 :Nb (001) Substrates
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Initial growth stages of epitaxial BaTiO3 films on vicinal SrTiO3:Nb (001) substrates A. Visinoiu, M. Alexe, H. N. Lee, D. N. Zakharov, A. Pignolet, D. Hesse, and U. Gösele Max Planck Institute of Microstructure Physics, D-06120 Halle (Saale), Germany.
ABSTRACT
The growth mechanism of epitaxial BaTiO3 films on vicinal Nb-doped SrTiO3 (SrTiO3:Nb) (001) substrate surfaces was studied in terms of surface morphology, crystalline orientation, microstructure, and film/substrate interface. Well-oriented BaTiO3 thin films were grown on SrTiO3 substrates with well-defined terraces by pulsed laser deposition. The regularly terraced TiO2-terminated surfaces of vicinal SrTiO3:Nb (001) substrates were prepared by a definite chemical and thermal treatment. Under our conditions, BaTiO3 seems to grow with a layer-then-island (Stranski-Krastanov) growth mechanism. In order to investigate the orientation and crystallinity of the BaTiO3 films, x-ray diffraction and high-resolution transmission electron microscopy were performed. Ferroelectricity of the BaTiO3 films was proved by electrical measurements performed on Pt/BaTiO3/SrTiO3:Nb heterostructures.
INTRODUCTION
BaTiO3 is considered to be the prototype of perovskite ferroelectrics [1]. Considerable attention has been given to the properties of grown films explaining them in terms of advanced growth, while the initial stages of film growth and the growth mechanisms are so far not studied in detail. The classical theory of film growth distinguishes three growth mechanisms: layer-bylayer growth (Frank-van-der Merwe), island growth (Volmer-Weber), and layer-then-island growth (Stranski-Krastanov), depending on the surface energies of film and substrate, as well as of the film/substrate interface energy [2]. Pulsed laser deposition (PLD) has become an important technique to produce highquality multicomponent thin films including ferroelectric, high-temperature superconducting, electro-optic, and optical films [3]. The growth of BaTiO3 films by PLD on different substrates has been observed to follow different mechanisms, e.g. layer-by-layer growth on SrTiO3 (001) [4], island growth on MgO (001) [5]. Layer-by-layer growth has been reported to be a possible growth mechanism by theoretical electronic structure calculations taking into account the surface charge neutrality [6]. This paper presents an experimental study of initial stages of the epitaxial BaTiO3 film growth on SrTiO3 (001) substrates by PLD. Our motivation for this work is a better understanding of the initial growth mechanism of BaTiO3 (tetragonal: a = b = 3.994 Å and c = 4.038 Å) films. SrTiO3 (cubic: ac = 3.905 Å) substrates have been chosen because of the low lattice mismatch (afilm - asubstrate) / asubstrate = 2.28%. This work is to be considered in the general frame of improvement of the dielectric properties of BaTiO3 films by replacing them with BaTiO3/SrTiO3 superlattices [7]. C8.4.1 Downloaded from https://www.cambridge.org/core. Access paid by the UCSB Libraries, on 26 Mar 2018 at 03:13:33, subject to the Cambri
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