Deposition Rate Effect on Critical Thickness of BaTiO 3 Epitaxial Thin Film Grown on SrTiO 3 (001)
- PDF / 1,353,159 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 86 Downloads / 244 Views
1034-K10-04
Deposition Rate Effect on Critical Thickness of BaTiO3 Epitaxial Thin Film Grown on SrTiO3 (001) Masanori Kawai1, Daisuke Kan1, Seiichi Isojima1, Hiroki Kurata1, Seiji Isoda1, Shigeru Kimura2, Osami Sakata2, and Yuichi Shimakawa1 1 Institute for Chemical Research, Kyoto University, Gokasyo, Uji, Kyoto, 611-0011, Japan 2 JASRI/SPring-8, 1-1-1 Kouto, Mikazuki, Sayo-gun, Hyogo, 679-5198, Japan ABSTRACT BaTiO3/SrTiO3(001) epitaxial thin films were prepared at various growth rates by pulsed laser deposition, and their heterostructures were evaluated by synchrotron x-ray diffraction measurements and cross-sectional scanning transmission electron microscopy observations. In a film grown at a low deposition rate (0.01 nm/s), misfit dislocations are found near the interface and a fully relaxed BaTiO3 thin film grows epitaxially on the substrate. On the other hand, a film grown at a high deposition rate (0.04 nm/s) consists of strained and relaxed BaTiO3 lattices. Our results showed that the critical thickness of BaTiO3/SrTiO3(001) epitaxial thin films can be controlled by the deposition rate and that the critical thickness increases with increasing the deposition rate, and by adjusting the deposition rate we were able to prepare epitaxial thin films consisting of fully strained BaTiO3, partially strained BaTiO3 or fully relaxed BaTiO3. We have also achieved the growth controlling of BaTiO3 thin films on SrTiO3(001) substrates with SrRuO3 bottom electrode layer. INTRODUCTION Defect engineering for ferroelectric thin films have attracted a great deal of interest because strain fields and dislocations crucially affect the ferroelectric or leakage properties of the thin films [1-3]. BaTiO3 (BTO) is one of the most extensively studied materials among such studies. It has a perovskite structure and a bulk sample shows ferroelectricity below TC = 408 K. The BTO material can grow epitaxially on a perovskite SrTiO3(STO)(001) substrate. Since its in-plane lattice constant at a growth temperature is larger than that of STO(001), there is a lattice mismatch between BTO and the STO(001) substrate. BTO thin films therefore usually grow on the STO(001) substrates as the following manner. BTO initially grows on STO(001) in a 2-dimensional (2D) layer-by-layer Frank-van der Merwe (FM) mode [4] and the lattice mismatch is compensated by compressive strain. The strain causes structural distortion that elongates the BTO lattice along the out-of-plane direction. Beyond the critical thickness, at which misfit dislocations relax the strain, BTO grows in the 3D Volmer-Weber (VW) mode [5]. Such misfit dislocations and the strain fields around the defects often cause considerable effects on physical properties of the grown thin films [2]. Indeed, the strained BTO films show the enhanced ferroelectric properties [3,6]. There are many reports on the critical thickness of epitaxial BTO thin films grown on STO(001) substrates. Critical thicknesses calculated from elastic energy consideration by using the Matthew’s formulation [7] range from 2
Data Loading...
