AVS 53rd International Symposium
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP3
Unexpected Growth Modes for Heteroepitaxial BaTiO@sub 3@ Films Due to Kinetic Limitation

Tuesday, November 14, 2006, 6:00 pm, Room 3rd Floor Lobby

Session: Surface Science Poster Session
Presenter: J. Shin, The University of Tennessee
Authors: J. Shin, The University of Tennessee
A.Y. Borisevich, Oak Ridge National Laboratory
S.V. Kalinin, Oak Ridge National Laboratory
E.W. Plummer, The University of Tennessee
A.P. Baddorf, Oak Ridge National Laboratory
Correspondent: Click to Email
Fully strained BaTiO@sub 3@ (BTO) films have the strongest polarization because the c/a ratio is maximized. However, epitaxial growth of BTO films on SrTiO@sub 3@ (STO) is very difficult in oxygen pressures above 1 mTorr due to a large lattice mismatch (2.28%) and the Stranski-Krastanov (SK) growth mode with lattice relaxation is likely. To avoid the formation of 3D islands and prevent the system from reaching equilibrium, kinetic limitations can be used to reduce the surface diffusion length by changing the growth rate or the growth temperature. BTO films grown on (001)STO substrates by pulsed laser deposition have been investigated as a function of growth temperature and growth rate by atomic force microscopy, x-ray diffraction, reflection high energy electron diffraction, and transmission electron microscopy (TEM). The 125 nm thick BTO films deposited using the relatively high average growth rate (0.2 ML/s) with 10 mTorr oxygen pressure exhibit layer-by-layer or layer-then pseudo 2D island growth modes with increasing temperature, which is also related to thermal expansion differences between films and substrate. Compared with low growth rate (0.08 ML/s) condition, which shows conventional SK growth above 1 mTorr oxygen, this high growth rate condition provides 125 nm thick BTO films that are highly strained with visible terraces. In addition to the conventional layer-by-layer mode, an unusual pseudo 2D island growth mode is observed above 1050 K, where islands of several unit cell heights are observed between single height film steps. These islands are nearly steady-state; once formed, the film roughness does not increase with thickness as it does for 3D islands, and the island size and density remains fixed, with evidence of island-island repulsion. Pseudo 2D island growth appears related to the lattice of film dislocations observed with TEM. Research sponsored by Office of BES, U.S. DOE, under contract DE-AC05-00OR22725 with ORNL, managed by UT-Battelle, LLC.