Electron Microscopy Study Of Mocvd-Grown Tio 2 Thin Films and Tio 2 /Al 2 0 3 Interfaces
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ELECTRON MICROSCOPY STUDY OF MOCVD-GROWN TiO 2 THIN FILMS AND TiO2JA120 3 INTERFACES Y. Gao, K. L. Merkle, H. L. M. Chang, T. J. Zhang, and D. J. Lam Materials Science Division, Argonne National Laboratory Argonne, IL 60439
ABSTRACT TiO2 thin films grown on (1120) sapphire at 800 OC by the MOCVD technique have been characterized by transmission electron microscopy. The TiO 2 thin films are single crystalline and have the rutile structure. The epitaxial orientation relationship between the TiO 2 thin films (R) and the substrate (S) has been found to be: (101)[00]RIil 1l02 )[0001Is. Growth twins in the films are commonly observed with the twin plane ( 101 and twinning direction . Detailed atomic structures of the twin boundaries and TiO2/ot-Al 2 0 3 interfaces have been investigated by highresolution electron microscopy (HREM). When the interfaces are viewed in the direction of [0i0]R/[000l]S, the interfaces are found to be structurally coherent in the direction of [iOl]R/[1 i00]s, in which the lattice mismatch at the interfaces is about 0.5%.
INTRODUCTION The study of epitaxial growth of ceramic oxide thin films on various substrates has recently received considerable attention [1-3] since the unique physical properties of the ceramic thin films may be useful in electronic and optical device applications. The metal organic chemical vapor deposition (MOCVD) technique, which has been applied with great success in the semiconductor industry, can also be a potential technique for the epitaxial growth of oxide thin films. However, the use of the MOCVD technique for the fabrication of epitaxial oxide films is still in its infancy. Therefore, atomic-resolution characterization of the interface configuration is very important for understanding the epitaxial growth and the fabrication processes. In the present study, titanium oxide (TiO 2) grown on (1120) sapphire (cc-A1 20 3 ) was chosen as a model system to study the epitaxial growth since the bulk structure and physical properties of TiO,2 are well characterized. In addition, these materials exhibit little interdiffusion and no reaction at the growth temperature used in this study. The present work is part of a larger investigation of the heteroepitaxial growth of ceramic oxide films and the orientation relationship between the oxide films and their substrates [2-3]. The structure of the TiO 2/AI 2 0 3 interfaces and defects in the TiO 2 films were characterized using transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM), and the results of this investigation are presented in this paper.
EXPERIMENTAL TiO 2 thin films were prepared in a cold-wall horizontal low-pressure MOCVD system. Titanium isopropoxide (Ti(OC 3H 7)4 ) was used as metal-organic precursor. The precursor vapor was introduced into the reactor by high-purity nitrogen as carrier gas. The TiO 2 thin films were grown on (1120) A12 0 3 at 800 'C. Other growth parameters have been described in detail elsewhere [2].
Mat. Res. Soc. Symp. Proc. Vol. 209. 01991 Materials Research S
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