Growth structure of yttria-stabilized-zirconia films during off-normal ion-beam-assisted deposition
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Growth structure of yttria-stabilized-zirconia films during off-normal ion-beam-assisted deposition Y. Iijima,a) M. Hosaka, N. Tanabe, N. Sadakata, T. Saitoh, and O. Kohno Materials Research Lab., Fujikura Ltd., 1-5-1, Kiba, Koto-ku, Tokyo 135, Japan
K. Takeda Super-GM, 5-14-10, Nishitenma, Osaka 530, Japan (Received 29 May 1997; accepted 22 April 1998)
Biaxially aligned YSZ thin films with strong [100] fiber texture were formed on a polycrystalline Ni-based alloy by off-normal ion-beam-assisted deposition. Growth structures were characterized by x-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy (AFM), etc., and the alignment mechanism was discussed using a selective growth model. Peculiar structural evolution of the crystalline orientation was observed and its development was well described by an exponential equation. It was explained as a collaboration of an anisotropic growth condition and epitaxial crystallization. The [100] fiber texture was formed by columnar structures of diameter of 30 –100 nm, which were composed of 5–10 nm diameter crystallites. Very smooth surfaces were observed by AFM imaging with a roughness of 2–3 nm and a peculiar ripple structure. The origin of the azimuthal alignment was discussed with emphasis on the surface structure of YSZ films produced using ion-beam-assisted deposition (IBAD) and the etching rate measurements of (100) surfaces of YSZ single crystals.
I. INTRODUCTION
On polycrystalline or amorphous substrates, vapordeposited polycrystalline films often have a crystallographic axis of all grains oriented normal to the substrate (fiber texture), but usually azimuthal axes are randomly distributed (uniaxially aligned structure). There have been only a few attempts to control not only the polar axis, but also the azimuthal axes orientation of such films (biaxially aligned structure). Graphoepitaxial methods used in semiconductor technologies are one example.1 “Biaxially aligned structure” is the only known way to eliminate weakly coupled, high-angle grain boundaries and derive full performance of Y–Ba–Cu– O superconducting films.2 Ion-beam-assisted deposition (IBAD) was the first method demonstrated to be capable of producing biaxially aligned films on practical polycrystalline substrates.9 –12 IBAD is a method characterized by an assisting ion beam concurrently bombarding films during growth as shown in Fig. 1. The direction, energy, and mass of bombarding ions are precisely controllable by using ion sources.3 When the incident beam axis is tilted from the substrate normal, assisting ions should have a planar component of momentum, which could impart azimuthal anisotropy to the growing films. In 1985, Yu et al. first demonstrated Nb thin films biaxially aligned a)
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http://journals.cambridge.org
J. Mater. Res., Vol. 13, No. 11, Nov 1998
Downloaded: 16 Mar 2015
on fused silica, with [110] fiber texture and azimuthal o
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