Heteroepitaxy of cubic zirconia on basal and prismatic planes of sapphire
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The epitaxial growth of yttria stabilized cubic zirconia produced via the solution precursor route deposited onto the basal and prismatic planes of sapphire was characterized. The evolution of the polycrystalline thin film was described with reference to two concurrent physical processes: abnormal grain growth due to the growth of grains with preferred orientations and a morphological instability which resulted in an uncovering of the substrate. X-ray diffraction, electron backscattering patterns (EBSP), and transmission electron microscopy (TEM) (plan- and cross-sectional view) were used to determine the epitaxial relation (normal and in-plane). The observed epitaxial orientations for the two substrate planes are listed in Table I. A computer search was used to determine the planar, near coincident site lattices (NCSL) for the observed normal epitaxial relations (c-plane: [001]Zro2||[0001]Ai2o3; a-plane: [001]Zro2ll[T2T0]Ai2o3). The determined NCSL's did include all the observed epitaxial relations, but also included others not observed within the same range of misfit and coincident site density.
I. INTRODUCTION The technological importance of inorganic, singlecrystal thin films, patterned for devices that utilize properties such as electro-optical, ferroelectrical, and superconductivity is well recognized. The solution precursor method for thin film epitaxy is of interest because multielement compositions can be precisely mixed as solutions and the method, substrate coating and thin film epitaxy via heat treatment, requires little capital investment. As reviewed elsewhere,1-2 a variety of different solution precursors, most based on metal-organic chemistries, are available for thin film epitaxy. Gel-forming precursors prevent elements, mixed in solution at the molecular scale, from partitioning prior to crystallization. Substrate coating is accomplished by either spinning or dipping; excess solvent evaporates during coating. Precursor films decompose to the desired inorganic compound during heating. Crystallization occurs either during or subsequent to decomposition. The initial inorganic film is not fully dense until heated to higher temperatures due to the evolution of volatile components during decomposition. Thus, prior to the epitaxial phenomena, the inorganic films can be either a glass with nanometer pores or polycrystalline with nanometer grains and pores. The epitaxy phenomena associated with the solution precursor method3 will be different from phenomena known for vapor phase epitaxy.4
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Present address: Centre for Advanced Materials Technology, University of Warwick, Coventry, CV4 7AL, United Kingdom.
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http://journals.cambridge.org
J. Mater. Res., Vol. 9, No. 3, Mar 1994
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Three different solid-state epitaxy mechanisms have been identified.3 One involves the consumption of other polycrystalline grains by grains at the film/substrate interface that crystallize during decomposition with the same orientation as the substrate. This mechanism, known to occur when the struct
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