The microstructure of (001)p-oriented (subscript p indicates the choice of a pseudocubic unit cell) potassium niobate (KNbO3) thin films grown by metalorganic chemical vapor deposition on (100)p lanthanum aluminate and having a large second-order nonlinear optical response is examined. Transmission electron microscopy reveals the films to be epitaxial and the film/substrate interface to be abrupt and semicoherent. The strain between the film and substrate due to the 5% lattice constant mismatch is accommodated by formation of an array of misfit dislocations as well as 60° and 120° ferroelectric microdomains. The domains are located in a 20 nm thick region adjacent to the interface. Beyond the multidomain region, the film is free of significant defects.
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Nystrom et al. (1996) studied this question.