Microstructure of epitaxial potassium niobate thin films prepared by metalorganic chemical vapor deposition

Abstract

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.

Hydrothermal epitaxy of KNbO3 thin films and nanostructures

“…Unfortunately, it is very difficult to grow bulk KNbO 3 crystals and as such, much attention has been paid to growing epitaxial KNbO 3 films. Existing methods for producing heteroepitaxial KNbO 3 thin films include pulsed laser deposition, metal-organic chemical vapor deposition, ion beam sputtering and sol-gel processing [7][8][9][10]. All of these methods require processing temperatures above 700 1C.…”

Thermodynamic theory of epitaxial ferroelectric thin films with dense domain structures

“…The twinning of epitaxial layers was predicted theoretically by Roitburd already in 1976, 1 and during the past decade domain patterns were found in PbTiO 3 , Pb(Zr x Ti 1-x )O 3 , (Pb 1-x La x )TiO 3 , BaTiO 3 , KNbO 3 , and SrBi 2 Ta 2 O 9 films grown on various singlecrystalline substrates. [2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] The experimental observations triggered intensive theoretical studies of the statics and dynamics of elastic domains (twins) in epitaxial ferroelectric and ferroelastic thin films. 1,[21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37] In the general case, the problem is very complicated because of substantial inhomogeneity of internal mechanical stresses in polydomain (twinned) films.…”

Effect of finite domain-wall width on the domain structures of epitaxial ferroelectric and ferroelastic thin films

“…The self-energy W s of the dislocation ensemble also may be found by the direct integration of the relevant stresses T 11 and T 22 , being the sum of the inhomogeneous component ͑10͒ and an additional uniform field discussed in Sec. II.…”

“…Polydomain states have been observed in PbTiO 3 , Pb(Zr x Ti 1Ϫx )O 3 , (Pb 1Ϫx La x )TiO 3 , KNbO 3 , and YBa 2 Cu 3 O 7 thin films grown on various substrates. [1][2][3][4][5][6][7][8][9][10][11][12][13] Important data have been obtained showing that the formation of multiple domain patterns may influence significantly the physical properties of ferroelectric films. It was found, for instance, that the relative population of ferroelastic domains in the film has a strong impact on the polarization hysteresis loops exhibited by ferroelectric layers.…”