Effect of lattice mismatch on the epitaxy of sol-gel LiNbO3 thin films

A solution precursor method based on metal alkoxides was used to produce epitaxial LiNbO3 thin films, ≈200 nm thick, on (0001) sapphire substrates. Transmission electron microscopy revealed that the major cause of surface roughness in these films was grain boundary grooves between mosaic grains with misorientations ⩽5°. It is postulated that these low angle boundaries directly result in surface grooving and roughness. The epitaxial films also contained two distinguishable variants in the film/substrate interfacial plane, namely, an aligned variant, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left\langle {\overline 1 } \right.2\overline 1 {\left. 0 \right\rangle _{{\rm{LiNb}}{{\rm{O}}_3}}}$\end{document}||\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left\langle {\overline 1 } \right.2\overline 1 {\left. 0 \right\rangle _{{\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3}}}$\end{document} and a 60° rotated variant, \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left\langle {\overline 1 } \right.2\overline 1 {\left. 0 \right\rangle _{{\rm{LiNb}}{{\rm{O}}_3}}}$\end{document} || \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\left\langle 1 \right.\overline 2 1{\left. 0 \right\rangle _{{\rm{LiNb}}{{\rm{O}}_3}}}$\end{document}. A seeded grain growth method was used to minimize the presence of the 60° rotated variant. An epitaxial buffer layer of Fe2O3 was used to lower the mismatch strain, eliminate the 60° rotated variant, and reduce the mosaic nature of the LiNbO3 film. X-ray rocking curve full-width-at-half-maximum (FWHM) values measured on the (0112) film peak indicate that the mosaic character can be reduced from 1.5° to 0.76° by using a buffer layer.