Heteroepitaxial growth and structural analysis of epitaxial α-Fe₂O₃$(10\overline{1}0)$ on TiO₂(001)

Abstract

We grew epitaxial α–Fe₂O₃$(10\overline{1}0)$ on TiO₂(001) rutile by oxygen plasma-assisted molecular-beam epitaxy. High-resolution transmission electron microscopy (HRTEM), reflection high-energy electron diffraction (RHEED), and x-ray diffraction pole figures confirm that the film is composed of four different in-plane orientations rotated by 90° relative to one another. For a given Fe₂O₃ unit cell, the lattice mismatch along the parallel [0001]Fe₂O₃ and [100]TiO₂ directions is nominally +67%. However, due to a 3-fold repetition of the slightly distorted square symmetry of anion positions within the Fe₂O₃ unit cell, there is a coincidental anion alignment along the [0001]Fe₂O₃ and [100]TiO₂ directions, which results in an effective lattice mismatch of only −0.02% along this direction. The lattice mismatch is nearly 10% in the orthogonal $(11\overline{2}0)_{Fe_{2}{O_{3}}}$ and [100]TiO₂ directions. The film is highly ordered and well registered to the substrate despite a large lattice mismatch in one direction. The film grows in registry with the substrate along the parallel [0001]Fe₂O₃ and [100]TiO₂ directions and nucleates dislocations along the orthogonal $(11\overline{2}0)_{Fe_{2}{O_{3}}}$ [100]TiO₂ directions.