PNNL

Abstract

We have grown epitaxial ?-Fe2O3(1010) 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 90º 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 three-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 [1120]Fe2O3 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 [1120]Fe2O3 [100]TiO2 directions.