Heteroepitaxial growth and structural analysis of epitaxial alpha=Fe_2O_3(1010) on TiO_2(001)

摘要

We grew epitaxial alpha-Fe_2O_3(1010) on TiO_2(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 deg relative to one another. For a given Fe_2O_3 unit cell, the lattice mismatch along the parallel [0001]_(Fe_2o_3) and [100]_(TiO_2) directions is nominally +67 percent. However, due to a 3-fold repetition of the slightly distorted square symmetry of anion positions within the Fe_2O_3 unit cell, there is a coincidental anion alignment along the [0001]_(Fe_2o_3) and [100]_(TiO_2) directions, which results in an effective lattice mismatch of only-0.02 percent along this direction. The lattice mismatch is nearly 10 percent in the orthogonal [V120]_(Fe_2o_3) and [100]_(TiO_2) 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]_(Fe_2o_3) and [100]_(Tio_2) directions and nucleates dislocations along the orthogonal [1120]_(Fe_2o_3) [100]_(TiO_2) directions.