Abstract
Pure-phase, single-crystalline epitaxial films of α-Fe 2O 3(0001) and Fe 3O 4(001) have been grown on Al 2O 3(0001) and MgO(001) substrates, respectively, using oxygen-plasma-assisted molecular beam epitaxy. We discuss the growth conditions required to synthesize these phases, as well as the associated characterization by means of reflection high-energy electron diffraction, low-energy electron diffraction, and X-ray photoelectron spectroscopy and diffraction. The selective growth of these phases depends critically on the choice of substrate, the iron and oxygen fluxes, and the substrate temperature. MgO(001) and Al 2O 3(0001) were chosen as substrates for the growth of Fe 3O 4(001) and α-Fe 2O 3(0001), respectively, because of good lattice and crystal symmetry matching. The growth of α-Fe 2O 3 is achieved using a low iron-to-oxygen flux ratio compared with that used to grow Fe 3O 4. Fe 3O 4 must be grown at the relatively low substrate temperature of 250°C on MgO(001) to avoid interface reaction and Mg outdiffusion. The α-Fe 2O 3 film surface is unreconstructed whereas the Fe 3O 4 surface exhibits a (√2 × √2)R45° reconstruction. Application of a simple electron counting rule to the Fe 3O 4(001) surface suggests that the reconstruction is due to an ordered array of tetrahedral Fe vacancies.
Published Version
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