Abstract
We have grown epitaxial α-Fe 2O 3(0 0 0 1) thin films on Pt(1 1 1) α- Al 2 O 3(0 0 0 1) , and γ-Fe 2O 3(0 0 1) and Fe 3O 4(0 0 1) thin films on MgO(0 0 1) by molecular beam epitaxy using an elemental Fe source and an electron cyclotron resonance oxygen plasma source. These iron oxide thin films are single crystals with excellent crystalline quality. Use of a Pt(1 1 1) buffer layer for growth of α-Fe 2O 3(0 0 0 1) on α-Al 2O 3(0 0 0 1) improves the crystal quality for epitaxial α-Fe 2O 3(0 0 0 1) films. Growth of epitaxial α-Fe 2O 3 and γ-Fe 2O 3 films under the same growth conditions, but on different substrates, suggests that it is possible to grow a thermodynamically unstable or metastable phase such as γ-Fe 2O 3 by selecting a suitable substrate (e.g. small lattice mismatch and similar surface symmetry). The α-Fe 2O 3(0 0 0 1) and α-Fe 2O 3(0 0 1) film surfaces are unreconstructed whereas the Fe 3O 4(0 0 1) film surface exhibits a (√2 × √2)R45° reconstruction. Application of a simple electron counting rule reveals that the bulk-terminated α-Fe 2O 3(0001) and γ-Fe 2O 3(0 0 1) surfaces are autocompensated, but the bulk-terminated Fe 3O 4(0 0 1) surface is not. The reconstruction is due to the formation of an ordered array of tetrahedral iron vacancies required to achieve surface charge neutralization.
Published Version
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