Epitaxial stabilization of orthorhombic cuprous oxide films on MgO(110)

Continuous epitaxial films of cuprous oxide (Cu₂O) have been formed by the thermal oxidation of 1.5-μm-thick Cu metal films deposited on MgO(110) substrates. These films melted at 1118 °C in air, in agreement with equilibrium phase diagrams. Upon cooling from the liquid, a highly crystalline, epitaxial, 2.5-μm-thick Cu₂O film was formed. X-ray diffraction spectroscopy revealed that the Cu₂O film crystal structure was orthorhombically distorted from the bulk cubic crystal structure. High-resolution transmission electron microscopy showed that the film is coherent, and energy dispersive x-ray spectroscopy showed that interdiffusion is limited to the interface. These results suggest that a new epitaxially stabilized phase of Cu₂O has been formed.