Growth and characterization of thin epitaxial Co3O4(111) films

The growth and characterization of epitaxial Co3O4(111) films grown by oxygen plasma-assisted molecular beam epitaxy on single crystal α-Al2O3(0001) is reported. The Co3O4(111) grows single crystalline with the epitaxial relation Co3O4(111)[1¯21¯]‖α-Al2O3(0001)[101¯0], as determined from in situ electron diffraction. Film stoichiometry is confirmed by X-ray photoelectron spectroscopy, while ex situ X-ray diffraction measurements show that the Co3O4 films are fully relaxed. Post-growth annealing induces significant modifications in the film morphology, including a sharper Co3O4/α-Al2O3 interface and improved surface crystallinity, as shown by X-ray reflectometry, atomic force microscopy and electron diffraction measurements. Despite being polar, the surface of both as-grown and annealed Co3O4(111) films are (1×1), which can be explained in terms of a surface inversion in the spinel structure.