Growth and characterization of thin epitaxial Co_3O_4(111) films

摘要

The growth and characterization of epitaxial Co_3O_4(111) films grown by oxygen plasma-assisted molecular beam epitaxy on single crystal α-Al_2O_3(0001) is reported. The Co_3O_4(111) grows single crystalline with the epitaxial relation Co_3O_4(111)[121]‖α-Al_2O_3(0001)[1010], 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 Co_3O_4 films are fully relaxed. Post-growth annealing induces significant modifications in the film morphology, including a sharper Co_3O_4/α-Al_2O_3 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 CO_3O_4(111) films are (1 × 1), which can be explained in terms of a surface inversion in the spinel structure.