Epitaxial growth of manganese oxide films on MgAl2O4 (001) substrates and the possible mechanism

• Three types of manganese oxide films were grown on MgAl2O4 (001) substrates by molecular beam epitaxy.
• The structural characteristics and chemical compositions of the films were investigated systematically by using multiple measurement methods.
• The critical thicknesses of the films are different under different growth conditions.
• An epitaxial stabilization model was used to explain the growth mechanism of the films.

Three types of manganese oxide films were grown on MgAl2O4 (001) substrates by plasma-assisted molecular beam epitaxy (PA-MBE) under different growth rates and substrate temperatures. The structural characteristics and chemical compositions of the films were investigated by using in-situ reflection high-energy electron diffraction (RHEED), ex-situ X-ray diffraction, Raman, and X-ray photoelectron spectra (XPS). At a lower substrate temperature (730 K), the epitaxial film tends to form mixed phases with a coexistence of Mn3O4 and Mn5O8 in order to relieve the mismatch-strain. However, at a higher substrate temperature (750 K), all of the films crystallize into Mn3O4; the critical thickness of the film grown under a lower growth rate (7 Å/min) is much larger than that under a high growth rate (10 Å/min). When the film reaches a certain critical thickness, the surface will become fairly rough, and another oriented phase Mn3O4 would crystallize on such a surface.