One-step thermal oxidation synthesis of large-area Mn3O4 nanoflakes at low temperature in air atmosphere

Single-crystalline Mn3O4 nanoflakes were grown on manganese sheets by one-step thermal oxidation process at 360–500 °C in ambient atmosphere. The samples were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD), Raman and transmission electron microscope (TEM). The nanoflakes with a size of 15–20 nm in thickness, ~60 nm in width, and ~210 nm in length are obtained at 360 °C for 24 h. A surface diffusion mechanism is proposed to explain the growth of manganese oxide nanostructures via thermal oxidation, which includes two steps: manganese oxide (MnO/Mn3O4) layers form firstly, and then Mn3O4 nanostructures grow above the upper metal oxide layer to form multi-layered structures, MnO/Mn3O4/Mn3O4–nanoflakes. The nucleation and growth of Mn3O4 nanostructures are related to the surface energy and different growth rates along different crystal directions, which are controlled by the diffusion of the metal and gas molecule.