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

Single-crystalline Mn 3 O 4 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/Mn 3 O 4 ) layers form firstly, and then Mn 3 O 4 nanostructures grow above the upper metal oxide layer to form multi-layered structures, MnO/Mn 3 O 4 /Mn 3 O 4 –nanoflakes. The nucleation and growth of Mn 3 O 4 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.