Formation of Three-Dimensional Urchin-like α-Fe2O3 Structure and Its Field-Emission Application

A three-dimensional urchin-like alpha-Fe2O3 microstructure is formed via a simple, template-free, and one-step thermal oxidation of Fe spheres in an air atmosphere at temperatures in the range of 300-450 degrees C. The urchin-like alpha-Fe2O3 microstructure consists of crystalline alpha-Fe2O3 nanoflakes grown perpendicularly on the surface of the sphere, a shell layer of alpha-Fe2O3/Fe3O4, and an Fe core. During the oxidation process, the nanoflakes germinate and grow from cracks in the oxidation layer on the surface. The length of the nanoflakes increases with oxidation time. The tip diameters of the nanoflakes are in ranges of 10-20 nm at 300 degrees C, 20-30 nm at 350 degrees C, and 40-60 nm at 400 degrees C; the length can reach up to a few micrometers. The field-emission characteristics of the samples are experimentally studied and simulated. The results show that the urchin-like emitter has a low turn-on field of 2.8 V/mu m, high field-enhancement factor of 4313, excellent emission uniformity of over 4 cm(2), and good emission stability during a 24 h test.