Growth of Nano-Needles of Manganese(IV) Oxide by Atomic Layer Deposition

Needles of manganese(IV) oxide in the nanometer range have been synthesised using the atomic layer deposition technique. Traditionally the atomic layer deposition technique is used for the fabrication of thin films, however, we find that needles of β-MnO2 are formed when manganese(IV) oxide is deposited as relatively thick (ca. 800 nm) thin films on substrates of α-Al2O3 [(001) and (012) oriented]. There is no formation of needles when the film is deposited on substrates such as Si(100) or soda lime glass. The film is formed using Mn(thd)3 (Hthd = 2,2,6,6-tetramethylheptane-3,5-dione) and ozone as precursors. While thin films (ca. 100 nm) consist of ε′-MnO2,22, 23 the same process applied to thicker films results in the formation of nano-needles of β-MnO2. These needles of β-MnO2 have dimensions ranging from approximately 1.5 μm at the base down to very sharp tips. The nano-needles and the bulk of the films have been analysed by atomic force microscopy, scanning electron microscopy, X-ray diffraction, and transmission electron microscopy.