Transmission electron microscopy and electron energy-loss spectroscopy analysis of manganese oxide nanowires

Abstract

Single-crystalline MnOOH and ${\mathrm{Mn}}_3{\mathrm{O}}_4$ nanowires have been prepared by hydrothermal treatment of commercial bulky manganese oxide particles. $\beta \text{-}{\mathrm{MnO}}_2$ and $\alpha \text{-}{\mathrm{Mn}}_2{\mathrm{O}}_3$ nanowires were prepared by calcination of MnOOH nanowires. Transmission electron microscopy analysis demonstrates that MnOOH nanowires grow directly from ${\mathrm{MnO}}_2$ raw particles. The diameter of the nanowires is 20–70 nm, while the length can reach several micrometers. MnOOH nanowires grow preferentially along the [010] direction and ${\mathrm{Mn}}_3{\mathrm{O}}_4$ nanowires prefer to grow along the [001] direction; the long dimension of both $\beta \text{-}{\mathrm{MnO}}_2$ and $\alpha \text{-}{\mathrm{Mn}}_2{\mathrm{O}}_3$ nanowires is along [001]. Electron energy-loss spectroscopy analysis shows that the position of the prepeak of the oxygen $K$ edge shifts to higher energy and the energy separation between the two main peaks of the oxygen $K$ edge decreases with decreasing manganese oxidation state. The manganese-white-line ratios $(L_3∕L_2)$ were calculated.