Directional etching formation of single-crystalline branched nanostructures: A case of six-horn-like manganese oxide

In this paper, we successfully synthesized six-horn-like branched MnO nanocrystals by thermal decomposition of Mn(CH3CO2)2 ̇4H2O in the present of 1-octylamine/oleic acid (OA) at 400 °C for 30 min. SEM and TEM observation indicate that every horn of six-horn-like MnO nanocrystals is constructed with a bundle of nanorods growing along the [100] direction. Adequate evidence provided by time- and temperature-dependent experiments demonstrates that the formation of such branched MnO can be divided into two processes, i.e., the formation of octahedron-based MnO exposed with polar surfaces and sequent directional etching. In this mechanism, the mixed solvent of organic amines and OA provides favorable circumstances for the formation of MnO octahedra, and at the same time, OA as the etching reagent is responsible for the evolution of six-horn-like MnO from octahedron-based MnO.