Co–Fe Mixed Oxide Nanoneedle-on-Nanowall Arrays on Conductive Substrate: Synthesis and Field Emission

We report the fabrication of Co–Fe mixed oxides with an intriguing hierarchical nanostructure built on Fe–Co–Ni alloy substrate. This novel structure comprises two-dimensional (2D) nanostructured arrays and onedimensional (1D) nanoneedles aligned on their top. The possible growth mechanism has been discussed in details on the basis of time-dependent experiments. The results indicate that the formation of 1D/2D nanostructures results from the secondary growth of Co-based hydroxides on layered double hydroxide (LDH) nanowalls. The precursor materials can be further transformed into Co–Fe mixed oxides by annealing in Argon atmosphere. Then, the nanostructured film of Co–Fe mixed oxides was investigated as cathode for field emission (FE) application. This work presents not only one kind of Co-based mixed oxides for possible FE cathode, but also a tunable pathway to build well-engineered hierarchical nanostructures.