Self-Assembled Nanofilm of Monodisperse Cobalt Hydroxide Hexagonal Platelets: Topotactic Conversion into Oxide and Resistive Switching

The current work develops a solution-based self-assembling route to construct close-packed nanofilms (thickness ≈ 30 nm) using monodisperse hexagonal platelets of Co(OH)₂ as two-dimensional building blocks. The hydroxide film was postannealed and could be transformed into [111]-oriented cobalt monoxide (CoO) in a topotactic fashion retaining the original hexagonal platelet shape. Electrical resistive switching property of as-transformed CoO film was investigated, revealing a gigantic change in electrical resistance (ON/OFF current ratio: 10³) and fast switching speed (ns level). This solution-based self-assembly procedure, in combination with a topotactic conversion from lamellar hydroxides to corresponding oxides, offers a new alternative to high-performance thin film devices based on transition metal oxide.