cm-self -assemble of Co hydrooxide.pdfVIP

/cmPublished on Web 11/16/2010r 2010 American Chemical Society Chem. Mater. 2010, 22, 6341–6346 6341 DOI:10.1021/cm1021678 Self-Assembled Nanofilm ofMonodisperse Cobalt Hydroxide Hexagonal Platelets: Topotactic Conversion into Oxide and Resistive Switching Renzhi Ma,* Minoru Osada, Linfeng Hu, and Takayoshi Sasaki International Center for Materials Nanoarchitectonics, National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan Received August 1, 2010. Revised Manuscript Received September 20, 2010 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. Introduction Solution-based self-assembly, as a bottom-up approach that can be carried out under mild conditions, has high technical attractiveness for rational design and construction of nanoarchitectures as device components because of methodological simplicity, low cost, and low environmental impact.1,2 Recently, monolayer films of spherical or poly- hedral nanoparticles with high regularity were achieved by some solution-based techniques, e.g., Langmuir-Blodgett (LB) method2 and oil/water interfacial self-assembly.3,4 In contrast tonanoparticles, platelet crystallites, becauseof their peculiar two-dimensional (2D) anisotropy, may be natu