title: Nanotubes from Oxide-Based Misfit Family: The Case of Calcium Cobalt Oxide.
abstract: Misfit layered compounds (MLCs) have generated significant interest in recent years as potential thermoelectric materials. MLC nanotubes could reveal behavior that is entirely different from the bulk material. Recently, new chemical strategies were exploited for the synthesis of nanotubular forms of chalcogenide-based MLCs, which are promising candidates for thermoelectric materials. However, analogous synthesis of oxide-based MLC nanotubes has not been demonstrated until now. Here, we report a chemical strategy for synthesis of cobalt-oxide-based misfit nanotubes. A combination of high-resolution (scanning) transmission electron microscopy (including image simulations), spatially resolved electron energy-loss spectroscopy, electron diffraction, and density functional theory (DFT) calculations is used to discover the formation of a phase within these nanotubes that differs significantly from bulk calcium cobaltite MLCs. Furthermore, DFT calculations show that this phase is semiconducting with a band gap in excess of 1 eV, unlike bulk calcium cobaltite MLCs, which are known to be metallic. Through systematic experiments, we propose a formation mechanism for these nanotubes that could also apply more generally to realizing other oxide-based MLC nanotubes.
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , 76100 Rehovot, Israel.
authors.forename: Leela S
authors.initials: LS
authors.lastname: Panchakarla
authors.affiliation: Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón, Universidad de Zaragoza , 50018 Zaragoza, Spain.
authors.forename: Luc
authors.initials: L
authors.lastname: Lajaunie
authors.affiliation: Department of Mechanical and Industrial Engineering, University of Massachusetts Amherst , Amherst, Massachusetts 01003, United States.
authors.forename: Ashwin
authors.initials: A
authors.lastname: Ramasubramaniam
authors.affiliation: Laboratorio de Microscopías Avanzadas, Instituto de Nanociencia de Aragón, Universidad de Zaragoza , 50018 Zaragoza, Spain.|ARAID Foundation , 50018 Zaragoza, Spain.
authors.forename: Raul
authors.initials: R
authors.lastname: Arenal
authors.affiliation: Department of Materials and Interfaces, Weizmann Institute of Science , 76100 Rehovot, Israel.
authors.forename: Reshef
authors.initials: R
authors.lastname: Tenne
keywords: DFT; EELS-STEM; nanotubes; oxide-based misfit layered compounds (MLCs)