Shells, Fibers, and Superstructures

The growth of nanometer-sized crystalline materials with orientational and morphological control is essential for certain applications. However, even when this can be achieved, the preparation techniques required are usually complex and specific to a single system. The discovery of size, shape, and array controls of TiO2 nanomaterials via heteroepitaxy offers a much simpler way to produce complex nanomaterials.

Steven L. Suib et al. from the University of Connecticut have now demonstrated an inexpensive and scaleable hydrothermal route to produce heteroepitaxial rutile TiO2 nanoscale shell–fiber superstructures (NSFS) on cryptomelane MnO2 substrates. The mechanism study shows that the nanoshell is formed prior to the surface nanofibers. The whole growth process is highly dependent on the interface misfits of materials.

When this procedure is applied to thin-film cryptomelane MnO2 substrates, the result is uniform TiO2 nanofiber arrays over large areas, indicating the potential of this approach for use in sensors and energy-harvesting devices.The cryptomelane MnO2 substrate can also be chemically removed from the superstructures to give hollow nanostructures. The successful extension of this work to the production of epitaxial rutile SnO2 NSFS may be the basis for a much more general approach for the growth of metal oxide nanostructures. Electron microscopy images of the shell/fiber superstructures can be seen on the cover of issue 9 of Small.

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