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      Kinetically Controlled Fabrication of Single‐Crystalline TiO 2 Nanobrush Architectures with High Energy {001} Facets

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          Abstract

          This study demonstrates that precise control of nonequilibrium growth conditions during pulsed laser deposition (PLD) can be exploited to produce single‐crystalline anatase TiO 2 nanobrush architectures with large surface areas terminated with high energy {001} facets. The data indicate that the key to nanobrush formation is controlling the atomic surface transport processes to balance defect aggregation and surface‐smoothing processes. High‐resolution scanning transmission electron microscopy data reveal that defect‐mediated aggregation is the key to TiO 2 nanobrush formation. The large concentration of defects present at the intersection of domain boundaries promotes aggregation of PLD growth species, resulting in the growth of the single‐crystalline nanobrush architecture. This study proposes a model for the relationship between defect creation and growth mode in nonequilibrium environments, which enables application of this growth method to novel nanostructure design in a broad range of materials.

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          Most cited references44

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          Growth of oriented single-crystalline rutile TiO(2) nanorods on transparent conducting substrates for dye-sensitized solar cells.

          Dye-sensitized solar cells (DSSCs) made from oriented, one-dimensional semiconductor nanostructures such as nanorods, nanowires, and nanotubes are receiving attention because direct connection of the point of photogeneration with the collection electrode using such structures may improve the cell performance. Specifically, oriented single-crystalline TiO(2) nanorods or nanowires on a transparent conductive substrate would be most desirable, but achieving these structures has been limited by the availability of synthetic techniques. In this study, a facile, hydrothermal method was developed for the first time to grow oriented, single-crystalline rutile TiO(2) nanorod films on transparent conductive fluorine-doped tin oxide (FTO) substrates. The diameter, length, and density of the nanorods could be varied by changing the growth parameters, such as growth time, growth temperature, initial reactant concentration, acidity, and additives. The epitaxial relation between the FTO substrate and rutile TiO(2) with a small lattice mismatch plays a key role in driving the nucleation and growth of the rutile TiO(2) nanorods on FTO. With TiCl(4)-treatment, a light-to-electricity conversion efficiency of 3% could be achieved by using 4 mum-long TiO(2) nanorod films as the photoanode in a DSSC.
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            Vertically aligned single crystal TiO2 nanowire arrays grown directly on transparent conducting oxide coated glass: synthesis details and applications.

            Single-crystal one-dimensional (1D) semiconductor architectures are important in materials-based applications requiring a large surface area, morphological control, and superior charge transport. Titania has widespread utility in applications including photocatalysis, photochromism, photovoltaics, and gas sensors. While considerable efforts have focused on the preparation of 1D TiO2, no methods have been available to grow crystalline nanowire arrays directly onto transparent conducting oxide (TCO) substrates, greatly limiting the performance of TiO2 photoelectrochemical devices. Herein, we present a straightforward low temperature method to prepare single crystal rutile TiO2 nanowire arrays up to 5 microm long on TCO glass via a non-polar solvent/hydrophilic substrate interfacial reaction under mild hydrothermal conditions. The as-prepared densely packed nanowires grow vertically oriented from the TCO glass substrate along the (110) crystal plane with a preferred (001) orientation. In a dye sensitized solar cell, N719 dye, using TiO2 nanowire arrays 2-3 microm long we achieve an AM 1.5 photoconversion efficiency of 5.02%.
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              Strong polarization enhancement in asymmetric three-component ferroelectric superlattices.

              Theoretical predictions--motivated by recent advances in epitaxial engineering--indicate a wealth of complex behaviour arising in superlattices of perovskite-type metal oxides. These include the enhancement of polarization by strain and the possibility of asymmetric properties in three-component superlattices. Here we fabricate superlattices consisting of barium titanate (BaTiO3), strontium titanate (SrTiO3) and calcium titanate (CaTiO3) with atomic-scale control by high-pressure pulsed laser deposition on conducting, atomically flat strontium ruthenate (SrRuO3) layers. The strain in BaTiO3 layers is fully maintained as long as the BaTiO3 thickness does not exceed the combined thicknesses of the CaTiO3 and SrTiO3 layers. By preserving full strain and combining heterointerfacial couplings, we find an overall 50% enhancement of the superlattice global polarization with respect to similarly grown pure BaTiO3, despite the fact that half the layers in the superlattice are nominally non-ferroelectric. We further show that even superlattices containing only single-unit-cell layers of BaTiO3 in a paraelectric matrix remain ferroelectric. Our data reveal that the specific interface structure and local asymmetries play an unexpected role in the polarization enhancement.
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                Author and article information

                Contributors
                hnlee@ornl.gov
                Journal
                Adv Sci (Weinh)
                Adv Sci (Weinh)
                10.1002/(ISSN)2198-3844
                ADVS
                Advanced Science
                John Wiley and Sons Inc. (Hoboken )
                2198-3844
                05 April 2017
                August 2017
                : 4
                : 8 ( doiID: 10.1002/advs.v4.8 )
                : 1700045
                Affiliations
                [ 1 ] Oak Ridge National Laboratory Oak Ridge TN 37831 USA
                Author notes
                [*] [* ]E‐mail: hnlee@ 123456ornl.gov
                Article
                ADVS313
                10.1002/advs.201700045
                5566339
                4efeb6c9-d8fa-4f75-9a85-217a82b991d3
                © 2017 The Authors. Published by WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 30 January 2017
                : 14 February 2017
                Page count
                Figures: 5, Tables: 0, Pages: 6, Words: 4543
                Funding
                Funded by: U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division
                Categories
                Full Paper
                Full Papers
                Custom metadata
                2.0
                advs313
                August 2017
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.1.7 mode:remove_FC converted:22.08.2017

                defect‐mediated aggregation,high energy {001} facets,kinetic growth control,pulsed laser deposition,tio2 nanostructures

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