The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes
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The Crystallography of Metal Halides formed within Single Walled Carbon Nanotubes J. Sloan1,2, G. Brown1,2, S.R. Bailey1, K.S. Coleman1, E. Flahaut1, S. Friedrichs1, C. Xu1, M.L.H. Green1, R.E. Dunin-Borkowski2, J.L. Hutchison2, A.I. Kirkland3 and R.R. Meyer3 1 Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR, U.K. 2 Department of Materials, University of Oxford, Parks Road, Oxford, OX1 3PH, U.K. 3 Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, U.K. ABSTRACT The crystal growth behaviour and crystallography of a variety of metal halides incorporated within single walled carbon nanotubes (SWNTs) as determined by high resolution electron microscopy (HRTEM) is described. Simple packed structures, such as the alkali halides, form related structures within SWNTs that are found to be integral atomic layers in terms of their thickness as a function of the encapsulating SWNT diameter. An enhanced HRTEM image restoration technique reveals precise data concerning lattice distortions present in these crystals. More complex structures, such as those derived from 3D complex, layered and chain halides form related crystal structures within SWNTs. In narrow SWNTs (i.e. with diameters less than ca. 1.6 nm), structures consisting of individual 1D polyhedral chains (1D-PHCs) were obtained that were derived from the corresponding bulk halides structures. In the case of infinite 3D network and layered halides, the 1D polyhedral chains form with lower co-ordinations than in the bulk. Molecular halides also intercalate into SWNTs but these do not readily form organised structures within SWNTs. INTRODUCTION Single walled carbon nanotubes (SWNTs) are the ultimate discrete porous structures, consisting of individual sp2 carbon cylinders with lengths in the µm range and diameters varying from ca. 1 nm up to ca. 4 nm, although the majority (80-90%) exist within a narrow 1.4-1.6 nm range. We have been preparing composites from SWNTs using a capillary method [1,2] with a view to modifying their physical properties. A key aspect of this work involved studying the crystal growth of materials formed inside SWNTs which, in most cases leads to 1D crystal growth behaviour that can be related to the bulk structure of the incorporated halide. We have been studying the crystal growth behaviour of a wide variety of metal halides as a function of bulk structure type (Table 1) and have characterised the crystal growth behaviour within SWNTs, using HRTEM imaging, structural modelling and image simulation. EXPERIMENTAL DETAILS The nanotubes were produced by a high yield arc synthesis method [3] and then filled in 20-70% yield by the capillary wetting technique [1,2]. The samples were examined at 300 kV in a JEOL JEM-3000F HRTEM, which has a low spherical aberration coefficient Cs of 0.6 mm and a point resolution of 0.16 nm. Images were acquired digitally on a Gatan model 794 (1k × 1k) CCD camera, and the magnification was calibrated accurately using Si(110) lattice fringes.
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