1D P-Block Halide Crystals Confined into Single Walled Carbon Nanotubes
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1D P-Block Halide Crystals Confined into Single Walled Carbon Nanotubes E. Flahaut1, J. Sloan1,2, K.S. Coleman1, V.C. Williams1, S. Friedrichs1, N. Hanson1 and M.L.H. Green1 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. ABSTRACT The synthesis and characterisation of one-dimensional (1D) crystals that have a wellspecified chemistry, size and crystal structure have presented a formidable challenge for materials chemistry and analysis. We report here the filling of single (SWNTs) and double walled carbon nanotubes (DWNTs) by two different p-block halides, TlCl and PbI2. The nanotubes were produced either by the arc synthesis [1] or by a CVD method [2], based on the reduction of a Mg0.9Co0.1O solid solution by a hydrogen-methane mixture. In the case of TlCl, the structure of the crystals observed inside the tubes were all found to be derived from the rocksalt form and bilayer crystals were observed which exhibited reduced coordination relative to the fcc structure, as determined from high resolution transmission electron microscopy (HRTEM). In contrast, the crystal structure of bulk TlCl is a CsCl type structure. These results are consistent with the recently reported reduced coordination KI crystals formed within SWNTs [3]. In the case of PbI2 (i.e. with the CdCl2 structure), the use of HRTEM images combined with image simulations was used to confirm the partially reduced coordination of Pb atoms within the SWNT and DWNT confined 1D crystals. INTRODUCTION Metal halides may be introduced into SWNTs by capillarity [1, 4]. These experiments permit the study of low dimensional crystal growth whereby the incorporated material is constrained by the encapsulating van der Waals surface of the carbon capillaries, to a few atomic layers in thickness. The preparation of highly anisotropic 1D structures confined into SWNTs is one of the key objectives in carbon research, as the introduction of these materials into the hollow nanotubes cavities could result in interesting effects on their physical and electronic properties. EXPERIMENTAL DETAILS The nanotubes were produced either by arc synthesis or by a CVD method based on the reduction of a Mg0.9Co0.1O solid solution by a H2-CH4 mixture. In this latter case, concentrated HCl (12M) was used to remove most of the catalyst [2]. The nanotubes were filled in high yield by the capillary wetting technique [1, 4]. The samples were examined at 300 kV in a JEOL JEM3000F HRTEM, which has a low spherical aberration coefficient Cs of 0.6mm and a point resolution of between 0.16-0.17nm. Images were acquired digitally on a Gatan model 794 (1k × 1k) CCD camera, and the magnification was calibrated accurately using Si lattice
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fringes. Energy dispersive X-ray microanalysis (EDX) was performed with a LINK ‘ISIS’ system using a 0.5nm diameter electron probe. RESULTS AND DISCUSSION TlCl, which can crystallize both with the Pm3m CsCl-type structure and with th
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