Structural and Morphological Variations of Encapsulated Metal Oxides in Single Walled Carbon Nanotubes
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Structural and Morphological Variations of Encapsulated Metal Oxides in Single Walled Carbon Nanotubes Pedro M.F.J. Costa1,*, Narun Thamavaranukup1, Thomas Rutherford1, Steffi Friedrichs1, Jeremy Sloan1,2, Malcolm L. H. Green1 1
Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, OX1 3QR, UK Department of Materials Science, University of Oxford, Parks Road, Oxford, OX1 3PH, UK *Now at Department of Materials Science and Metallurgy, University of Cambridge, Pembroke Street, Cambridge, CB2 3QZ, UK 2
Abstract Single walled carbon nanotubes have been filled with a variety of metal oxides and the structural and morphological characteristics of the metal_oxide@SWNT composites studied. Advanced techniques of software aberrations correction for transmission electron microscopy were used for characterisation. This research shows that, despite their higher reactivity compared to salts such as halides, oxides can be encapsulated within SWNTs with some compounds attaining remarkable filling yields.
Introduction Since the groundbreaking report by Ajayan et al. in 1993 [1], the study of materials encapsulation in carbon nanotubes has seen a remarkable development. The main drive behind the interest of filled carbon nanotubes lies in the potential to change (and possibly tailor) the mechanical, magnetic, electronic and optical properties of the nanotube and/or encapsulated materials [2,3]. Despite the considerably body of work, few reports are known of metal oxides filled single walled carbon nanotubes (SWNTs) [4,5]. This is explained mainly by the wide range of physical properties that oxides present (melting points, surface tensions, etc.) and the fact that they are much more chemically reactive than, for instance, metal halides. This reactivity may effectively lead to partial or complete oxidation of the carbon lattice in particular when filling strategies such as the high temperature capillary procedure are used. Nonetheless, due to the technological and scientific importance of this class of materials, exploring the possibility of encapsulating oxides within SWNTs should not be disregarded. We have therefore established a research programme that has covered several different metal oxides, from 3d to 5d transition metals. It is particularly interesting that a variety of morphologies (from clusters to nanowires), filling yields and structural behaviours can be found for the metal_oxides@SWNT composites studied, some of which are briefly described here.
Experimental details The SWNTs used in this work were produced using an automated arc-evaporation machine. The carbon rods (acting as anodes) were 50 mm in length with an external diameter of 6 mm. A 4.5 mm hole was drilled and later packed, in a dry box, with a catalyst powder consisting of high-purity dried graphite powder and 1 at% Y / 4.2 at% Ni [6]. A Schlenk tube was used to transport the filled rod to the arc reactor. Helium gas, set at a pressure of ca.600 mbar and flowing at 500 ml/min was used in addition to an arc
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