Encapsulated Molecules in Carbon Nanotubes: Structure and Properties
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Encapsulated Molecules in Carbon Nanotubes: Structure and Properties Richard Russo, Brian W. Smith, B.C. Satishkumar, David E. Luzzi* Laboratory for Research in the Structure of Matter *Department of Materials Science and Engineering University of Pennsylvania 3231 Walnut Street, Philadelphia, PA 19104-6272, USA Harry C. Dorn Department of Chemistry Virginia Polytechnic Institute and State University Blacksburg, Virginia 24061, USA
ABSTRACT We encapsulate a number of fullerenes inside single-walled carbon nanotubes (SWNTs) including La2@C80 and ErxSc3-xN@C80(x=0-3). The structural properties of these nanoscopic hybrid materials are described using high resolution transmission electron microscopy and electron diffraction. It is found that the encapsulated fullerenes selfassemble into long, one-dimensional chains. The thermal stability of these supramolecular assemblies are studied and large variations are found. The behavior is nominally consistent with the mass of the encapsulated metallofullerenes. INTRODUCTION Many future applications of single-walled carbon nanotubes (SWNTs) will depend upon the ability to modify their intrinsic properties by manipulating their structure. One novel means for modifying the properties of a SWNT is through the filling of its interior cavity with other molecules. For example, we have shown that “peapods,” comprising SWNTs filled with 1-D chains of C60, can be manufactured via a vapor phase and/or surface diffusion mechanism. This scalable process consists of annealing the sample in the presence of C60 at ~400°C. The presence of interior C60 is known to decrease the SWNT’s compressibility [1] and has been shown by molecular dynamics simulation to increase its elastic modulus [2]. Our method of encapsulation has recently been extended to other related molecules, including the metallofullerenes La2@C80 and Gd@C82. The case of La2@C80@SWNT served as the first definitive proof that a non-intrinsic molecule could be inserted in bulk into SWNTs. In these experiments, it was directly observed by transmission electron microscopy (TEM) that the La atoms within the encapsulated C80 cages tumbled in a discontinuous motion [3], in direct conflict with the continuous motion detected by solution NMR experiments [4]. This was interpreted as the result of an interaction W1.3.1
between the SWNT and the contained La2@C80 molecules, providing yet another indication that interior molecules can modify the properties of a SWNT. In the case of Gd@C82@SWNT, preliminary results indicate that the electrical resistance of a SWNT mat was affected by the presence of interior Gd@C82 [5]. The present work involves a novel endohedral metallofullerene system, ErxSc3N@C x 80 (x =0-3). This system comes with the ability to substitute several different metals in the nitrogen cluster, which will undoubtedly affect the charge transfer properties between the metal nitride cluster and the fullerene cage. These effects, when coupled with encapsulation in SWNTs, will create a series of hybrid materials with tunable electro
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