Adding metal to carbon: Production and properties of metallofullerenes and single-layer nanotubes

Metal atoms can be trapped inside fullerene cages as they form from condensing carbon vapor. In favorable cases, such as with lanthanides, roughly a few percent of the fullerenes extracted from the soot produced by co-vaporizing metal with the carbon will contain one or more metal atoms. Pure samples of such metallofullerenes have been obtained using HPLC, allowing detailed characterization of these novel molecules. Structural studies have been carried out using transmission electron microscopy (TEM), scanning electron microscopy (STM), X-ray absorption fine structure (XAFS), X-ray diffraction (XRD) and electron spin resonance spectroscopy (ESR). ESR in particular has been used to address the interesting question of whether the internal atoms can move with respect to the fullerene cage. On the other hand, adding transition metals such as cobalt to the carbon vapor leads to the production of nanometer-diameter, single-layer carbon nanotubes with lengths up to micrometers, rather than metallofullerenes.