Communications
ADVANCED hl ATE R I A LSbottom edge of the catalyst particle, leading directly to a nested cylindrical structure. This is quite different from the usual metal-catalyzed VGCF[36 -401 and metal catalyzed carbon nanotubes. [2'-241 The relationship between various crystals and the tip structures of the carbon nanotubes they catalyze is now being considered in detail.
ExperimentalPitch carbon was obtained by the thermal decomposition of 3,4,9,10perylenetetracarboxylic dianhydride at 800 "C under a nitrogen atmosphere Hafnium dioxide (99.9% purity) was mixed with the pitch carbon in a weight ratio of 1 :4, and the mixture was thermally annealed at 900°C under vacuum. This produced hafnium carbide, a dark gray solid with a fine crystalline texture. After cooling, the mixture was pressed into a 7 mm hole drilled into a tubular graphite rod 10 mm in diameter (99.99 % purity). During the course of electrlc arc vaporization of the hafnium-composite graphite electrode, the inner pressure of a water-cooled chamber was maintained at 200 Torr and a DC current of 100 A was supplied across the electrodes.X-ray diffraction measurements were performed using a Rigaku RAD Ill-B diffractometer (Cu-Ka radiation, 1.5418 A), The Carbonaceous deposits were mechanically milled, moistened with ethanol, and set in a sample holder prior to the XRD measurements. TEM observations of the milled powder confirmed that the carbon nanotubes and gigantic fullerenes were not damaged by the mechanical action of the milling operation. The carbonaceous deposits formed on the negative electrode were removed by sonication in ethanol for 10 s. This solution was then spread onto a collodion mesh and the HREM observations were carried out using a JEOL JEM-2000FX TEM operated at 200 kV. The samples were not cooled during the observations.