Investigation of growth conditions of fibrous deposits in carbon arc
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Investigation of growth conditions of fibrous deposits in carbon arc P. Byszewski Institute of Vacuum Technology, Długa 44/50, 00-241 Warsaw, and Institute of Physics, PAN, al. Lotnik´ow 32/46, 02-668 Warsaw, Poland
K. Ukalski Institute of Vacuum Technology, Długa 44/50, 00-241 Warsaw, Poland
E. Mizera Institute of Physics, PAN, al. Lotnik´ow 32/46, 02-668 Warsaw, Poland
E. Kowalska Institute of Vacuum Technology, Długa 44/50, 00-241 Warsaw, Poland (Received 9 June 1995; accepted 17 June 1996)
Carbon fibrous deposits grown in carbon dc electric arc at various buffer gas pressures and arc currents were investigated by transmission and scanning electron microscopy. The fibers contained in the deposits consisted of bundles of carbon tubes. It was found that yield and morphology were very sensitive to both parameters; sintering of the tubes could be prevented by adjusting buffer gas pressure for a given current. It is argued that these parameters control expansion of carbon gas and condensation rate, and therefore energy flow to the cathode. To purify samples by oxidation and to observe differences in resistance against oxidation of samples obtained at various conditions, the thermogravimetry method was used.
I. INTRODUCTION
The multishell carbon nanotubes consist of several concentric rolled graphene planes,1 and the diameter of the tubes ranges from nanometers to almost macroscopic size.2 The tubes can be grown in dc arc plasma in He atmosphere in the cathode deposits, using either graphite1 or amorphous carbon3 electrodes, or by decomposition of hydrocarbon compounds in carbon arc plasma.1,4,5 In the electric arc process, the cathode deposits consist of “columns” aligned parallel to the cathode, and nanotubes are contained in the columns. Continuous growth of the tubes requires maintaining dangling bonds at the growing tip and a stable supply of carbon complexes. It was proved by the computer simulations6 that the growth of the tubes could be modeled as condensation of monoatomic carbon gas with different in-graphene plane and out-of-plane attachment energy, though in other models, growth from the liquid consisting of carbon clusters7,8 was considered. For the directional growth of the tubes along the cathode, it is believed that extremely high electric field at the cathode9 or the temperature gradient at very efficiently cooled3 cathode is responsible. II. EXPERIMENTAL
The ideal arrangement for controlled growth of carbon nanotubes would require controlling thermal and electrical conditions in the microscopic scale, i.e., at J. Mater. Res., Vol. 12, No. 6, Jun 1997
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the tip of the single tube. This, however, is beyond our means for growth of carbon nanotubes proceeds in the arc in very turbulent environment. To acquire more information on the problem, we investigated the influence of macroscopic parameters on the efficiency of the processes. In the electric arc most of the energy is lost due to radiation from
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