Field Emission and Growth of Fullerene Nanotubes
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ABSTRACT
Efforts to control the growth of individual carbon nanotubes from nanotube seed crystals have led to a characterization of their field-induced electron emission behavior. The application of a bias voltage in our growth apparatus was motivated by the prolific formation of nanotubes in the carbon arc growth method, in which the electric field appears to play a central role. '2 We report here the ability to achieve various tube tip configurations by the controlled application of voltage, heat and chemicals to an individual nanotube, and that these states are well characterized by the emission currents they induce.
BACKGROUND Much progress has been made in increasing their yield, 3 and in purification, 4' 5 but substantial quantities of carbon nanotubes are still not generally available with a perfect graphene structure over sufficient lengths that they truly deserve the term fullerene fibers.6 For example, nanotubes are produced in great quantity by the carbon arc method, but appear always to contain defects over lengths beyond several microns. Attempts to ameliorate this have recently led us to propose a model for growth in the carbon arc, and to the conclusion that defects unavoidably arise from tubes' sintering together in the extreme heat of the arc.2 To circumvent this problem and to discern growth conditions which will yield defect-free nanotubes of any desired length we have engaged in experiments designed to perpetuate the growth of a single nanotube, starting from a nanotube seed crystal collected from the carbon arc deposit. In order to place our field emission results in context, it is useful to revisit some of our other more recent findings in this fast breaking field. A key feature of our carbon arc growth model is the synergetic relationship between the growing nanotubes and the arc plasma. Here the 10 V potential drop across the very thin (
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