High-density production of carbon nanotubes in contact arc-discharge at low helium pressure

We report here on the structural properties of carbon nanotubes prepared by contact arc-discharge at low helium pressure of 100 torr. In contrast to the conventional arc-discharge, the contact discharge reduces the gap between the electrodes to a minimum value while still maintaining a plasma. The resulting carbonaceous deposit on the cathode surface, with the contact discharge operating under 100 torr helium atmosphere, contains the columnar structures with high density carbon nanotubes. These columnar structures are several millimeters in length, much longer than those generated under the conventional arc-discharge. These experimental results reveal that reducing the gap adds greater stability to the arc-discharge and establishes conditions that favor high-density nanotube growth under a low helium pressure.