Field emission from teepee-shaped carbon nanotube bundles

Carbon nanotubes were fabricated close together so that their separation is smaller than their height and field enhancement effects at the apexes of the tubes are diminished due to electrostatic shielding. Bundling was achieved by embedding the tubes into a PCVD silicon dioxide, followed by HF etching, water rinsing, and nitrogen drying. Emission measurements were performed in a vacuum system at a pressure of 4 /spl times/ 10/sup -9/ Torr. Current-voltage characteristics were obtained at room temperature, 120 /spl deg/C and 170 /spl deg/C. Macroscopic current densities of /sup 2/0 mA/cm/sup 2/ were obtained with a 0.5 mm diameter tungsten anode. The turn-on fields are about 15 V//spl mu/m.