Electron field emission from a single carbon nanotube: effects of anode location

Abstract

Electron emission from an isolated carbon nanotube (CNT) were performed in-situ in a modified scanning electron microscope, over a range of anode to CNT tip separations, D, of 1 to 60 /spl mu/m. The CNT was exposed from a CNT-polymer composite which was physically broken and examined along the broken edge. The threshold required for an emission of 100 nA was seen to decrease from a value of 45 V/spl mu/m/sup -1/ at an anode to CNT tip separation of 1 /spl mu/m, and asymptotically approaches 4 V/spl mu/m/sup -1/ at a separation of 60 /spl mu/m. By defining the separation as (D-h) rather than D, where h is the height of the CNT, our applied electric is E=V/(D-h). Calculation of enhancement factor using the Fowler Nordheim equation shows an increase in enhancement factor with an increasing D, and ties in well with the decrease in threshold with increasing D. Under far field conditions, where D > 3h, the CNT enhancement factor is no longer dependent on D as shown by the asymptotic behaviour of threshold field, and is purely a factor of the CNT height and radius. Fowler-Nordheim analysis allowed calculation of the emission currents for given CNT to tip separation. The calculated emission current, threshold and enhancement are comparable to that found experimentally.