Time-Dependent Response of Field Emission by Single Carbon Nanotubes

Four field emission tubes that have single carbon nanotubes (CNT) as the emitters were tested; two with single-walled CNT and two with multiwalled CNT. A tube with a tungsten tip was used for comparison. Fowler-Nordheim analysis of the DC current-voltage data gave reasonable values for the local fields at the emitters and the sizes of the emitters. Two oscillators were used to superimpose sinusoidal signals on the applied static field, thus increasing the DC emitted current and causing a mixer current at their difference frequency, in agreement with theory. Square-wave pulses from a single laser diode (20 mW, 658 nm) focused on each emitter increased the emitted current by 5.2% with the CNT and 0.19% with the tungsten tip.