High current/high current density carbon nanotube cold cathodes

Field emission measurements on individual carbon nanotubes grown by dc plasma CVD at 700°C have been performed with a high resolution scanning anode field emission microscope. I-V characteristics of as-grown CNs show a saturation for currents above 1 μA and the maximum emission current is in the range 5-10 μA. This saturation is attributed to a bad CN/substrate contact. By improving this electric contact by thermal annealing at 950°C, the saturation is suppressed. To improve emission current density, the effect of CN density on maximum emission current is studied. For this purpose, 0.5 × 0.5 mm² arrays of vertically aligned CNs with a 1.5 μm height, a 15 nm diameter and a 3 μm spacing are grown. The CN density is 10⁷ cm^-2. CNs exhibit almost the same aspect ratio [200] but the CN density is increased by a factor of 10. From such an array, an emission current of 10 mA corresponding to a current density of 4 A cm^-2 is measured.