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High current density cathodes

The carbon nanotube cathode is an array of individual and vertically aligned carbon nanotube (CN) array. A typical array includes 5µm height and 50 nm diameter CNs. The pitch between two neighbouring CNs is equal to twice the CNT height i.e. 10µm. Typically, the standard deviation in the radius and height distributions of the CNs is 4.1% and 6.3% respectively so that the aspect ratio (h/r) of most of the nanotubes in the array is around 200 +/- 7.5%.

After a dedicated post treatment process (E. Minoux, et al., "Achieving High Current Carbon Nanotube Emitter", accepted for publication in Nano Letters (2005)), each nanotube of the array is capable to emit a current of 100 +/-20µA. The maximum current density for an array operated in DC mode is around 1.5A/cm2 and becomes 12A/cm2 when this cathode is operated at 1.5GHz (K. Teo et al., Nature 437, 968 (2005)).
Recently, we fabricated an optimised array made of 1.5µm height and 30nm diameter CNs (pitch = 3µm) that delivers a current density of 4A/cm2 in continuous mode.

Such high-density cathodes should find application in microwave amplifiers but also in X-ray tubes.

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Research Dept.
Thales R&T, RD 128
91767 Palaiseau
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