Carbon nanotube cathodes for microwave and X-ray electron tubes

Carbon nanotube (CNT) cathodes are field emission electron sources, operate at room temperature and allows instant turn. The emitted current, which depends on the electric field at nanotube apex, can be modulated using a gate electrode. Recently, we proposed to use another method which is the optical control of a CNT photocathode. This photocathode is an array of vertically aligned multi-walled CNTs, each CNT being associated to a semiconducting p-i-n photodiode. Schematically, the p-i-n element acts as an optically controlled current source. This operating mode is particularly interesting for the two targeted applications which are X-ray tubes for 3D imagery and microwave tubes for satellite telecommunication.