Fabrication of carbon nanotube tips for a high-brightness microfocus X-ray tube

Abstract

A high brightness microfocus x-ray tube requires a high brightness electron beam with a diameter under 5 μm and current over 25 μA to reach the x-ray target. As a electron beam source, carbon nanotube (CNT) on tungsten tip was used. For the fabrication of CNT on tungsten tip, two methods were used: dielectrophoresis and ICP-CVD (Inductively Coupled Plasma Chemical Vapor Deposition). Dielectrophoresis is a useful technique that can manipulate and assemble small objects into predetermined patterns by interactions between the external electrical field and the induced dipole moment. Optimized fabrication of CNT was made using various parameters such as the initial conditions of the CNT, the distance between tip and the electrode, dc voltage. ICP-CVD uses plasma and has concept of development to optimize carbon nanotube fabrication. Ni was used as a catalyst and TiN was used as buffer layer and CNT was then fabricated by it. The fabrication of short carbon nanotube tips by dielectrophoresis and ICP-CVD is reported in this paper. Alinged CNT tips comprising either singlewall carbon nantube (SWNT) bundle or multiwalled nanotubes (MWNT) of controlled length and orientation were assembled. Beam generation was evaluated, using CNT as an electron source and phosporous screen as an anode. Simulation of electron beam track and current generated from CNT were evaluated. The result of electron beam generation using CNT tip as a first step for a high brightness microfocus x-ray tube is reported.