Constructing a field-emission (FE) x-ray tube

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This project was aimed at establishing a technique to prepare carbon nanotubes (CNTs) having a metallic filament inside. The results obtained are outlined as follows.1) Field anode growth (FAG)Usually, FAG-grown CNTs are filled with a metallic matter, but some CNTs are completely filled with a Cr wire, lengthening up to 10-15 μm. In general, CNTs grown on field anodes undergo a straight growth from the substrate, with a few exceptions. Typical exceptional cases are ; "bridging" CNTs connecting the adjacent CNTs and "child" CNTs grown from the side face of thick CNTs.2) Field cathode growthThis type of CNT growth needs Fe, Ni or Co as catalyst. The CNTs thus grown are always topped with a metallic nanocrystal, and are characterized by straight growth along electric field lines. The latter fact enables us to prepare the so-called "aligned CNTs, " which can serve as the field-electron source in an electron-beam tool. Recently, we successfully applied our aligned CNTs to the electron source of a compact x-ray tube, the result of which is to be published in the April-23 issue of Applied Physics Letters.3) Newest researchIn the last stage of this project, we noticed that, like Fe, Ni and Co, palladium (Pd) catalytically promotes the CNT growth on field anodes. This sort of CNTs are capped with Pd nanocrystals. The hydrogen-occlusion behavior of such Pd nanocrystals will be soon investigated at our laboratory.