Design And Development Of A Carbon Nanotube Based Microfocus X-ray Tube

Microfocus X-ray tube plays an important role in scientific research andapplication of modern medical science, biological science, industrial testing and so on.Due to hot cathode electron source, the traditional microfocus X-ray tube has manydisadvantages such as large volume, start slowly, low temporal resolution, lowefficiency and short lifetime, has already can’t satisfy the requirement of modernscientific research and technology applications. The carbon nanotube (CNT) isrecognized as an ideal field emission electron source having excellent electron emissionperformance. To replace hot cathode, using carbon nanotube field emission cathode inX-ray tube which was consided one of the "shake the world" applications of carbonnanotube can develop a low energy consumption, high resolution, impulse response andextending lifetime miniature X-tube. In this paper, carbon nanotubes emitter arrays withexcellent field emission performance were fabricated using microwave plasma chemicalvapor deposition (MWPCVD) by optimizing the structure of catalyst, annealing andaging. A carbon nanotube based microfocus X-ray tube was developed throughsimulation design and experimental study. The main research contents are as follows:(1) The morphology and field emission performance of carbon nanotube arraysgrown by five different kinds of stack type catalyst structures of Ni/Al/Fe, Ti/Al/Fe,Au/Al/Fe, Cu/Al/Fe, Ti/Cu/Al/Fe, were studied. Uniform, well-vertical aligned andgood adhesion with substrate CNT emitter arrays was synthesized by employingcatalyst structures of Ti/Cu/Al/Fe. Field emission characteristics of CNT emitter arraysshowed very low turn-on electric field, emission threshold electric field and stableemitting. A maximum field-emission current of255mA，corresponding a currentdensity of1.04A/cm2were obtained.(2) Less lattice defects, single straight carbon nanotube emitter arrays were grownon molybdenum (Mo) substrate using a stack catalyst structure of Ti/Cu/Al/Fe. Due to aall-metallic contact be formed through a Ti/Cu buffer layer between CNTs and Mosubstrate, CNTs had a good adhesion and conductivity with Mo substrate. Compared Sisubstare. Field emission characteristics test showed that Mo substrate can enhance field emission performance of CNTs and had a stronger resistance to ion bombardment.(3) Annealing on the improvements of morphology and field emission performanceof CNTs were studid. Annealing is not only able to get rid of the impurities in CNTsbundles, but also reduce the lattice defects of CNTs and make it more straight by furthercrystallization in high temperature. CNTs also become a better adhesion to substrateafter annealing than before. Field emission testing showed that, after annealing, CNTsarrays had a lower turn-on electric field and a higher field emission current.(4) Aging on improvements of morphology and field emission performance ofCNTs were studied. Some CNT with many lattice defects could be removed by strikingin a small field current, which stable the field emission current of CNTs emitter arrays.(5) A carbon nanotube based microfocus X-ray tube was designed and simulatedusing CST particle studio. Such parameters as geometrical distance and applied voltageamong all the electrodes are considered, respectively, in relation to the size of X-rayfocal spot. A CNT based field emission X-ray tube has been constructed in experimentbased simulated model after optimized. A small focal spot size of35μm×32μm wasobtained which agree well with the simulation date.