| Carbon nanotubes (CNTs) with unique properties of high aspect ratio, low work function, high mechanical strength and thermal conductivity, have been considered as promising materials for application of field emission devices. However, the field emission properties of CNTs, such as electron emission density, stability and. uniformity are not yet satisfied for electron source application. On the other hand, the preparation methods of traditional rigid field emission devices are also not suitable for preparing the next generation field emission devices (flexible devices). Thus, it is crucial to improve the field emission properties and optimize preparation methods for their practical applications. In this work, a series of studies were proceeded round CNT based composite field emission cathodes, field emission under low vacuum and optimization for the fabrication processes of flexible devices with purposes of systematically improving the field emission properties, extending the application of field emission to low vacuum and optimizing the fabrication processes of flexible field emission devices.The work mainly includes the following aspects:(1) The CNT/TiO2 composite films with outstanding field emission properties were prepared by spin coating titanium dioxide sol onto screen printed CNT film. Compared with CNT film, the field emission performances of composite film were obviously improved, including the dramatically decreased turn on field and threshold field, the highly enhanced emission current stability. Besides, the field emission properties of CNT/TiO2 composite film were controlled by changing the reaction time of TiO2 sol and the thickness of TiO2 layer. The optimized sample with an ultralow turn-on and threshold fields of 0.383 and 0.657 V μm-1, corresponding with a high field enhancement factor of 20000 was achieved, as the best performance among the studies of CNT cathodes decorated with metal oxides reported so far. Furthermore, the improvement of field emission was also explained in this article.(2) The influence of gas pressure on field emission properties of CNT films under oxidizing gas (air) and non-oxidizing gas (nitrogen and argon) atmosphere was systematically studied. The field emission properties of CNT film decayed as gas pressure increased under both oxidizing gas and non-oxidizing gas. However, the field emission from CNT degraded more rapidly under oxidizing gas than under non-oxidizing gas. The influences from oxidizing and non-oxidizing gases were further explained with gas adsorption, gas ion bombardment and Joule heat mechanisms. Besides, the field emission properties of CNT film under low vacuum were dramatically improved by decorating TiO2 nanoparticle film onto CNT film which extends the field emission application of CNT film from high vacuum to low vacuum.(3) The field emission properties of CNT film were improved by mixing CNTs with a certain amount of graphene. By mixing graphene and CNTs, the contact barrier between CNT film and silver substrate was reduced and the electron transfer from substrate to CNT emitter became easier. Besides, the field emission properties of the graphene/CNT composite film were optimized by controlling the amount of graphene in composite film and comparing the preparing methods of composite film.(4) With the unique properties of PDMS, such as flexibility, transparency and strong adhesion, the all-carbon nanotube based flexible field emission devices were prepared in this study. Combining vacuum filtration with simple film transferring technique, the preparing method of all-carbon nanotube based flexible devices has advantages of low-cost, low temperature, low power consumption and organic impurity free. Besides, the influence of substrate deformation on field emission properties was systematically studied by testing the field emission performances of CNT flexible device under different bending directions and different bending radii. Furthermore, the influence of substrate deformation on field emission properties was explained. |
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