Preparation And Performance Of Field-emission Devices Based On Carbon Nanotubes And Their Composite Cathodes

In recent years,there have been increasing number of reports about field emission devices,in which the field emission display（FED）drawn much attention,in particular.It is significant for researchers to choose proper field emission cathode materials.Among the varieties of cathode materials,films based on carbon nanotubes and their composites are thought to be the most valuable and significant materials.In this work,the field emission properties of carbon nanotubes and their composite films was studied.At first stage,the field emission properties of pure carbon nanotube films are investigated.Subsequently,the field emission properties of their composite films with molybdenum disulfide are studied as well.The details are as follows:（1）Field-emission study of carbon nanotube filmsPure carbon nanotube films with enhanced field emission performance was fabricated by using vacuum filtration followed with double-sided conductive tape.By adjusting the concentration of the carbon nanotubes dispersion solution,cracked carbon nanotube films with different morphologies were prepared.Subsequently,field emission performance of samples with various concentrations was tested.Based on the analysis of the characterization results,the reasons for the enhanced field emission performance are as follows:1)The double-sided conductive tape not only provides mechanical help for the generation of cracks,but also enhances the adhesion between the CNT film and the ITO glass substrate,improving the current density emission stability.2)The cracks enlarge the distance between most of the adjacent carbon nanotube emitters,which is helpful to reduce the field emission shielding effect between emitters.3)The tips of the carbon nanotubes exposed at the edge of the crack due to the surface fracture of the cathode film could serve as new current emission sites,boosting the average local electric intensity.Overall,thanks to the synergy of these factors,the cracked CNT cathode field emission device exhibits excellent field emission performance.（2）Field-emission study of MoS₂/CNTs composite filmsIn order to obtain a sort of enhanced field emission performance cathode film,we set our sights on a wider range to find out the field emission properties of molybdenum disulfide,one of the most popular two-dimensional materials.In addition,by compounding molybdenum disulfide with carbon nanotube,cathode films with excellent field emission performance were attained.Comparing the field emission performance of cathode films with different mass ratios,we conclude that the reasons for the enhanced field emission performance of the molybdenum disulfide/carbon nanotube composite film are as follows:1)After combining CNT with MoS₂,the interlayer distances of MoS₂ in the cathode film is increased,forming a three-dimensional spatial structure between MoS₂ and CNTs,which provides more efficient field emission areas.2)The unique MoS₂ nano flower structure with a large number of thin and sharp edges provides more emission sites for field emission.3)A reasonable composite mass ratio of CNT and MoS₂ provides an appropriate number of emitters and reduces the field emission shielding effects.