Carbon Nanotube Array Preparation And Field Emission Characteristics Of Study

The discovery of carbon nanotubes attracts many scientists'attention. Carbon nanotubes can be used in many fields due to its excellent mechanics, electricity and magnetic. Carbon naontubes have a high ratio in length-radius, low work function, good electrical conductivity and nanometer tip. It can emit electrons at low voltage. So it has been considered a good field-emission cathode and has been used in electron beam device such as SEM, TEM, microwave devices, field emission display (FED) and so on.Firstly, in this paper we explored and researched the process of gorwing CNTs bundle array by microwave plasma chemical vapor deposition (MWPCVD). We grew CNTs bundle array by depositing Fe onto the Si chips. The effects of growth temperature, the type of catalyst, the thickness of catalyst, the proportion of mixed gases and substrate materials to growth of CNTs were studied in detail. Then, these work layed the foundation for fabricate carbon nanotube bundle field emission arrays (FEAs) in a large area.Furtherly, we fabricated carbon nanotube bundle arrays successfully, whose size was less than 3μm in diameter. The grown CNT bundle array was orderly and uniformity. Comparing the single CNT for the emitter unit, the CNTs bundle emitter not only overcame the problem of directional growth of CNT but also improved the field emission performance of CNT-FEA. The measurement results of the field emission behavior indicated that the electric field was 4.11V/μm and the current density reached to 4mA/cm2;When electric field reached to 8V/μm,the maximal current density was 1.352A/cm2.Finally, we studied the space charge effect in CNT field emission and the influence to field emission behavior by CNT array density. We built a model of prepared carbon nanotubes bundle arrays and the emission current density in different CNT density is simulated by Electron Beam Simulation (EBS). The simulation results shown: When the density was too much tightness,neighboring CNT would affect each other,so the total emission electric field was reduced. When the density is too much poor,the emission current density was also reduced eventhough the emission current of single CNT was increased, because the number of CNT on unit area was reduced. The result shown that when the length of CNT was 4μm,the optimal space between each CNTs was 1μm. Thus,the space between each CNTs was a quarter of the length of CNTs,that was the best density of the CNTs array. The influence of the space charge effect in the character of carbon nanotube field emitter was simulated also using EBS software, including the distribution of electric field on the surface of emitter, emission current density, I-V behavior and the expending angle of emitting electron beam. We got the conclusion:the surface electric field was restraind by space charge effects; as a result the current density of carbon nanotube was limited. Then the space charge can lead the expending angle of emitting electron beam to be larger by influencing electronic tracks.