Preparation Purification And Field Emission Calculation Of Single-walled Carbon Nanotubes

The preparation, purification and field emission calculation of single-walled carbonnanotubes are researched in this paper.Since 1991 when S.Iijima discovered the carbon nanotubes, the high tide to research thecarbon nanotubes has been aroused in the universal science and technology area. Especiallythe property, preparation method and application foreground have been a hotspot. The maincontent of this paper are as follows.The structure, property, application and the three main preparation methods(plasma arcmethod, laser vaporing method and catalyzer decomposing method) are introduced in thesummary.In the preparation of carbon nanotubes, the synthesis is carry out by plasma arc method,and the chemical method is adopted to purify the production which is obtained from formerstep. In the experiment, Fe, Co, Ni as the catalyzer, H₂ and Ar as the buffer gases, and S as thepromotive reagent are used. In order to make the stuff easily become a mass, the grinder isused to process it, and we get an expected result. In the purification process, the two mainsteps(HCl and K₂Cr₂O₇ with H₂SO₄ scheme) are introduced to purify the obtained productionstep by step. And the comparison between two TEM photos(from productions which ispurified and which is not purified) intuitionisticly proves that the effect of purification isevident. The TEM photos tells us that carbon nanotubes distribute equably and clearly, whichillustrates that the synthesis and purification are feasible.In the calculation of field emission, basing on Maxwell electromagnetic theory, thephysical model, the corresponding mathematic equation and the boundary condition are raised.The electric field near the tip of metallic single-walled carbon nanotubes is calculated and theexpressions of electric potential, electric strength and field enhancing factor are deduced. Onthis base the distribution curves of the electric potential and electric field strength near the tipof single-walled carbon nanotubes of different lengths and diameters are calculated out, and the function curves of field enhancing factor according to length, diameter and the distancebetween two electrodes are computed out for single-walled carbon nanotubes of differentgeometrical size. Analysis tells that for a nanotube which has a fixed length and diameter,along the direction of radius and axis of the nanotube the electric field strength drops sharplywith the distance away from the tip increasing, and it is proved that the stimulated electricfield from single-walled carbon nanotubes is a strong field of limited range; the fieldenhancing factor of single-walled carbon nanotube is linearly increasing with its lengthincreasing, and decreasing sharply with its diameter increasing; single-walled carbonnanotube has a quite low threshold voltage and high field emission electric current density asa field emission cathode. The results of this paper provide a theoretical reference for thesingle-walled carbon nanotubes to be an ideal field emission material.