The Preparation And The Calculations Of Energy Bands And Electron-Emission For Carbon Nanotubes

The preparation, purification, structural simulation, energy band calculation and electron-emission calculation of carbon nanotubes are studied principally in this paper.The preparation for CNTs of high quality is the basis of their theoretical and application study. Consequently SWNTs are prepared through plasma arc discharge method, and in this method graphite powder is used as raw material, Fe/Co/Ni as catalyst, FeS as growth substance, H₂/Ar as buffer gas. Furthermore SWNTs are purified with chemical liquid oxidation method. The results of the electron microscope analysis indicate that the experiment of SWNTs is successful, and this may present useful experiences for further experimental study. In this paper, the geometry of SWNTs is simulated realistically by computer simulation.Band theory of solid is the one of the most successful theories in condensed state physics, and in principle most basic physical properties of solid can be illustrated and explained by the band theory of solid which is especially effective in explaining the properties of metal and semiconductor. Consequently by building tight binding model, using quantum theory and solid theory, the equations of π electron energy band of Zigzag SWNTs and Chiral SWNTs are deduced, and with the periodic boundary condition and the Bloch theory their band curves in the reduced Brillouin Zone are obtained. Analyses on the curves indicates that for Zigzag SWNTs only when structural parameters (m, n) satisfy the condition(m or n=3J, J is integer), there are zero points in the band curve of π electron, which proves in another aspect that when the structural parameters of SWNTs satisfy the condition(m-n=3J, J is integer), the SWNTs are metallic, or else semi conductive.Because of the excellent field-emission properties of CNTs they are applied to be scanning probe and consequently great attention has been paid to the their application in electron microscope area. In this paper by building free electron model, using quantum theory, solid theory, and statistic theory, the equations of electric current density(or current) of field-emissionof CNTs are deduced, and the curves of electric current density related to field strength are obtained. The results indicates that with the field strength improving, the current density grows sharply, which just proves that CNTs have a big field-emission current. Through calculation on field-emission of CNTs, excellent field-emission property of CNTs is proved theoretically, which provides the theoretical references for applications of CNTs on electron microscope area.