Research On Simulative Calculation Of Field Emission Properties Of Carbon Nanotubes

Carbon nanotube is a new kind of nanometer material, having a high surface area, smallradius of curvature of the tip, high chemical stability, low field emission threshold voltage,large current density, is widely considered to be an ideal material for electron emission.However, because many problems as emission sites density and uniformity of carbonnanotube are still exist, which greatly limits its application in the commercial aspect,therefore to research the field emission mechanism of carbon nanotube and seek the methodto enhance and improve field emission properties is very important and necessary.In this paper, we simulated and researched the field emission properties of carbonnanotubes on atomic scale by using first-principles density functional theory. In view ofmethod to improve the field emission performance of carbon nanotubes at present, we studythe influence of hydrogen and sodium adsorbed capped and uncapped carbon nanotubes onfield emission properties.In the third chapter, the field emission properties of hydrogen adsorbed capped anduncapped carbon nanotubes were studied using first-principles density functional theory. acapped and uncapped (5,5) carbon nanotubes model with different hydrogen adsorbed werebuilt, and the adsorption energy, HOMO-LUMO band gap, the induced dipole moment of themodel with and without the applied electric field were calculated and analyzed. Thecalculation results are explained the presence of hydrogen molecules adsorbed in experimentsthat electrons emit more easily, and revealed carbon nanotubes field emissionmechanism,which can improve carbon nanotube field emission material significantly.In the fourth chapter, using first-principles density functional theory,we haveinvestigated the electronic and field emission properties of carbon nanotubes with Na atomsadsorbed. a capped (5,5) carbon nanotubes model with different Na atoms adsorbed werebuilt, and the adsorption energy, ionization potential, local density of states, Mulliken chargepopulation of the model with and without the applied electric field were calculated andanalyzed.The calculation results show that carbon nanotubes adsorbed Na atoms, thestructure changes, and there are almost no effect on the structure of carbon nanotubes withand without the applied electric field. Through these models analysis shows that adsorption energy as the field increases, and the adsorption stability enhancement. For pure carbonnanotubes and Na adsorption on carbon nanotubes system, in the electric field cases,ionization decreased, indicate that the field emission properties are improved, the electronicemitting more easier. Local density of states at the Fermi surface analysis can be seen in thelocal density increased. The Mulliken charge population analysis shows that, the charges areredistributed and accumulated on the tip. Our results reveal the role of Na moleculesinenhancing the field emission properties of carbon nanotubes,and provide the possiblefieldemission mechanism,which can guarantee the application of carbon nanotubes to fieldemission devices.