以第一原理探討BC(2)N奈米管之場發射特性

Abstract

By first-principles density functional theory, we investigate the field emission properties of the infinite BC_2 N nanotubes with various tube diameter, or different number of carbon and boron-nitride atomic layers. The zigzag and armchair BC_2 N nanotubes with lower work function than the graphite and hexagonal-BC_2 N display excellent field emission properties. For the zigzag structures, ZZ-1(8,0), ZZ-2(9,0) and ZZ-3(8,0) are tube sizes with the best field emission property respectively. And decreasing the diameter of zigzag BC_2 N nanotubes will decrease the Fermi energy and increase the work function, different to the concept of the super tip. Although the armchair structures show low work function with small diameter, they are not better than zigzag structures on field emission properties. By changing the number of C/C and B/N atomic layers, it is found that the ZZ(8,0) with three atomic layers exhibits better field emission property, and the work function of the AC(6,6) with two atomic layers is higher than the others. Therefore, the field emission properties of armchair structures can be improved by increasing number of C/C and B/N atomic layers up to three atomic layers or more. The BC_2 N nanotubes show the better field emission properties than carbon nanotubes and nitride-boron nanotubes due to the elements B, N and C from the B/C and N/C bonding layers. Besides the energy gap of the tubes, the binding forces from another atoms observed by band structures will also affect the work function. Comparing the elements of C/C and B/N atomic layers of BC_2 N nanotubes, the carbon atom near boron atom can contributes much more electrons than the others during the field emission. From the analysis of the total density of states, it is found that if there are more orbital close to the level of Fermi energy, more electrons can be emitted. In other words, more field emission current can be achieved. Therefore, the BC_2 N nanotubes are suitable to be adopted as one of field emission sources.