| A carbon nanotube has a special hollow fiber structure, a very large specific surface area, which shows excellent physical and chemical properties, such as high strength, high elasticity, high toughness, excellent heat conduction and conductive ability, optical and magnetic properties, chemical catalytic properties and attracts widespread interest of physicists, materials scientists, chemists. More and more experimental and theoretical studies show that carbon nanotube as the representative of the nanotube material will play an important role in nano-electronic devices, displays, hydrogen storage materials, high-strength fiber material, photocatalyst, ceramic materials, and construction materials field.Boron nitride nanotube is another nanotube material after carbon nanotube was discovered which has similar structure of hollow. And the surface consists of hexagonal tube, where the B and N atoms have a sp-hybridization, similar to carbon sp2hybridization in a graphite. Boron nitride nanotube has different electrical properties from carbon nanotube. The band gap of carbon nanotube is sensitive to diameter and chirality, showing the change from metal to semiconductor electrical properties. But the band gap of boron nitride nanotube is always5.5eV regardless of their diameter and chirality, so the boron nitride nanotube shows stable electrical properties. Furthermore, the boron nitride nanotubes have some features different from the carbon nanotubes, such as:high temperature and oxidation resistance, making a broad application in electronic devices such as high temperature semiconductors, insulators, single electron transistors, gas storage, magnetic refrigeration and so on.Boron nitride nanotube is a relatively strong ionicity nanomaterial, the reactivity is weak, which make it not readily react with other chemical substances. However the doping modification can enhance the reactivity of the boron nitride nanotube, which can induced its semiconductor characteristics and achieve its function applications.Here, according to the progress of the current study have been carried out, we study three kinds of chirality boron nitride nanotubes doped carbon atoms with the density function method implemented in Gaussian09software. The geometrical structure optimization was achieved with HSE06/6-21G method, the band structure was calculated with HSE06/6-31G(?) method (based on the geometrical structure optimization). The calculated parameters include:bond length, bond angle, lattice constant, diameter, density of states, band gap, formation energy, Van Hove singularities and the consequent optical transitions.The results showed that the basic parameters of pure boron nitride nanotube are consistent with the previous data so our calculation method is reasonable. We find that:After the carbon atoms doped, the geometric structure of chiral boron nitride nanotubes show the most obvious change, while those of the armchair and zigzag boron nitride nanotubes change a little. The electronic structures of three kinds of nanotubes change noticeably with the change of the doped carbon atoms. The impurity peaks appear in band gap around Fermi level among density of states. The nanotubes doped odd number carbon atoms have spin density states. The intruduced atoms decrease the band gaps and improve the conductivity of boron nitride nanotubes, and the conducivity become better with the increase of carbon atoms. In addition, the doped atoms change the Van Hove Singularities in the density of states, so the optical transition width decrease and the optical transition improves. Although some results still need yet to be verified, the conclusions have greater significance for further study and reference value, which help us get a deep and comprehensive understanding of the electronical and optical properties of boron nitride nanotube. |
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