الفهرس 
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Abstract
This work is classified as follows:
With the development of fabrication technology in nanometer materials, heterojunction CBNNTs formed between nanotubes recently synthesized. However, the behaviors of resulting heterojunction CBNNTs as stability, growth, and electronic structures are still unknown. This information is necessary when designing optimal synthesis procedures for these structures and for understanding their resulting properties, which may be tuned for specific applications. Therefore in this thesis theoretical study of density functional theory for three system, pure carbon nanotubes (CNTs), pure boron nitride nanotubes (BNNTs), and heterojunction carbon boron nitride nanotubes (CBNNTs), has been investigated in order to understand the differences in stability and electronic structures between the three systems. The effects of diameter, chairity, ways of BN-distribution, and length of tubes are included. Also, the monovacancy defects are explored in details for three systems, especially our concern system CBNNTs.
Our main outcomes show that the important role of monovacancy defects is to modify the electronic structures of CBNNTs, in addition other parameters, as the diameters, length of tubes, ways of BN-distribution through CNTs. The band gap can be reduced from 5.88 eV for BNNTs to 0.25 eV by BN-row distribution in (9,0)CBNNTs(1:5), i.e, the band gap is reduced by ~ 96%.
Both of molecular orbitals and density of states are used for analyzing the results.