Study Of Novel Carbon Nanotubes And Boron Nitride Nanotubes With Four-and Eight-membered Rings

Since the discovery of carbon nanotubes(CNTs)by Prof.Iijima in Japan in 1991,the preparation and characterization of CNTs and boron nitride nanotubes(BNNTs)have been one of the research hotspots for nanomaterials.It is well known that the electronic properties of the CNTs composed of six-membered rings have a strong dependence on their structures.That is,the six-membered rings CNTs with different diameter,number of wall and chirality will exhibit the characteristics of metal or semiconductor.Besides,it is difficult to achieve the macro-preparation and separation of CNTs with certain conductance(metallic or semiconducting)in experiment.However,BNNTs are difficult to apply directly to semiconductor devices due to their wide band gap,which does not meet the requirements of the third generation of semiconductor materials.Therefore,by changing the configuration,novel CNTs and BNNTs composed of four-and eight-membered rings(novel CNTs and novel BNNTs)were studied by density functional theory(DFT),and their stability and electronic properties were discussed.The main contents in this paper are as following:The first chapter summarizes the application and research status of CNTs and BNNTs,and explains the research content and significance of this article.The second chapter introduces the DFT,the Gaussian03 calculation software and the base set used in this paper.In the third chapter,the stability and electronic properties of novel CNTs were studied.Among them,the emphasis is on the electronic properties of novel CNTs.The main conclusions are:The C-C bond of novel carbon tubular cluster(CTCs)and CNTs shows single or double bond,and the range of bond length is 1.34?-1.52?;The atomic hybridization of novel CTCs and CNTs is both sp2,showing a local smooth planar structure.It indicates that the structure of the novel CTCs and the corresponding CNTs is stable.The thermal properties show that the novel CTCs have high stability.The analysis of the average E_b shows that the stability of novel CNTs will increase with the diameter increasing.In particular,the study of the electronic properties shows that the band gaps of the novel CNTs are zero,exhibiting the metal properties,namely their electronic properties are independent of their diameter,number of walls and chirality.In the forth chapter,the stability and electronic properties of novel BNNTs are studied.The main conclusions are as following:The novel BN tubular clusters showed a single bond between B and N,with a bond length of about 1.452?;Thermodynamic properties showed that the novel BN tubular clusters have high stability,and the analysis of Eb showed that the stability of novel BNNTs will increase with the diameter.The electronic properties of novel BNNTs showed that the band gap of novel BNNTs is significantly reduced into the range of 2.530-3.975 eV,exhibiting semiconducting properties and fully conforming to the third-generation semiconductors'band gap width requirements,i.e.,more than 2.5 eV.Furthermore,the band gap monotonically decreases with increasing wall number.The fifth chapter is the summary and prospects of this article.