The Microstructures Derivation And Electronic Properties Of Chiral Carbon Nanotubes

CNTs has been widely application in biological engineering,medical carrier,hydrogen storage.Structural changes in carbon nanotubes(CNTs)alter electronic properties of these structures at the atomic scale.In this work,we simulate the morphology of nuclear structures.We establish the “open at one end and closed at another end growth” model by the first-principles density functional theory(DFT)to investigate the growth mechanism and the electronic properties of these CNTs of chiral CNTs,namely,single-,double-,and triple-walled CNTs.The main research content and conclusions are as follow:1.Chiral CNTs are obtained through layer by layer absorption of Cd'atoms,and Mulliken charge distribution is used to explain the localization of the growing point at the open end.And multi-walled CNTs follow the “from outer layer to inner layer” growth mechanism.2.Analysis of average binding energyEb(l)showed that carbon atoms at the open end is energetically metastable compared with ones in the perfect hexagonal carbon network,which results in the increase of Eb as the tube length increases since the ratio of carbon atoms at the open end to all carbon atoms decreases.3.The growth of infinitely long CNTs obtained by imposing the periodic boundary conditions(PBC)depend on corresponding nuclear structures.Analysis of band structure showed that energy gaps are caused by the curvature of tube walls,and they become increasingly remarkable as diameter decreases.(1)For chiral infinitely long SWCNTs we investigated,a semiconductor is produced when n-m ? 3q,whereas a conductor is produced when n-m = 3q;(2)For chiral(n1,m1)@(n2,m2)DWCNTs we investigated,a semiconductor is produced whenn1 –m1 ? 3q @n2 –m2 = 3q,whereas a conductor is produced when n1 –m1 ? 3q @ n2 –m2 ? 3q(or n1 –m1 = 3q @ n2 –m2 = 3q);(3)For chiral(n1,m1)@(n2,m2)@(n3,m3)TWCNTs we investigated,a conductor is produced when n1 –m1 ? 3q @ n2 –m2 ? 3q @n3 –m3 = 3q(or n1 –m1 = 3q @ n2 –m2 = 3q@n3 –m3 = 3q).The simulated nuclear structures and growth process better elucidate the mechanism of chiral CNTs formation in experiments,and they serve as guide in controllable production of chiral CNTs at the industrial level.