Physical Mechanics Properties And Devices Of Carbon And Boron Nitride Nanotubes

Carbon nanotubes (CNTs) and boron nitride nanotubes (BNNTs) are expected to have great potential applications in building nano devices due to their unique geometry structures and excellent physical, mechanical and chemical properties. Atomistic simulation is a very powerful tool to unveil the complex phenomena in nanoscale and is also helpful for designing new nano devices. In this thesis, exceptional physical mechanics properties and behaviors of CNTs and BNNTs are investigated by using the atomistic methods including the molecular mechanics (MM) and quantum mechanics (QM) as well as the hybrid QM/MM method. The main contents are as follows:1) High frequency longitudinal oscillation of carbon nanotubes. To check the validity of the classical mechanics methods and to study the influence of electromechanical coupling effect on the oscillation behavior, longitudinal oscillation of a (3, 3) CNT is studied by ab initio quantum mechanical molecular dynamics (ab-MD) simulations. It is found by the ab-MD simulations that axial electric field affects very slightly on the longitudinal oscillation behavior of the CNT, but electrical charging can significantly influence the oscillation behavior. Classical MD method can goodishly describe the frequency-domain characteristic of the oscillation, but it can not exactly predict the electromechanical coupling effect, especially when the CNT is electrically charged. Choosing suitable mechanical parameters, both the simple spring-mass model and the hollow rod model can yield good prediction for the fundamental frequency, but can not give accurate descriptions for the higher order modes. Furthermore, based on the high frequency longitudinal modes of the CNTs, a terahertz (THz) source is also proposed.2) Density functional theory studies on the electric-field-induced deformation of BNNTs. Intelligent materials with high work density are essential for nano electromechanical devices. Our density functional theory calculations indicate that the electric-field-induced deformation of zigzag BNNTs can be 4% around field strength of 1.2 V/?. The corresponding volumetric work capacity is nearly ten times higher than those of the best reported polymer intelligent materials, and about 3 orders of magnitude higher than those of traditional piezoceramics. The large electric-field-induced deformation is found to arise from both the converse piezoelectric effect and the electrostrictive effect of BNNTs. Considering the high chemical and thermal stability and electrical insulation, BNNTs they should have great value in potential applications. 3) Quantum mechanical molecular dynamics simulations of nano-gun from CNTs. How to make nano/molecular machines work is a challenging nanotechnology issue, especially to drive magnetoelectrically neutral molecules. Here, we demonstrate by quantum mechanical molecular dynamics simulations on an ideal model that an electrically neutral nanotube or fullerene ball inside a one-end-open carbon nanotube can be driven into movement by properly charging the housing nanotube. It is more interesting that positively charged housing tube can drive the molecule inside it out, like a nano-gun; while negatively charged housing tube can only drive the molecule into oscillation inside it, but can not drive it out. Instead, a negatively charged housing tube can absorb inward a neutral molecule in the vicinity of its open end, like a nano-manipulator. These findings may be helpful for designing new nano devices.