Coupling Physical And Mechanical Properties Of Low Dimensional Structures And Devices

At nanoscale, many kinds of materials and structures have superior mechanical, electronic and chemical characteristics and the advanced functional nano-elements become more and more important in potential applications. Atomistic simulations have been played important roles in scaling down to nanoscale and can help in the elucidation of their properties and in the development of new methods for their fabrications and applications. In the thesis, exceptional properties and behaviors and the coupled effects of low-dimensional materials and structures have been investigated by using the atomistic methods including molecular mechanics and quantum mechanics as well as the continuum theory.Using the semi-emprical quantum mechanics as well as quantum-molecular dynamics techniques based on the Roothaan–Hall equations and the Newton motion laws, we have investigated the coupled mechanical and electronic behaviours of single-walled open carbon nanotubes (CNTs) under applied electric field and tensile loading. Different failure mechanisms and mechanical properties are found for CNTs subjected to electric fields and that subjected to tensile load. Electronic polarization and mechanical deformation induced by an electric field and tension load can significantly change the electronic properties of a CNT. The coupling of mechanical and electrical behaviours is an important characteristic of CNTs. Mechanisms for converting electrical energy into mechanical energy are essential for the design of diverse nanoscale devices such as sensors, actuators, artificial muscles, robotics, optical fiber switches and so on. Materials having special piezoelectric, electrostrictive and electrochemical properties play important roles in conversion between electrical and mechanical energy. Our researches have found that single-walled carbon nanotubes have exceptionally high axial electrostrictive deformation using ab initio and density functional quantum mechanics simulations.Both armchair and zigzag open-ended tubes and a capped tube are modeled and in all of them external electric fields induced axial strains can be greater than 10% for field strength within 1V/?. The corresponding volumetric and gravimetric work capacities are predicted to be three and six orders higher than that of the best known ferroelectric, electrostrictive, magnetostrictive materials and elastomers respectively.Multiwalled carbon nanotubes (MWNTs) have broad prospects as components in nanomechanical devices due to many exceptional electrical and mechanical...