Mechanical and electrostatic properties of carbon nanotubes under tensile loading and electric field

Coupled mechanical and electronic behaviours of single walled open carbon nanotubes (CNTs) under applied electric field and tensile loading are investigated by the use of quantum mechanics as well as quantum-molecular dynamics techniques based on the Roothaan-Hall equations and the Newton motion laws. Different failure mechanisms and mechanical properties are found for CNTs subjected to electric fields and that subjected to tensile load. The electric field induced breaking in CNT begins from the outmost carbon atomic layers while the tensile load breaks the nanotube near its middle at 300 K. Electronic polarization and mechanical deformation induced by an electric field can significantly change the electronic properties of a CNT. Under electric field, the CNT can be stretched but the toughness is much lower than that under mechanical loading. Applied tensile loading causes no electronic polarization even in a metallic tube but it indeed changes the energy gap of the tube, thus exhibits influence on field-emission properties of CNTs. When a tube is tensioned in an electric field, the critical tensile strength of the tube may decrease significantly with increasing intensity of electric field. The coupling of mechanical and electrical behaviours is an important characteristic of CNTs.