Dynamical criteria for Cs ion insertion and adsorption at cap and stem of carbon nanotubes: Ab initio study and comparison with experiment

Unlike lighter alkali metals, cesium is not inserted into carbon nanotubes straightforwardly. To clarify Cs+ insertion and adsorption processes in recent experiments, the Cs⁺ is shot toward the cap and stem of (5,5) and (10,10) armchair nanotubes by performing ab initio molecular dynamics simulations. Considering three relevant factors of collision, i.e., the impact position, impact angle, and the kinetic energy of dopant, we observe that the Cs⁺ with kinetic energy 50 eV is adsorbed on the surface of the nanotube irrespective of the impact angle and impact position. The Cs ⁺ with kinetic energy 100 eV can make a hole on the surface and be encapsulated, or trapped in the middle of the created hole, if the collision route is aiming toward the nanotube stem. If the route is aiming away from the nanotube stern, the Cs⁺ will tear the nanotube's surface and will be scattered off. This makes it possible for other Cs ions to get encapsulated via the torn region. The Cs ions whose energies are 150 eV and aim toward the nanotube stem get encapsulated with minimal deformation of the collision region. The simulation results are supported by Raman scattering spectroscopy experiments and are instructive in doped-nanotube applications such as flat panel displays and nanoelectronic devices.