Unmodified nanotube-polymer matrix composites often fail by fiber pull-out. Polyatomic ion beam deposition can induce crosslinking between unfucntionalized carbon nanotubes and polystyrene chains. This strengthens the interaction of the nanotubes with the polymer matrix, creates sp³ and other types of defects in the nanotube walls, and, under the right conditions, toughens the composite.

      In this study, classical molecular dynamic simulations are used to investigate the effect of incident energy and angle orientation on ion beam deposition on a carbon nanotube-polystyrene matrix composites. The ion beam consists of  polyatomic, fluorocarbon ions that are deposited onto single-walled and multi-walled carbon nanotube-polystyrene matrix composite substrates. This study determines the optimum conditions under which ion-beam deposition on these composites enhances their properties. This work is supported by the National Science Foundation under Grant No. CHE-0200838. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

      Due to their unique electrical properties and nanometer-scale sizes, individual carbon nanotubes are considered to be promising candidates for use as nanometer-scale wires, and properly joined single-walled nanotubes could be the building blocks of various electronic devices. For example, a junction formed by two nanotubes, one of which is semiconducting and one of which is metallic, can act as a rectifying diode, while a multiterminal heterojunction, such as a "Y" or "T" junction, works as a transistor. In addition, quantum dot behavior has been observed in two-terminal heterojunctions. Therefore, there has been much research aimed at exploring the production and properties of nanotube junctions. These junctions have been made by several techniques, such as welding with electron beam irradiation, mechanical manipulation with atomic force microscopes, thermal annealing, and chemical functionalization.
      The simulation of electron beam induced welding of crossed carbon nanotubes is considered with classical molecular dynamics simulations. Covalent junctions are predicted to form between various types of carbon nanotubes that contain many defects and are likely to be representative of experimentally welded nanotubes under highly nonequilibrium synthesis conditions. The effect of the junction structure and hydrogen termination of dangling bonds on the mechanical responses of the junctions is also considered. This work is supported by the National Science Foundation under Grant No. CHE-0200838. It is carried out in collaboration with Professor Pawel Keblinski (RPI) and Dr. Fabrizio Cleri (ENEA, Centro Ricerche Casaccia). Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

      Deposition can introduce crosslinks between the concentric shells of a multi-walled carbon nanotubes. This limits the tendency for the inner shell to fail by the "sword-and-sheath" mechanism during deformation. Simulations can determine the mechanisms by which crosslinks and covalent functionalization occur in nanotube-based systems, as well as investigate their effects on the properties of carbon nanotubes. Here, classical molecular dynamics simulations are used to investigate the irradiation of multi-walled carbon nanotubes and bundles of single-walled carbon nanotubes using the reactive empirical bond-order (REBO) potential for hydrocarbons and fluorocarbons to calculate the forces between the atoms. Variables that are investigated include the effects of particle type, incident angle, and ion energies.

      In collaboration with Prof. Hanley and Dr. Rodney Andrews, of the Center for Applied Energy Research at the University of Kentucky, we have examined the deposition of polyatomic ions on carbon nanotube bundles. Classical molecular dynamics simulations consider the deposition of CH₃⁺ on the nanotubes at incident energies of 10, 45 and 80 eV. They predict the chemical functionalization of the nanotubes, the formation of defects on the nanotube walls, and the formation of cross-links between neighboring nanotubes or between the walls of a single nanotube. They also illustrate the manner in which the number of walls in the nanotube and incident energy affect the results. In the experiments multiwalled nanotubes with about 40 shells (average diameter of 25 nm) are synthesized by chemical vapor deposition. CF₃⁺ ions are deposited at incident energies of 10 and 45 eV and then the nanotubes are examined with x-ray photoelectron spectroscopy and scanning electron microscopy. These experiments find strong evidence of chemical functionalization, in agreement with the simulation results. This work was featured on the cover of the December 27, 2001 issue of the Journal of Physical Chemistry B. This work is supported by the National Science Foundation under Grant No. CHE-0200838. Any opinions, findings and conclusions or recomendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).