Abstract Submitted to the NANOTUBE'02 Workshop:

For various applications in nanotechnology, electronic devices and strong nano-mechanical systems need the establishment of molecular connections among single-walled nanotubes (SWNTs). Coalescence of SWNTs has been observed in-situ under electron irradiation at high temperature in a transmission electron microscope [1]. The merging process is investigated at the atomic level using molecular dynamics simulations. Vacancies induce coalescence via a zipper-like mechanism, imposing a continuous reorganization of atoms on individual tube lattices along adjacent tubes. Other topological defects induce the polymerization of tubes. However, it is also imperative to join and connect nanotubes in a controllable way. Here, we demonstrate for the first time, that electron beam exposure at elevated temperatures, can be used as an effective tool to covalently weld crossed SWNTs in order to create molecular junctions of various geometries. Stable ²X³-, ²Y³-, or ²T³-like junctions have been created in-situ in a transmission electron microscope [2]. Electron beam exposure at high temperatures induces structural defects, which promote the joining of tubes via cross-linking of dangling bonds. The observations of the merging are supported by molecular dynamics simulations, which show that the creation of vacancies and interstitials induces the formation of junctions involving seven- or eight-membered carbon rings at the surface interface between the tubes. Electronic properties of junction models, resembling those observed in the experiments, are also predicted. We envisage that our results will pave the way towards controlled fabrication of nanotube based molecular circuits and network architectures exhibiting exciting electronic and mechanical behaviour.

[1] M. Terrones, H. Terrones, F. Banhart, J.-C. Charlier, and P.M. Ajayan, Science 288, 1226-1229 (2000).
[2] M. Terrones, F. Banhart, N. Grobert, J.-C. Charlier, H. Terrones, and P.M. Ajayan, submitted (2002)