Cobalt nanoparticle-assisted engineering of multiwall carbon nanotubes

New methods of processing multiwall carbon nanotubes (CNTs) are demonstrated in experiments in the transmission electron microscope (TEM). These include precisely controllable cutting, repairing, and interconnecting of different CNTs with the assistance of an encapsulated Co particle. All processes involve the interactions between the metal and graphitic shells that are driven by combined electrical biasing [using a scanning-tunneling microscope (STM)-TEM setup] of the CNT and focused electron-beam irradiation of a Co-containing region. In particular, we present two CNT soldering processes, that is, Co-joined and Co-catalytic connections. The former process uses a Co particle as the central node to which two CNTs are covalently attached on the opposite sides, and the latter makes use of the segregation of new graphitic shells from the metal at the connecting site, resulting in CNT plumbing. We compare the mechanical robustness of both connection types by direct force measurements in the TEM using an integrated atomic force microscope (AFM) setup. They reveal a tensile strength of 4.2 and 31 GPa, respectively, thus demonstrating the superiority of the Co-catalytic connection whose strength is already comparable to standard CNTs. In addition, all connected nanotubes show metallic conduction. The developed methods could be of particular importance in future nanoelectronic device technology.