Local control of electric current driven shell etching of multiwalled carbon nanotubes

Abstract

We report on a novel method for local control of shell engineering in multiwalled carbon nanotubes (MWNTs) using Joule-heating induced electric breakdown. By modulating the heat dissipation along a nanotube, we can confine its thinning and shell breakdown to occur within localized regions of peak temperatures, which are distributed over one-half of the NT length. The modulation is achieved by using suitably designed nanomachined heat sinks with different degrees of thermal coupling at different parts of a current-carrying nanotube. The location of electric breakdown occurs precisely at the regions of high temperatures predicted by the classical finite-element model of Joule heating in the MWNT. The experiments herein provide new insight into the electric breakdown mechanism and prove unambiguously that shell removal occurs due to thermal stress, underpinning the diffusive nature of MWNTs. The method demonstrated here has the potential to be a powerful tool in realizing MWNT bearings with complex architectures for use in integrated nanoelectromechanical systems (NEMS). In addition, the breakdown current and power in the nanotubes are significantly higher than those observed in nanotubes without heat removal via additional heat sinks. This indicates future avenues for enhancing the performance of MWNTs in electrical interconnect and nanoelectronic applications. Current driven electric breakdown of individual carbon shells [1][2][3][4][5][6][7] is a powerful method for modifying the as-synthesized closed cap nested shell structure of multiwalled carbon nanotubes (MWNTs). In this method, the thermal stress caused by Joule heating of current-carrying nanotubes is used to initiate defects in the nanotube structure and vaporize individual shells with an accompanied reduction in nanotube conductance. The capability of engineering nanotube geometry is expected to find applications in the next-generation of nanoelectromechanical systems. For instance, nanotube linear and rotary bearings [8][9][10][11] Precise control over breakdown location and NT shell architecture is an important requirement for these applications. In previous reports, shell structuring has been performed by connecting the nanotubes to metallic contacts at their distal ends and driving currents [1,2,4,13,15]. With the electrical and phonon transport through MWNTs being diffusive at length scales on the order of a hundred nanometers, Joule-heating induces peak temperatures at nanotube mid-lengths and results in the loss of carbon atoms in the outer shells of these regions between the contacting electrodes. However, with this simple two-electrode configuration, the temperature distribution along the nanotube will always result in shell breakdown at nanotube mid-lengths. Presently, we demonstrate a novel approach to precisely alter, control or restrict the region over which shell structuring occurs. This is achieved by modifying the heat dissipation along the length of a current-carrying nanotube in order to controllably create localized regions ...

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