In situ TEM study on the improvement of contact resistance between a carbon nanotube and metal electrodes by local melting

Abstract

Contact resistance between a multiwalled carbon nanotube (MWNT) and a metal electrode is governed by the contact structure. The relationship between the contact structure and electrical resistance was examined by in situ transmission electron microscopy using a nickel electrode and MWNTs with two kinds of tip structure; close-capped and open-ended. When the current density through the contact region reached a threshold value about 7.6 Â 10 8 A/cm 2 , the MWNT tip was embedded below the nickel surface by local melting of the metal, and the contact resistance was reduced. In the case of the open-ended MWNT, significant reduction of the contact resistance was observed, because inner shells of the MWNT with open cap can connect directly with the electrode.

In situ TEM study on structural and electric conduction properties of a multiwall carbon nanotube connected to a Mo electrode

“…From our previous study related to electric conductive properties of an Au–MWNT–Ni system, R Au + R CNT‐out in Eqs can be estimated to be ca. 5 kΩ.…”

“…They revealed that Joule heating by high current flow brought about fusion of a metal (W) electrode and formation of tungsten carbide, leading to a reduction of contact resistance. Karita et al . also reported structural change of the CNT/metal [gold (Au) and nickel (Ni)] interface and the corresponding reduction of contact resistance during the passage of electric current by in situ TEM.…”

“…However, it is not clear how the structural change induced in joining process of the CNT and metal electrode affect their electric conductive properties. Only a few experiments have been performed to observe the joining process of a CNT and a metal electrode at atomic scale with simultaneous measurement of their current–voltage characteristics . For example, Wang et al .…”

In Situ TEM of Carbon Nanotubes

“…In a microscope operating at 120 kV, two metals were studied, namely, Ni and Au, along with arc-made MWCNTs with two different types of tips, open and closed. Current densities in the order of 10 8 A/cm 2 were reportedly needed to induce melting of the Ni surface at the contact region [ 87 ]. This annealing process led to a marked decrease of the overall electrical resistance, particularly for the open-end nanotubes.…”