Test for superconductivity in individual end-bonded MWNTs

Takesue {\it{et al.}} [1] recently reported 12K superconductivity in templated arrays of $\sim 10^4$ ``end-bonded" multi-walled carbon nanotubes (MWNTs). They attributed the occurrence of superconductivity to intershell (interlayer) effects within each MWNT. We have tested this by preparing and measuring {\it{individual}} end-bonded MWNTs, which were grown by arc-discharge without catalyst. High resolution TEM showed they had typical outer (inner) diameters of 10 - 15 nm (1-2 nm), with no visible defects, values verified by AFM and electrical measurements. We also verified by TEM that, as grown, the nanotube ends were closed. We then used a novel nanolithographic approach to facilitate end-bonding ({\it{i.e.}} contacting all layers), which was subsequently verified in $I-V$ tests. Four-probe resistivity was measured for several such individual end-bonded MWNTs, to 1.4 K, including the use of current densities smaller than those used in Ref. 1. No evidence for superconductivity was found. \newline \newline [1] I. Takesue \textit{et al.}, Phys. Rev. Lett. $\bf{96}$, 057001 (2006)